Chemistry Is Everywhere

Everything you hear, see, smell, taste, and touch involves chemistry and chemicals (matter). And hearing, seeing, tasting, and touching all involve intricate series of chemical reactions and interactions in you body. With such an enormous range of topics, it is essential to know about chemistry at some level in order to understand the world around us.

In more formal terms chemistry is the study of matter and the changes it can undergo. Chemists sometimes refer to matter as ‘stuff’, and indeed so it is. Matter is anything that has mass and occupies space. Which is to say, anything you can touch or hold. Common usage might have us believe that ‘chemicals’ are just those substances in laboratories or something that is not a natural substance. Far from it, chemists believe that everything is made of chemicals.

Although there are countless types of matter all around us, this complexity is composed of various combinations of some 100 chemical elements. The names of some of these elements will be familiar to almost everyone. Elements such as hydrogen, chlorine, silver, and copper are part of our everyday knowledge. Far fewer people have heard of selenium or rubidium or hassium.

Nevertheless, all matter is composed of various combinations of these basic elements. The wonder of chemistry is that when these basic particles are combined, they make something new and unique. Consider the element sodium. It is a soft, silvery metal. It reacts violently with water, giving off hydrogen gas and enough heat to make the hydrogen explode. Nasty ‘stuff’. Also consider chlorine, a green gas when at room temperature. It is very caustic and choking, and is nasty enough that it was used as a horrible chemical gas weapon in the last century. So what kind of horrible mess is produced when sodium and chlorine are combined? Nothing more than sodium chloride, common table salt. Table salt does not explode in water or choke us; rather, it is a common additive for foods we eat everyday.

And so it is with chemistry, understanding the basic properties of matter and learning how to predict and explain how they change when they react to form new substances is what chemistry and chemists are all about.

Chemistry is not limited to beakers and laboratories. It is all around us, and the better we know chemistry, the better we know our world.

Sumber: American Chemical Society

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Biochemistry

Biochemistry is the study of the molecular basis of cellular function. It has evolved into the common language for translating the advances of molecular biology into cellular and chemical terms. In the Department of Biochemistry and Molecular Biology, we study a broad range of cellular activities, from gene transcription to the structure and function of proteins, DNA, RNA, and lipid membranes. Like all biologists, we attempt to correlate structure with function, but at a molecular level of detail, defining not only the structures that govern function, but also the chemical reactions involved.

The field of biochemistry brings together the areas of molecular genetics, cell biology, and each of these headings can be further subdivided into the classical areas of enzymology; structure and function of nucleic acid proteins, carbohydrates, and lipids; metabolism; and biogenetics.

Our faculty provides students and postdoctoral fellows with a research experience aimed at understanding fundamental mechanisms and the structural basis of cellular processes. The advances of the next decade will rely on a blend of structural biology, molecular biology, and molecular genetics. We integrate these fields on topics that span from regulation of gene expression and chromatin structure, to cell signaling, cell cycle control, RNA, and protein structure and function, and receptor-ligand or enzyme-substrate interactions. We utilize prokaryotic, nematode, and mammalian model systems and incorporate advanced genomics and proteomics approaches and instrumentation. We encourage you to contact us and visit out website and state of the art facilities, and learn more about research programs and graduate education.

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Organic Chemistry

Organic chemistry is a discipline within chemistry which involves the scientific study of the structure, properties, composition, reactions, and preparation (by synthesis or by other means) of chemical compounds consisting primarily of carbon and hydrogen, which may contain any number of other elements, including nitrogen, oxygen, the halogens as well as phosphorus, silicon and sulfur.

The original definition of "organic" chemistry came from the misconception that organic compounds were always related to life processes. However, organic molecules can be produced by processes not involving life. Life as we know it also depends on inorganic chemistry. For example, many enzymes rely on transition metals such as iron and copper; and materials such as shells, teeth and bones are part organic, part inorganic in composition. Apart from elemental carbon, only certain classes of carbon compounds (such as oxides, carbonates, and carbides) are conventionally considered inorganic. Biochemistry deals mainly with the natural chemistry of biomolecules such as proteins, nucleic acids, and sugars.

Because of their unique properties, multi-carbon compounds exhibit extremely large variety and the range of application of organic compounds is enormous. They form the basis of, or are important constituents of many products (paints, plastics, food, explosives, drugs, petrochemicals, to name but a few) and (apart from a very few exceptions) they form the basis of all earthly life processes.

The different shapes and chemical reactivities of organic molecules provide an astonishing variety of functions, like those of enzyme catalysts in biochemical reactions of live systems.

Current (as of 2008) trends in organic chemistry include chiral synthesis, green chemistry, microwave chemistry, fullerenes and microwave spectroscopy.Historical highlights
Friedrich Wöhler
Friedrich Wöhler

At the beginning of the nineteenth century chemists generally thought that compounds from living organisms were too complicated in structure to be capable of artificial synthesis from non-living things, and that a 'vital force' or vitalism conferred the characteristics of living beings on this form of matter. They named these compounds 'organic', and preferred to direct their investigations toward inorganic materials that seemed more promising.

Organic chemistry received a boost when it was realized that these compounds could be treated in ways similar to inorganic compounds and could be created in the laboratory by means other than 'vital force'. Around 1816 Michel Chevreul started a study of soaps made from various fats and alkali. He separated the different acids that, in combination with the alkali, produced the soap. Since these were all individual compounds, he demonstrated that it was possible to make a chemical change in various fats (which traditionally come from organic sources), producing new compounds, without 'vital force'. In 1828 Friedrich Wöhler first manufactured the organic chemical urea (carbamide), a constituent of urine, from the inorganic ammonium cyanate NH4OCN, in what is now called the Wöhler synthesis. Although Wöhler was, at this time as well as afterwards, cautious about claiming that he had thereby destroyed the theory of vital force, most have looked to this event as the turning point.

A great next step was when in 1856 William Henry Perkin, while trying to manufacture quinine, again accidentally came to manufacture the organic dye now called Perkin's mauve, which by generating a huge amount of money greatly increased interest in organic chemistry. Another step was the laboratory preparation of DDT by Othmer Zeidler in 1874, but the insecticide properties of this compound were not discovered until much later.

The crucial breakthrough for the theory of organic chemistry was the concept of chemical structure, developed independently and simultaneously by Friedrich August Kekule and Archibald Scott Couper in 1858. Both men suggested that tetravalent carbon atoms could link to each other to form a carbon lattice, and that the detailed patterns of atomic bonding could be discerned by skillful interpretations of appropriate chemical reactions.

The history of organic chemistry continues with the discovery of petroleum and its separation into fractions according to boiling ranges. The conversion of different compound types or individual compounds by various chemical processes created the petroleum chemistry leading to the birth of the petrochemical industry, which successfully manufactured artificial rubbers, the various organic adhesives, the property-modifying petroleum additives, and plastics.

The pharmaceutical industry began in the last decade of the 19th century when acetylsalicylic acid (more commonly referred to as aspirin) manufacture was started in Germany by Bayer. The first time a drug was systematically improved was with arsphenamine (Salvarsan). Numerous derivatives of the dangerously toxic atoxyl were systematically synthesized and tested by Paul Ehrlich and his group, and the compound with best effectiveness and toxicity characteristics was selected for production.

Early examples of organic reactions and applications were serendipitous, such as Perkin's accidental discovery of Perkin's mauve. However, from the 20th century, the progress of organic chemistry allowed for synthesis of specifically selected compounds or even molecules designed with specific properties, as in drug design. The process of finding new synthesis routes for a given compound is called total synthesis. Total synthesis of complex natural compounds started with urea, increased in complexity to glucose and terpineol, and in 1907, total synthesis was commercialized the first time by Gustaf Komppa with camphor. Pharmaceutical benefits have been substantial, for example cholesterol-related compounds have opened ways to synthesis of complex human hormones and their modified derivatives. Since the start of the 20th century, complexity of total syntheses has been increasing, with examples such as lysergic acid and vitamin B12. Today's targets feature tens of stereogenic centers that must be synthesized correctly with asymmetric synthesis.

Biochemistry, the chemistry of living organisms, their structure and interactions in vitro and inside living systems, has only started in the 20th century, opening up a brand new chapter of organic chemistry with enormous scope.

[edit] Classification of organic substances

[edit] Description and nomenclature

Classification is not possible without having a full description of the individual compounds. In contrast with inorganic chemistry, in which describing a chemical compound can be achieved by simply enumerating the chemical symbols of the elements present in the compound together with the number of these elements in the molecule, in organic chemistry the relative arrangement of the atoms within a molecule must be added for a full description.

One way of describing the molecule is by drawing its structural formula. Because of molecular complexity, simplified systems of chemical notation have been developed. The latest version is the line-angle formula, which achieves simplicity without introducing ambiguity. In this system, the endpoints and intersections of each line represent one carbon, and hydrogens can either be notated or assumed to be present by implication. Some disadvantages of chemical notation are that they are not easily described by words and they are not easily printable. These problems have been addressed by describing molecular structures using organic nomenclature .

Because of the difficulties arising from the very large number and variety of organic compounds, chemists realized early on that the establishment of an internationally accepted system of naming organic compounds was of paramount importance. The Geneva Nomenclature was born in 1892 as a result of a number of international meetings on the subject.

It was also realized that as the family of organic compounds grew, the system would have to be expanded and modified. This task was ultimately taken on by the International Union on Pure and Applied Chemistry (IUPAC). Recognizing the fact that in the branch of biochemistry the complexity of organic structures increases, the IUPAC organization joined forces with the International Union of Biochemistry and Molecular Biology, IUBMB, to produce a list of joint recommendations on nomenclature.

Later, as the numbers and complexities of organic molecules grew, new recommendations were made within IUPAC for simplification. The first such recommendation was presented in 1951 when a cyclic benzene structure was named a cyclophane. Later recommendations extended the method to the simplification of other complex cyclic structures, including heterocyclics, and named such structures phanes.

For ordinary communication, to spare a tedious description, the official IUPAC naming recommendations are not always followed in practice except when it is necessary to give a concise definition to a compound, or when the IUPAC name is simpler (viz. ethanol versus ethyl alcohol). Otherwise the common or trivial name may be used, often derived from the source of the compound.

In summary, organic substances are classified by their molecular structural arrangement and by what other atoms are present along with the chief (carbon) constituent in their makeup, whilst in a structural formula, hydrogen is implicitly assumed to occupy all free valences of an appropriate carbon atom which remain after accounting for branching, other element(s) and/or multiple bonding.

[edit] Hydrocarbons and functional groups

Main articles: Hydrocarbon and Functional group

The family of carboxylic acids contains a carboxyl (-COOH) functional group. Acetic acid is an example.
The family of carboxylic acids contains a carboxyl (-COOH) functional group. Acetic acid is an example.

Classification normally starts with the hydrocarbons: compounds which contain only carbon and hydrogen. For sub-classes see below. Other elements present themselves in atomic configurations called functional groups which have decisive influence on the chemical and physical characteristics of the compound; thus those containing the same atomic formations have similar characteristics, which may be: miscibility with water, acidity/alkalinity, chemical reactivity, oxidation resistance, and others. Some functional groups are also radicals, similar to those in inorganic chemistry, defined as polar atomic configurations which pass during chemical reactions from one chemical compound into another without change.

Some of the elements of the functional groups (O, S, N, halogens) may stand alone and the group name is not strictly appropriate, but because of their decisive effect on the way they modify the characteristics of the hydrocarbons in which they are present they are classed with the functional groups, and their specific effect on the properties lends excellent means for characterisation and classification.

Referring to the hydrocarbon types below, many, if not all of the functional groups which are typically present within aliphatic compounds are also represented within the aromatic and alicyclic group of compounds, unless they are dehydrated, which would lead to non-reacting co-optional groups.

Reference is made here again to the organic nomenclature, which shows an extensive (if not comprehensive) number of classes of compounds according to the presence of various functional groups, based on the IUPAC recommendations, but also some based on trivial names. Putting compounds in sub-classes becomes more difficult when more than one functional group is present.

Two overarching chain type categories exist: Open Chain aliphatic compounds and Closed Chain cyclic compounds. Those in which both open chain and cyclic parts are present are normally classed with the latter.

[edit] Aliphatic compounds

Main article: Aliphatic compound

The aliphatic hydrocarbons are subdivided into three groups, homologous series according to their state of saturation: paraffins alkanes without any double or triple bonds, olefins alkenes with double bonds, which can be mono-olefins with a single double bond, di-olefins, or di-enes with two, or poly-olefins with more. The third group with a triple bond is named after the name of the shortest member of the homologue series as the acetylenes alkynes. The rest of the group is classed according to the functional groups present.

From another aspect aliphatics can be straight chain or branched chain compounds, and the degree of branching also affects characteristics, like octane number or cetane number in petroleum chemistry.

[edit] Aromatic and alicyclic compounds
Benzene is one of the best-known aromatic compounds as it is one of the simplest aromatics.
Benzene is one of the best-known aromatic compounds as it is one of the simplest aromatics.

Cyclic compounds can, again, be saturated or unsaturated. Because of the bonding angle of carbon, the most stable configurations contain six carbon atoms, but while rings with five carbon atoms are also frequent, others are rarer. The cyclic hydrocarbons divide into alicyclics and aromatics (also called arenes).

Of the alicyclic compounds the cycloalkanes do not contain multiple bonds, whilst the cycloalkenes and the cycloalkynes do. Typically this latter type only exists in the form of large rings, called macrocycles. The simplest member of the cycloalkane family is the three-membered cyclopropane.


Aromatic hydrocarbons contain conjugated double bonds. One of the simplest examples of these is benzene, the structure of which was formulated by Kekulé who first proposed the delocalization or resonance principle for explaining its structure. For "conventional" cyclic compounds, aromaticity is conferred by the presence of 4n + 2 delocalized pi electrons, where n is an integer. Particular instability (antiaromaticity) is conferred by the presence of 4n conjugated pi electrons.

The characteristics of the cyclic hydrocarbons are again altered if heteroatoms are present, which can exist as either substituents attached externally to the ring (exocyclic) or as a member of the ring itself (endocyclic). In the case of the latter, the ring is termed a heterocycle. Pyridine and furan are examples of aromatic heterocycles while piperidine and tetrahydrofuran are the corresponding alicyclic heterocycles. The heteroatom of heterocyclic molecules is generally oxygen, sulfur, or nitrogen, with the latter being particularly common in biochemical systems.

Rings can fuse with other rings on an edge to give polycyclic compounds. The purine nucleoside bases are notable polycyclic aromatic heterocycles. Rings can also fuse on a "corner" such that one atom (almost always carbon) has two bonds going to one ring and two to another. Such compounds are termed spiro and are important in a number of natural products.

[edit] Polymers

Main article: Polymer

This swimming board is made of polystyrene, an example of a polymer
This swimming board is made of polystyrene, an example of a polymer

One important property of carbon in organic chemistry is that it can form certain compounds, the individual molecules of which are capable of attaching themselves to one another, thereby forming a chain or a network. The process is called polymerization and the chains or networks polymers, while the source compound is a monomer. Two main groups of polymers exist: those artificially manufactured are referred to as industrial polymers [4] or synthetic polymers and those naturally occurring as biopolymers.

Since the invention of the first artificial polymer, bakelite, the family has quickly grown with the invention of others. Common synthetic organic polymers are polyethylene or polythene, polypropylene, nylon, teflon or PTFE, polystyrene, polyesters, polymethylmethacrylate (commonly known as perspex or plexiglas) polyvinylchloride or PVC, and polyisobutylene an important artificial or synthetic rubber also the polymerised butadiene, a rubber component.

The examples are generic terms, and many varieties of each of these may exist, with their physical characteristics fine tuned for a specific use. Changing the conditions of polymerisation changes the chemical composition of the product by altering chain length, or branching, or the tacticity. With a single monomer as a start the product is a homopolymer. Further, secondary component(s) may be added to create a heteropolymer (co-polymer) and the degree of clustering of the different components can also be controlled. Physical characteristics, such as hardness, density, mechanical or tensile strength, abrasion resistance, heat resistance, transparency, colour, etc. will depend on the final composition.

[edit] Biomolecules
Maitotoxin, a complex organic biological toxin.
Maitotoxin, a complex organic biological toxin.

Biomolecular chemistry is a major category within organic chemistry which is frequently studied by biochemists. Many complex multi-functional group molecules are important in living organisms. Some are long-chain biopolymers, and these include proteins, DNA, RNA and the polysaccharides such as starches in animals and celluloses in plants. The other main classes are amino acids (monomer building blocks of proteins), carbohydrates (which includes the polysaccharides), the nucleic acids (which include DNA and RNA as polymers), and the lipids. In addition, animal biochemistry contains many small molecule intermediates which assist in energy production through the Krebs cycle, and produces isoprene, the most common hydrocarbon in animals. Isoprenes in animals form the important steroid structural (cholesterol) and steroid hormone compounds; and in plants form terpenes, terpenoids, some alkaloids, and a unique set of structural hydrocarbons called biopolymer polyisoprenoids present in latex sap which is the basis for making rubber.

[edit] Buckyballs

Buckminsterfullerenes, also known as Buckyballs, are amongst the most fascinating molecules engineered by organic chemists to date. Their spherical structure manifests many electronic properties and new research in the synonymous carbon nanotubes is fascinating.

Fullerenes are rather oddly classed with organic chemistry as they do not fit the definition. However, it seems, that the classification is justified by the fact that they are a diversion for organic chemists.

[edit] Others

Organic compounds containing bonds of carbon to nitrogen, oxygen and the halogens are not normally grouped separately. Others are sometimes put into major groups within organic chemistry and discussed under titles such as organosulfur chemistry, organometallic chemistry, organophosphorus chemistry and organosilicon chemistry.

[edit] Characteristics of organic substances
The structure of methane by pictorial representation of a Lewis diagram showing the sharing of electronpairs between atomic nuclei in a covalent bond. Please do not form the impression from the diagram that the real picture is two-dimensional, because this is not the case.
The structure of methane by pictorial representation of a Lewis diagram showing the sharing of electronpairs between atomic nuclei in a covalent bond. Please do not form the impression from the diagram that the real picture is two-dimensional, because this is not the case.

Organic compounds are generally covalently bonded. This allows for unique structures such as long carbon chains and rings. The reason carbon is excellent at forming unique structures and that there are so many carbon compounds is that carbon atoms form very stable covalent bonds with one another (catenation). In contrast to inorganic materials, organic compounds typically melt, boil, sublimate, or decompose below 300 °C. Neutral organic compounds tend to be less soluble in water compared to many inorganic salts, with the exception of certain compounds such as ionic organic compounds and low molecular weight alcohols and carboxylic acids where hydrogen bonding occurs.

Organic compounds tend to dissolve in organic solvents which are either pure substances like ether or ethyl alcohol, or mixtures, such as the paraffinic solvents such as the various petroleum ethers and white spirits, or the range of pure or mixed aromatic solvents obtained from petroleum or tar fractions by physical separation or by chemical conversion. Solubility in the different solvents depends upon the solvent type and on the functional groups if present. Solutions are studied by the science of physical chemistry. Like inorganic salts, organic compounds may also form crystals. A unique property of carbon in organic compounds is that its valency does not always have to be taken up by atoms of other elements, and when it is not, a condition termed unsaturation results. In such cases we talk about carbon carbon double bonds or triple bonds. Double bonds alternating with single in a chain are called conjugated double bonds. An aromatic structure is a special case in which the conjugated chain is a closed ring.

[edit] Molecular structure elucidation
Molecular models of caffeine
Molecular models of caffeine

Organic compounds consist of carbon atoms, hydrogen atoms, and functional groups. The valence of carbon is 4, and hydrogen is 1, functional groups are generally 1. From the number of carbon atoms and hydrogen atoms in a molecule the degree of unsaturation can be obtained. Many, but not all structures can be envisioned by the simple valence rule that there will be one bond for each valence number. The knowledge of the chemical formula for an organic compound is not sufficient information because many isomers can exist. Organic compounds often exist as mixtures. Because many organic compounds have relatively low boiling points and/or dissolve easily in organic solvents there exist many methods for separating mixtures into pure constituents that are specific to organic chemistry such as distillation, crystallization and chromatography techniques. There exist several methods for deducing the structure an organic compound. In general usage are (in alphabetical order):

* Crystallography: This is the most precise method for determining molecular geometry; however, it is very difficult to grow crystals of sufficient size and high quality to get a clear picture, so it remains a secondary form of analysis. Crystallography has seen especially extensive use in biochemistry (for protein structure determination) and in the characterization of organometallic catalysts, which often possess significant molecular symmetry.
* Elemental analysis: A destructive method used to determine the elemental composition of a molecule. See also mass spectrometry, below.
* Infrared spectroscopy: Chiefly used to determine the presence (or absence) of certain functional groups.
* Mass spectrometry: Used to determine the molecular weight of a compound and from mass spectrum analysis its structure. High resolution mass spectrometry can often identify the precise formula of a compound through knowledge of isotopic masses and abundances; it is thus sometimes used in lieu of elemental analysis.
* Nuclear magnetic resonance (NMR) spectroscopy identifies different nuclei based on their chemical environment. This is the most important and commonly used spectroscopic technique for organic chemists, often permitting complete assignment of atom connectivity and even stereochemistry given the proper set of spectroscopy experiments (e.g. correlation spectroscopy).
* Optical rotation: Distinguishes between two enantiomers of a chiral compound based on the sign of rotation of plane polarized light. If the specific rotation of an enantiomer is known, the magnitude of rotation also gives the ratio of enantiomers in a mixed sample, though HPLC with a chiral column also can supply this information.
* UV/VIS spectroscopy: Used to determine degree of conjugation in the system. While still sometimes used to characterize molecules, UV/VIS is more commonly used to quantitate how much of a known compound is present in a (typically liquid) sample.

Additional methods are provided by analytical chemistry.

[edit] Organic reactions

Organic reactions are chemical reactions involving organic compounds. While pure hydrocarbons undergo certain limited classes of reactions, many more reactions which organic compounds undergo are largely determined by functional groups. The general theory of these reactions involves careful analysis of such properties as the electron affinity of key atoms, bond strengths and steric hindrance. These issues can determine the relative stability of short-lived reactive intermediates, which usually directly determine the path of the reaction. An example of a common reaction is a substitution reaction written as:

Nu− + C-X → C-Nu + X−

where X is some functional group and Nu is a nucleophile.

There are many important aspects of a specific reaction. Whether it will occur spontaneously or not is determined by the Gibbs free energy change of the reaction. The heat that is either produced or needed by the reaction is found from the total enthalpy change. Other concerns include whether side reactions occur from the same reaction conditions. Any side reactions which occur typically produce undesired compounds which may be anywhere from very easy or very difficult to separate from the desired compound.

[edit] Synthetic organic chemistry

Main article: Organic synthesis

A synthesis designed by E.J. Corey for oseltamivir (Tamiflu).
A synthesis designed by E.J. Corey for oseltamivir (Tamiflu).

Synthetic organic chemistry is an applied science as it borders engineering, the "design, analysis, and/or construction of works for practical purposes". Organic synthesis of a novel compound is a problem solving task, where a synthesis is designed for a target molecule by selecting optimal reactions from optimal starting materials. Complex compounds can have tens of reaction steps that sequentially build the desired molecule. The synthesis proceeds by utilizing the reactivity of the functional groups in the molecule. For example, a carbonyl compound can be used as a nucleophile by converting it into an enolate, or as an electrophile; the combination of the two is called the aldol reaction. Designing practically useful syntheses always requires conducting the actual synthesis in the laboratory. The scientific practice of creating novel synthetic routes for complex molecules is called total synthesis.

There are several strategies to design a synthesis. The modern method of retrosynthesis, developed by E.J. Corey, starts with the target molecule and splices it to pieces according to known reactions. The pieces, or the proposed precursors, receive the same treatment, until available and ideally inexpensive starting materials are reached. Then, the retrosynthesis is written in the opposite direction to give the synthesis. A "synthetic tree" can be constructed, because each compound and also each precursor has multiple syntheses.(http://en.wikipedia.org/)

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The Chemical Elements

INTRODUCTION

What do we mean by a chemical element? A chemical element is matter, all of whose atoms are alike in having the same positive charge on the nucleus and the same number of extra-nuclear electrons. As we shall see in the following elemental review, the origin of the chemical elements show a wide diversity with some of these elements having an origin in antiquity, other elements having been discovered within the past few hundred years and still others have been synthesized within the past fifty years via nuclear reactions on heavy elements since these other elements are unstable and radioactive and do not exist in nature.

The names of the various chemical elements come from many sources including mythological concepts or characters; places, areas or countries; properties of the element or its compounds, such as color, smell or its inability to combine; and the names of scientists. There are also some miscellaneous names as well as some obscure names for particular elements.

The basis for the claim of discovery of an element has varied over the centuries. The method of discovery of the chemical elements in the late eighteenth and the early nineteenth centuries used the properties of the new substances, their separability, the colors of their compounds, the shapes of their crystals and their reactivity to determine the existence of new elements. In those early days, atomic weight values were not available, and there was no spectral analysis that would later be supplied by arc, spark, absorption, phosphorescent or x-ray spectra. Also in those days, there were many claims, e.g., the discovery of certain rare earth elements of the lanthanide series, which involved the discovery of a mineral ore, from which an element was later extracted. The honor of discovery has often been accorded not to the person who first isolated the element but to the person who discovered the original mineral itself, even when the ore was impure and that ore actually contained many elements. The reason for this is that in the case of these rare earth elements, the "earth" now refers to oxides of a metal not to the metal itself. This fact was not realized at the time of their discovery, until the English chemist Humphry Davy showed that earths were compounds of oxygen and metals in 1808.

Although the atomic weight of an element and spectral analysis of that element were not available in the early days, both of these elemental properties would be required before discovery of the element would be accepted by the latter part of the nineteenth century. In general, the requirements for discovery claims have tightened through the years and claims that were previously accepted would no longer meet the minimum constraints now imposed. There are also cases where the honor of discovery is not given to the first person who actually discovered the element but to the first person to claim the discovery in print. If a publication was delayed, the discoverer has often historically been "scooped" by another scientist.

This leads to the question of who should be considered the ultimate discoverer of a chemical element? Should it be the first person to describe the initial properties, the one who found the oxide or the metal, the one who separated the element or the first one to publish their results? On the matter of publication, the Swedish chemist Jons Jacob Berzelius published an annual review (equivalent to our present abstract service) during the early nineteenth century. Berzelius usually cited articles published in other journals, but he also reported on the work in his laboratory which had not yet been published. This enabled his assistant Carl-Gustav Mosander to receive early credit for work that Mosander chose not to formally publish until many years later after he had worked out all of the details. In the element review, we shall see that the answer to the above questions would be any of the above criteria could qualify for discovery of particular elements.

DETERMINING THE NAMES OF THE CHEMICAL ELEMENTS

Names of the chemical elements are determined by the acceptance of the chemical community, the priority rights of the discoverer not withstanding. We shall see long-standing disputes among a number of elements. For some of these elements, this involved both national pride and rivalry between French and German scientists for some of the older elements and Russian and American scientists in more recent times.

At the beginning of the twentieth century, the International Committee on Atomic Weights (ICAW) was formed. Although the ICAW did not set internationally approved names, a name with an atomic weight value in their table lent support for the adoption of that name by the chemical community. Twenty years later, the ICAW became a part of the International Union of Pure and Applied Chemistry (IUPAC) when it was formed. IUPAC was called the International Union of Chemistry in early days between 1930 and 1950. When the IUPAC Commission on Atoms officially disbanded in 1949, the responsibility for acceptance of the name of a chemical element was given by IUPAC to its Commission on Nomenclature of Inorganic Chemistry (CNIC).

The CNIC does not deny the right of a discoverer to propose a name for a new chemical element. However, the approved names of the elements should differ as little as possible in different languages; the names should be based on practicality and prevailing usage and finally the choice of the name carries no implication at all about the priority of discovery. A number of examples of this last point will be seen in the element review.

SPECIAL DIFFICULTIES WITH THE RARE EARTH ELEMENTS

The discovery of the rare earth elements provide a long history of almost two hundred years of trial and error in the claims of element discovery starting before the time of Dalton's theory of the atom and determination of atomic weight values, Mendeleev's periodic table, the advent of optical spectroscopy, Bohr's theory of the electronic structure of atoms and Moseley's x-ray detection method for atomic number determination. The fact that the similarity in the chemical properties of the rare earth elements make them especially difficult to chemically isolate led to a situation where many mixtures of elements were being mistaken for elemental species. As a result, atomic weight values were not nearly as useful because the lack of separation meant that additional elements would still be present within an oxide and lead to inaccurate atomic weight values. Very pure rare earth samples did not become a reality until the mid twentieth century.

Prior to the proposal of the Periodic Table, there was no information available on how many chemical elements could possibly exist. Even after the appearance of the numerous periodic tables of chemical elements, the rare earth elements were an especially difficult case because they could not be properly arranged into any of the Tables. Until the twentieth century, fractional crystallization was the only method of purification of elements. In most cases, this required thousands of recrystallizations involving months of work. As a result, there is a long list of various false claims among the rare earth elements, some of which are detailed below.

The erroneous element names include: junonium, thorine, vestium, sirium, didymium, donarium, wasmium, mosandium, philippium, decipium, ytterbium, columbium, rogerium, austrium, russium, mssrium, demonium, metacerium, damarium, lucium, kosmium, neokosmium, glaucodymium, monium, victorium, euxenium, carolinium, berzelium, incognitium, ionium, celtium, denebium, dubhium, eurosamarium, welsium, nipponium and moseleyum.

Of course, mistaken elements are not restricted to the rare earth elements only. Other elemental errors produced such names as polinium, ilmenium, neptunium, pelopium and davyum.

It should be noted that the ytterbium listed above was a mixture discovered in the mineral erbia by de Marignac in 1878 and not the neoytterbium/aldebaranium element renamed ytterbium that was found in the mineral ytterbia. The columbium was a mixture found in the mineral samarskite and was not the present day columbium/niobium. The ionium listed above was a mixture of terbium and gadolinium that was found in the mineral yttria and does not refer to 230Th. Finally, the neptunium refers to material found in niobium/tantalum minerals and does not refer to the 1940 discovery of the trans-uranium element produced via a neutron capture reaction on a uranium sample.

CONTROVERSIAL HEAVY ELEMENTS

During the last half of the twentieth century, there were many opposing claims, which have taken on a nationalistic rivalry and a fight over when and where an element was "actually discovered" and who has the right to name that element. As mentioned above, IUPAC has taken the position that the name IUPAC proposes for an element carries no implication regarding the priority of the discovery but is merely related to the general usage of a name in the literature. Elements exist where the accepted name was proposed on the basis of an erroneous discovery of that element but widespread usage has dictated the continued use of the original name, even after the error has been discovered (see nobelium in the element list). Historically, new elements have been proposed and accepted in the past on the basis of evidence that would not meet the criteria of today.

Controversy about the first synthesis of new chemical elements in the trans-lawrencium region has recently been resolved by a joint IUPAC and IUPAP (International Union of Pure and Applied Physics) committee. CNIC has assigned names that appear to have been internationally accepted for these elements. Although I have relied on the IUPAC/IUPAP document to discuss elements up to Meitnerium, for elements above Z = 109, the analysis provided is strictly my own due to my reading and interpretation of the scientific literature.

INDIVIDUAL ELEMENT NAMES AND HISTORY

The following list is given alphabetically by element name and provides the origin of the names of the elements and information on their discoverers and/or isolaters.

Actinium - the atomic number is 89 and the chemical symbol is Ac. The name derives from the Greek, aktis or akinis for "beam or ray" because in equilibrium with its decay products, actinium is a powerful source of alpha radiation. The discovery has been credited to the French chemist Andre-Louis Debierne in 1899. It was independently discovered by German chemist Friedrich Oskar Giesel in 1902, who called it emanium. It is thought that Debierne's original preparation actually consisted of two thorium isotopes, 227Th and 230Th, but there was confusion in those early discoveries in radioactivity and Debierne's claim prevailed and his name of actinium has been retained to this day. The longest half-life associated with this unstable element is 21.77 year 227Ac.

Aluminium - the atomic number is 13 and the chemical symbol is Al. Although the name was originally called alumium, it was later changed to aluminum. Internationally, the element is referred to as aluminium, to conform with the "ium" ending of most metallic elements. The name derives from the Latin, alum and alumen for "stringent", since the early Romans called any substance with a stringent taste alum. The element was known in prehistoric times. In 1825, the Danish physicist, Hans Christian Oersted, isolated impure aluminium. The pure metal was first isolated by the German chemist Friedrich Wohler in 1827.

Americium - the atomic number is 95 and the chemical symbol is Am. The name derives from "America" where it was first synthesized in a series of successive neutron capture reactions in the element plutonium, 239Pu, in a nuclear reactor in 1944 by American scientists under Glenn T. Seaborg at the University of California lab in Berkeley, California, using the nuclear reaction 239Pu (n,γ) 240Pu (n,γ) 241Pu -> β- -> 241Am. Americium is the sixth element in the Actinide series of elements and is named in analogy to Europium, which is the sixth element in the Lanthanide series of elements. The longest half-life associated with this unstable element is 7370 year 243Am.

Antimony - the atomic number is 51 and the chemical symbol is Sb. The name derives from the Greek, anti + monos for "not alone or not one" because it was found in many compounds. The chemical symbol, Sb, comes from the original name, stibium, which is derived from the Greek stibi for "mark", since it was used for blackening eyebrows and eyelashes. The name was changed from stibium to antimonium to antimony. The minerals stibnite (Sb2S3) and stibine (SbH3) are two of more than one hundred mineral species, which were known in the ancient world.

Argon - the atomic number is 18 and the chemical symbol was originally just "A" but this symbol was changed to "Ar" in 1957. The name is derived from the Greek argos for "lazy or inactive" because it did not combine with other elements. It was discovered in 1895 by the Scottish chemist William Ramsay and the English physicist Robert John Strutt (Lord Rayleigh) in liquified atmospheric air. Rayleigh's initial interest was generated when he followed up on a problem posed by the English physicist Henry Cavendish in 1785, i.e., when oxygen and nitrogen were removed from air, there was an unknown residual gas remaining.

Arsenic, - the atomic number is 33 and the chemical symbol is As. The name derives from the Latin arsenicum and the Greek arsenikos for the arsenic ore "yellow orpiment" (As2S3, an ancient dye stuff) and sounds similar to the Greek arsenikon for "male or potent", perhaps referring to its poisonous properties. The term orpiment is perhaps a corruption of auripigmentum meaning gold color. Arsenic was also known in prehistoric times for its poisonous sulfides. German scientist and philosopher, Albert von Bollstadt (Albert the Great/Albertus Magnus) is thought to have obtained the metal around 1250 but this is uncertain.

Astatine - the atomic number is 85 and the chemical symbol is At. The name derives from the Greek astatos for "unstable" since it is an unstable element. It was first thought to have been discovered in nature in 1931 and was named alabamine. When it was determined that there are no stable nuclides of this element in nature, that claim was discarded. It was later shown that astatine had been synthesized by the physicists Dale R. Corson, Kenneth R. Mackenzie and Emilio Segre at the University of California lab in Berkeley, California in 1940 who bombarded bismuth with alpha particles, in the reaction 209Bi( 4He, 2n) 211At. Independently, a claim about finding some x-ray lines of astatine was the basis for claiming discovery of an element helvetium, which was made in Bern, Switzerland. However, the very short half-life precluded any chemical separation and identification. The longest half-life associated with this unstable element is 8.1 hour 210At.

Barium - the atomic number is 56 and the chemical symbol is Ba. The name is derived from the Greek barys for "heavy" since it was found in the mineral heavy spar (BaSO4). It was discovered by the Swedish pharmacist and chemist Carl Wilhelm Scheele in 1774 and it was first isolated by the British chemist Humphry Davy in 1808.

Berkelium - the atomic number is 97 and the chemical symbol is Bk. The name is derived fromBerkeley, the town in California where the element was first synthesized in 1949 by the American scientific team under the American chemist Glenn T. Seaborg, using the nuclearreaction 241Am( 4He, 2n) 243Bk. It is the eighth element in the Actinide series of the elements and was named in analogy with Terbium (for Ytterby the town in Sweden whose mine produced the ore), which is the eighth element in the Lanthanide series of the elements. The longest half-life associated with this unstable element is 1400 year 247Bk.

Beryllium - the atomic number is 4 and the chemical symbol is Be. The name derives from the Greek word berryllos for "Beryl" (3BeO.Al203.6Si02) the gem-stone in which it is found. It was discovered by the French chemist and pharmacist Nicholas-Louis Vauquelin in beryl and emerald in 1797. The element was first separated in 1828 by the French chemist Antoine-Alexandre­Brutus Bussy and independently by the German chemist Friedrich Wohler. Since the salts of beryllium have a sweet taste, the element was also known for many years by the symbol GI and the name glucinium from the Greek glykys for "sweet", until IUPAC's CNIC selected the name beryllium in 1949 based on consideration of prevailing usage.

Bismuth - the atomic number is 83 and the chemical symbol is Bi. The name derives from the German weisse masse for "white mass" (the name later altered to wismuth and bisemutum) from the color of its oxides. The ancients did not distinquish bismuth from lead. The French chemist Claude-Francois Geoffroy (the younger) showed that bismuth was distinct from lead in 1753.

Bohrium - the atomic number is 107 and the chemical symbol is Bh. The name derives from the Danish physicist Niels Bohr, who developed the theory of the electronic structure of the atom. The first synthesis of this element is credited to the laboratory of the GSI (Center for Heavy-Ion Research) under the leadership of the German scientists Peter Armbruster and Gunther Miinzenberg at Darmstadt, Germany in 1981, using the reaction 209Bi( 54Cr, n) 262Bh. The longest half-life associated with this unstable element is 17 second 267Bh.

Boron - the atomic number is 5 and the chemical symbol is B. The name derives from the Arabic buraq for "white". Although its compounds were known for thousands of years, it was not isolated until 1808 when the French chemists Louis-Joseph Gay-Lussac and Louis-Jacques Thenard obtained boron in an impure state and the English chemist, Humphry Davy, prepared pure boron by electrolysis.

Bromine - the atomic number is 35 and the chemical symbol is Br. The name derives from the Greek bromos for "stench or bad odor". It was first prepared by the German chemist Carl Lowig in 1825 but it was first publically announced in 1826 by Balard and so the discovery is therefore credited to the French chemist and pharmacist Antoine-Jerome Balard.

Cadmium - the atomic number is 48 and the chemical symbol is Cd. The name derives from the Greek kadmeia for "calamine (zinc carbonate)" with which it was found as an impurity in nature. Kadmeia was also the name of the fortress of Thebes, a city in the Boeottia region of central Greece. The fortress was named after its founder, Cadmus, who was the son of the Phoenician king, Agenor, and brother of Europ and would be a possible source for the name of the ore. The element was discovered and first isolated by the German physician Friedrich Stromeyer in 1817.

Caesium - the atomic number is 55 and the chemical symbol is Cs. The internationally accepted name is caesium because it is derived from caesius but the name is often given in english as cesium. The name caesium derives from the Latin caesius for "sky blue color", which was the color of the caesium line in the spectroscope. It was discovered by the German chemist Robert Wilhelm Bunsen and the German physicist Gustav Robert Kirchhoff in 1860. It was first isolated by the German chemist Carl Setterberg in 1882.

Calcium - the atomic number is 20 and the chemical symbol is Ca. The name derives from the Latin calx for "lime (CaO) or limestone (CaCO3)" in which it was found. It was first isolated by the British chemist Humphry Davy in 1808 with help from the Swedish chemist Jons Jacob Berzelius and the Swedish court physician M.M. of Pontin, who had prepared calcium amalgam.

Californium - the atomic number is 98 and the chemical symbol is Cf. The name derives from the state and the university of California, where the element was first synthesized. Although the earlier members of the actinide series were named in analogy with the names of the corresponding members of the lanthanide series, the only connection with the corresponding element dysprosium (Greek for hard to get at) that was offered by the discoverers was that searchers for another element (gold about a century before in 1849) found it difficult to get to California. An American scientific team at the University of California lab in Berkeley, California under Glenn T. Seaborg used the nuclear reaction 242Cm( 4He, n) 245Cf to first detect the element californium in 1950. The longest half-life associated with this unstable element is 900 year 251Cf.

Carbon - the atomic number is 6 and the chemical symbol is C. The name derives from the Latin carbo for "charcoal". It was known in prehistoric times in the form of charcoal and soot. In 1797, the English chemist Smithson Tennant proved that diamond is pure carbon.

Cerium - the atomic number is 58 and the chemical symbol is Ce. The name, which was originally cererium but was shortened to cerium, derives from the planetoid Ceres, which was discovered by the Italian astronomer Guiseppe Piazzi in 1801 and named for Ceres, the Roman goddess of agriculture. Two years later in 1803, the element was discovered by the German chemist Martin-Heinrich Klaproth, who called the element ochroite because of its yellow color. This rare earth was independently discovered at the same time by the Swedish chemist Jons Jacob Bezelius and the Swedish minerologist Wilhelm von Hisinger, who called it ceria. It was first isolated in 1875 by the American mineralogist and chemist William Frances Hillebrand and the American chemist Thomas H. Norton.

Chlorine - the atomic number is 17 and the chemical symbol is Cl. The name derives from the Greek chlooros for "pale green or greenish yellow color" of the element. It was discovered by the Swedish pharmacist and chemist Carl-Wilhelm Scheele in 1774. In 1810, the English chemist Humphry Davy proved it was an element and gave it the name chlorine.

Chromium - the atomic number is 24 and the chemical symbol is Cr. The name derives from the Greek chroma for "color", from the many colored compounds of chromium. It was discovered in 1797 by the French chemist and pharmacist Nicolas-Louis Vauquelin. Vauquelin also isolated chromium in 1798.

Cobalt - the atomic number is 27 and the chemical symbol is Co. The name derives from the German kobold for "evil spirits or goblins", who were superstitiously thought to cause trouble for miners, since the mineral contained arsenic which injured their health and the metallic ores did not yield metals when treated with the normal methods. The name could also be derived from the Greek kobalos for "mine". Cobalt was discovered in 1735 by the Swedish chemist Georg Brandt.

Copper - the atomic number is 29 and the chemical symbol is Cu. The name derives from the Latin Cuprum for "Cyprus", the island where the Romans first obtained copper. The chemical symbol, Cu, also comes from the Latin cuprum. The element has been known since prehistoric times.

Curium - the atomic numberis 96 and the chemical symbol is Cm. The name derives from "Pierre and Marie Curie", the French physicist and Polish-born French chemist, who discovered radium and polonium. It was first synthesized in 1944 by the American scientists at the University of California lab in Berkeley, California under the American chemist Glenn T. Seaborg, using the nuclear reaction 239Pu( 4He, n) 242Cm. Since it is the ninth member of the actinide series, curium was named in analogy with its homologue the ninth member of the lanthanide series, gadolinium, which had been named after the Finnish rare earth chemist Johan Gadolin. The longest half-life associated with this unstable element is 15.6 million year 247Cm.

Dubnium - the atomic number is 105 and the chemical symbol is Db. The name derives from the location of the Russian research center, the Joint Institute for Nuclear Research lab in "Dubna", Russia. The first synthesis of this element is jointly credited to the American scientific team at the University of California in Berkeley, California under Albert Ghiorso and the Russian scientific team at the JINR (Joint Institute for Nuclear Reactions) lab in Dubna, Russia, under Georgi N. Flerov in 1970. The longest half-life associated with this unstable element is 34 second 262Db.

Dysprosium - the atomic number is 66 and the chemical symbol is Dy. The name derives from the Greek dysprositos for "hard to get at", due to the difficulty in separating this rare earth element from a holmium mineral in which it was found. Discovery was first claimed by the Swiss chemist Marc Delafontaine in the mineral samarskite in 1878 and he called it philippia. Philippia was subsequently found to be a mixture of terbium and erbium. Dysprosium was later discovered in a holmium sample by the French chemist Paul-Emile Lecoq de Boisbaudron in 1886, who was then credited with the discovery. It was first isolated by the French chemist George Urbain in 1906.

Einsteinium - the atomic number is 99 and the chemical symbol is Es. The name derives from "Albert Einstein", the Geituan born physicist who proposed the theory of relativity. A collaboration of American scientists from the Argonne National Laboratory near Chicago, Illinois, the Los Alamos Scientific Laboratory in Los Alamos, New Mexico and at the University of California lab in Berkeley, California first found 252Es in the debris of thermonuclear weapons in 1952. The longest half-life associated with this unstable element is 472 day 252Es.

Darmstadtium - the atomic number is 110 and the chemical symbol is Ds. The name derives from Darmstadt, the region where the research center GSI is located. This element was first synthesized in a November 1994 experiment by a multi-national team of scientists working at the Gesellschaft fur Schwerionenforschung (GSI) in Darmstadt, Germany. The scientific teams were from the GSI (Heavy Ion Research Center), Daiinstadt, the Joint Institute for Nuclear Research (JINR), Dubna, Russia, Comenius University, Bratislava, Slovakia and the University of Jyvaskyla, Finland. They used the nuclear reaction 208Pb( 62Ni, n) 269110. The longest half-life associated with this unstable element is 1.1 minute 281110.

Element 111 - no name has been proposed or accepted by IUPAC for element 111. This element was first synthesized in a December 1994 experiment by a multi-national team of scientists working at the GSI (Heavy Ion Research Center) in Darmstadt, Germany. The scientific teams were from GSI, Darmstadt, Germany, JINR, Dubna, Russia, the Comenius University in Bratislava, Slovakia and the University of Jyvaskyla, Finland. They used the nuclear reaction 209Bi( 64Ni, n) 272111. The longest half-life associated with this unstable element is 0.015 second 272111.

Element 112 - no name has been proposed or accepted by IUPAC for element 112. This element was first synthesized in a February 1996 experiment by a multi-national team of scientists working at the GSI (Heavy Ion Research Center) in Darmstadt, Germany. The scientific teams were from GSI, Darmstatdt, the Joint Institute for Nuclear Research (JINR), Dubna, Russia, the Comenius University in Bratislava, Slovakia and the University of Jyvaskyla, Finland. The teams used the nuclear reaction 208Pb( 70Zn, n) 277112. The longest half-life associated with this unstable element is 11 minute 285112.

Element 114 - no name has been proposed or accepted by IUPAC for element 114. This element was first synthesized in a November-December 1998 experiment by a multi-national team of scientists working at the Joint Institute for Nuclear Research (JINR), Dubna, Russia. The scientific teams were from JINR and the Lawrence Livermore Laboratory in Livermore, California, USA. The teams used the nuclear reaction 244Pu( 48Ca, 3n) 289114. The longest half­life associated with this unstable element is 21 second 289114.

Element 116 - no name has been proposed or accepted by IUPAC for element 116. This element was first synthesized in a July 2000 experiment at the Joint Institue for Nuclear Research (JINR), Dubna, Russia by a group of Russian scientists from JINR and a group of American scientists from the Lawrence Livermore Laboratory (LNL) in Livermore, California, USA. The group used the nuclear reaction 248Cm ( 48Ca, 4n) 292116. The longest half-life associated with this unstable element is 0.03 second 292116.

Element 118 - the claim of discovery of this element in Apri11999 has subsequently been withdrawn in 2001.

Erbium - the atomic number is 68 and the chemical symbol is Er. The name derives from the Swedish town of "Ytterby" (about 3 miles from Stockholm), where the ore gadolinite (in which it was found) was first mined. It was discovered by the Swedish surgeon and chemist Carl-Gustav Mosander in 1843 in an yttrium sample. He separated the yttrium into: yttrium, a rose colored salt he called terbium and a deep yellow peroxide that he called erbium. In 1860, an analysis of yttrium by the German chemist Berlin found only the yttrium and the rose colored salt, which was now called erbium not terbium. All subsequent workers followed Berlin in designating the rose colored rare earth as erbium.

Europium - the atomic number is 63 and the chemical symbol is Eu. The name derives from the continent of "Europe". It was separated from the mineral samaria in magnesium-samarium nitrate by the French chemist Eugene-Anatole Demarcay in 1896. It was also first isolated by Demarcay in 1901.

Fermium - the atomic number is 100 and the chemical symbol is Fm. The name derives from the Italian born physicist "Enrico Fermi", who built the first man made nuclear reactor. The nuclide ... Fm was found in the debris of a thermonuclear weapon's explosion in 1952 by a collaboration of American scientists from the Argonne National Laboratory near Chicago, Illinois, the Los Alamos Scientific Laboratory in Los Alamos, New Mexico and the University of California lab at Berkeley, California. The longest half-life associated with this unstable element is 100 day 257Fm.

Fluorine - the atomic number is 9 and the chemical symbol is F. The name derives from the Latin fluere for "flow or flux" since fluorspar (CaF2) was used as a flux in metallurgy because of its low melting point. It was discovered in hydrofluoric acid by the Swedish pharmacist and chemist Carl-Wilhelm Scheele in 1771 but it was not isolated until 1886 by the French pharmacist and chemist Ferdinand-Frederic-Henri Moisson.

Francium - the atomic number is 87 and the chemical symbol is Fr. The name derives from the country "France", where the French physicist Marguerite Perey from the Curie Institute in Paris, France discovered it in 1939 in the alpha particle decay of actinium, 227Ac -> 4He -> 223Fr, which was known as actinium-K and has a half-life of 22 minutes. An earlier claim of discovery in 1930 with the element name Virginium was determined to be incorrect. A similar claim for discovery of the element with atomic number 87 and named moldavium was also determined to be incorrect. The longest half-life associated with this unstable element is 22 minute 223Fr.

Gadolinium - the atomic number is 64 and the chemical symbol is Gd. The name derives from the mineral gadolinite, in which it was found, and which had been named for the Finnish rare earth chemist "Johan Gadolin". It was discovered by the Swiss chemist Jean-Charles Galissard de Marignac in 1886, who produced a white oxide he called Yα in a samarskite mineral. In 1886, the French chemist Paul-Emile Lecoq de Boisbaudran gave the name gadolinium to Yα.

Gallium - the atomic number is 31 and the chemical symbol is Ga. The name derives from the Latin gallia for "France" or perhaps from the Latin gallus for "le coq or cock", since it was discovered in zinc blende by the French chemist Paul-Emile Lecoq de Boisbaudan in 1875. It was first isolated in 1878 by Lecoq de Boisbaudran and the French chemist Emile-Clement Jungflesch. This element had previously been predicted as "eka-aluminum" by Mendeleev, along with its properties and its location in the Periodic Table.

Germanium - the atomic number is 32 and the chemical symbol is Ge. The name derives from the Latin gennania for "Germany". It was discovered and isolated by the German chemist, Clemens-Alexander Winkler in 1886 in the mineral argyrodite (GeS2.4Ag2S). This element had previously been predicted as "eka-silicon" by Mendeleev, along with its properties and its location in the Periodic Table.

Gold - the atomic number is 79 and the chemical symbol is Au. The name derives from the Sanskit jval to shine, the Teutonic word gulth for shining metal and the Anglo-Saxon gold of unknown origin. The chemical symbol Au derives from the Latin aurum, for Aurora the Goddess of dawn. It was known and highly valued in prehistoric times.

Hafnium - the atomic number is 72 and the chemical symbol is Hf The name derives from the Latin hafnia for "Copenhagen". An element named celtium was erroneously claimed to have been discovered in 1911 by the French chemist George Urbain in rare earth samples, until the Danish physicist Nils Bohr, predicted hafnium's properties using his theory of electronic configuration of the elements. Bohr argued that hafnium would not be a rare earth element but would be found in zirconium ore. It was discovered shortly thereafter by the Dutch physicist Dirk Coster and the Hungarian physicist Georg von Hevesy in 1923, while working at Bohr's institute in Copenhagen, Denmark.

Hassium - the atomic number is 108 and the chemical symbol is Hs. The name derives from the Latin Hassia for the German "state of Hesse", whose former capital was Darmstadt. The element was first synthesized by German physicists at the GSI (Center for Heavy-Ion Research) Lab at Darmstadt, Germany in 1984 using the nuclear reaction 208Pb( 58Fe, n) 265Hs. The longest half-life associated with this unstable element is 11 minute 277Hs.

Helium - the atomic number is 2 and the chemical symbol is He. The name derives from the Greek helios for "sun". The element was discovered by spectroscopy during a solar eclipse in the sun's chromosphere by the French astronomer Pierre-Jules-Cesar Janssen in 1868. It was independently discovered and named helium by the English astronomer Joseph Norman Lockyer. It was thought to be only a solar constituent until it was later found to be identical to the helium in the uranium ore cleveite by the Scottish chemist William Ramsay in 1895. Ramsay originally called his gas krypton, until it was identified as helium. The Swedish chemists Per Theodore Cleve and Nils Abraham Langet independently found helium in cleveite at about the same time.

Holmium - the atomic number is 67 and the chemical symbol is Ho. The name derives from the Latin holmia for "Stockholm". It was discovered in erbia earth by the Swiss chemist J. L. Soret in 1878, who referred to it as element X. It was later independently discovered by the Swedish chemist Per Theodor Cleve in 1879. It was first isolated in 1911 by Holmberg, who proposed the name holmium either to recognize the discoverer Per Cleve, who was from Stockholm or perhaps to establish his own name in history.

Hydrogen - the atomic number is 1 and the chemical symbol is H. The name derives from the Greek hydro for "water" and genes for "forming", since it burned in air to form water. It was discovered by the English physicist Henry Cavendish in 1766.

Indium - the atomic number is 49 and the chemical symbol is In. The name derives from indigo for the "indigo-blue" line in the element's spark spectrum. It was discovered in 1863 by the German physicist Ferdinand Reich and the German metallurgist Hieronymus Theodor Richter, while examining zinc blende. They isolated indium in 1867.

Iodine - the atomic number is 53 and the chemical symbol is I. The name derives from the Greek ioeides for "violet colored" because of its violet vapors. It was discovered in sea weed ash (kelp) by the French chemist Bernard Courtois in 1811. It was named iodine by the English chemist Humphry Davy in December 1813 and subsequently was named iode by the French chemist Louis-Joseph Gay-Lussac, when he proved it was an element in 1814. Dispite the priority rights dispute between Davy and Gay-Lussac, both acknowledged Courtois as the discoverer of the element.

Iridium - the atomic number is 77 and the chemical symbol is Ir. The name derives from the Latin Iris, the greek goddess of rainbows because of the "variety of colors in the element's salt solutions". Iridium and osmium were both discovered in a crude platinum ore in 1803 by the English chemist Smithson Tennant. Iridium was discovered independently by the French chemist H. V. Collet-Descotils also in 1803. Descotils actually published one month before Tennant but Tennent is given credit for the discovery, perhaps because he alone also found osmium in the ore.

Iron - the atomic number is 26 and the chemical symbol is Fe. The name derives from the Anglo­Saxon "iron" of unknown origin. The element has been known from prehistoric times. The chemical symbol Fe is derived from the Latin ferrum for "firmness".

Krypton - the atomic number is 36 and the chemical symbol is Kr. The name derives from the Greek kryptos for "concealed or hidden". It was discovered in liquified atmospheric air by the Scottish chemist William Ramsay and the English chemist Morris William Travers in 1898.

Lanthanum - the atomic number is 57 and the chemical symbol is La. The name derives from the Greek lanthanein for "to be hidden or to escape notice" because it hid in cerium ore and was difficult to separate from that rare earth mineral. It was discovered by the Swedish surgeon and chemist Carl-Gustav Mosander in 1839. In 1842, Mosander separated his lanthanium sample into two oxides; for one of these he retained the name lanthanum and for the other he gave the name didymium (or twin).

Lawrencium - the atomic number is 103 and the chemical symbol is Lr. The original chemical symbol was proposed as Lw but it was changed because "W" is an unusual occurrence in many languages and it is a cumbersome spoken word. The name derives from the American physicist "Ernest 0. Lawrence", who developed the cyclotron. Credit for the first synthesis of this element in 1971 is given jointly to American chemists from the University of California laboratory in Berkeley, California under Albert Ghiorso and the Russian scientific team at the JINR (Joint Institute for Nuclear Reactions) lab in Dubna, Russia under Georgi N. Flerov, after a series of preliminary papers presented over a decade. The longest half-life associated with this unstable element is 3.6 hour 262Lr.

Lead - the atomic number is 82 and the chemical symbol is Pb. The name derives from the Angol-Saxon lead, which is of unknown origin. The element was known from prehistoric times. The chemical symbol Pb is derived from the Latin plumbum for "lead".

Lithium - the atomic number is 3 and the chemical symbol is Li. The name derives from the Latin lithos for "stone" because lithium was thought to exist only in minerals at that time. It was discovered by the Swedish mineralogist Johan August Arfwedson in 1818 in the mineral petalite LiAl (S1205)2. It was isolated in 1855 by the German chemist Robert Wilhelm Bunsen and Augustus Matthiessen.

Lutetium - the atomic number is 71 and the chemical symbol is Lu. The name was originally "lutecium" but in 1949, IUPAC's CNIC changed the "c" to "t" since the name derives from "lutetia", the ancient Latin name for the city of "Paris", rather than from its French equivalent "lutece". The discovery is credited to the French chemist George Urbain in 1907 although it had been separated earlier and independently by the Austrian chemist Carl Auer von Welsbach from an ytterbium sample. Auer von Welsbach named the element cassiopeium for the constellation "Cassiopeia". Although Auer von Welsbach's paper appeared prior to the Urbain paper, Urbain argued that he had sent his paper to the editor earlier. The International Committee on Atomic Weights (where Urbain was one of the four members) adopted Urbain's name and his claim of priority. The German Atomic Weights' Committee accepted Auer von Welsbach's name of cassiopeia for the element for the next forty years. Urbain's name for the element was officially adopted by IUPAC's CNIC in 1949 based on consideration of prevailing usage, finally ending the controversy.

Magnesium - the atomic number is 12 and the chemical symbol is Mg. The name originally used was magnium and was later changed to magnesium, which is derived from Magnesia, a district in the northeastern region of Greece called Thessalia. The Scottish chemist Joseph Black recognized it as a separate element in 1755, In 1808, the English chemist Humphry Davy obtained the impure metal and in 1831 the French pharmacist and chemist Antoine-Alexandre Brutus Bussy isolated the metal in the pure state.

Manganese - the atomic number is 25 and the chemical symbol is Mn. The name derives from the Latin magnes for "magnet" since pyrolusite (Mn02) has magnetic properties. It was discovered by the Swedish pharmacist and chemist Carl-Wilhelm Scheele in 1774. Also in 1774, the Swedish chemist Johan Gottlieb Gahn first isolated the metal.

Meitnerium - the atomic number is 109 and the chemical symbol is Mt. The name derives from the Austrian physicist "Lise Meitner", who had discovered the element, protactinium. The first synthesis of the element Meitnerium is credited to German physicists from the GSI (Center for Heavy-Ion Research) lab at Darmstadt, Germany under Gunther Munzenberg, in 1982 using the nuclear reaction 209Bi( 58Fe, n) 266Mt. The longest half-life associated with this unstable element is 0.07 second 268Mt.

Mendelevium - the atomic number is 101 and the chemical symbol is Md. The original chemical symbol proposed was My but this was changed in 1955. The element name derives from the Russian chemist "Dimitrii Mendeleev" who developed the Periodic Table of the chemical elements. Credit for the first synthesis of this element is given American chemists at the University of California lab in Berkeley, California under Glenn T. Seaborg in 1958, who used the nuclear reaction 253Es( 4He, 2n) 255Md and the nuclear reaction 253Es ( 4He, n) 256Md. The longest half-life associated with this unstable element is 51 day 258Md.

Mercury - the atomic number is 80 and the chemical symbol is Hg. The name derives from the Roman god "Mercury", the nimble messenger of the gods, since the ancients used that name for the element, which was known from prehistoric times. The chemical symbol, Hg, derives from the Greek hydragyrium for "liquid silver" or quick silver.

Molybdenum - the atomic number is 42 and the chemical symbol is Mo. The original name that was proposed was molydaenum but this was changed because of the prevailing usage of "e" rather than "ae" in English, American and French. Since the ending of the name was spelt "num" and not "nium" in most languages, this ending was not changed. The name derives from the Greek molybdos for "lead". The ancients used the term lead for any black mineral which leaves a mark on paper. It was discovered by the Swedish pharmacist and chemist Carl Wilhelm Scheele in 1778. It was first isolated by the Swedish chemist Peter-Jacob Hjelm in 1781.

Neodymium - the atomic number is 60 and the chemical symbol is Nd. The name was originally neodidymium and was later shortened to neodymium, which is derived from the Greek neos for "new" and didymos for "twin". It was discovered by the Swedish surgeon and chemist Carl Gustav Mosander in 1841 , who called it didymium (or twin) because of its similarity to lanthanium which he had previously discovered two years earlier. In 1885, the Austrian chemist Carl Auer von Welsbach separated didymium into two elements. One of which he called neodymium (or new twin).

Neon - the atomic number is 10 and the chemical symbol is Ne. The name derives from the Greek neos for "new". It was discovered from its bright red spectral lines by the Scottish chemist William Ramsay and the English chemist Morris William Travers in 1898 from a liquified air sample.

Neptunium - the atomic number is 93 and the chemical symbol is Np. The name derives from the planet "Neptune" ( the Roman god of the sea), since it is the next outer-most planet beyond the planet uranus in the solar system and this element is the next one beyond uranium in the periodic table.It was first synthesized by Edwin M. McMillan and Philip H. Abelson in 1940 via the nuclear reaction 238U( n, γ) 239U -> β- -> 239Np. The longest half-life associated with this unstable element is 2.14 million year 237Np.

Nickel - the atomic number is 28 and the chemical symbol is Ni. The name derives from the German nickel for "deceptive little spirit", since miners called mineral niccolite (NiAs) by the name kupfernickel (false copper) because it resembled copper ores in appearance but no copper was found in the ore. It was discovered by the Swedish metallurgist Axel-Fredrik Cronstedt in 1751.

Niobium - the atomic number is 41 and the chemical symbol is Nb. The name derives from the Greek mythological character "Niobe", who was the daughter of Tantalus (see the element tantalum), since the elements niobium and tantalum were originally thought to be identical elements. Niobium was discovered in a black mineral from America called columbite by the British chemist and manufacturer Charles Hatchett in 1801 and he called the element columbium, since the mineral was discovered in America. A year later in 1802, the element tantalum was discovered. In 1809, the English chemist William Hyde Wollaston claimed that the elements columbium and tantalum were identical. Forty years later, the Geiinan chemist and pharmacist, Heinrich Rose, determined from their acids that columbium and tantalum were two different elements in 1846 and gave the name niobium to columbium because it was so difficult to distinguish it from tantalum. Rose claimed that his niobium had a larger atomic weight than tantalum. Finally, in 1866, the Swiss chemist Jean-Charles Galissard de Marignac separated these elements. For more than a century, the name columbium continued to be used in America and niobium in Europe until IUPAC's CNIC adopted the name niobium in 1949 based on consideration of prevailing usage. Niobium was first isolated by the chemist C. W. Blomstrand in 1846.

Nitrogen - the atomic number is 7 and the chemical symbol is N. The name derives from the Latin nitrum and Greek nitron for "native soda" and genes for "forming" because of nitrogen's presence in potassium nitrate (KNO), so called salpeter or nitre or native soda. It was discovered by the Scottish physician and chemist Daniel Rutherford in 1772.

Nobelium - the atomic number is 102 and the chemical symbol is No. The name derives from "Alfred Nobel", the discoverer of dynamite and founder of the Nobel prizes. It was first synthesized in 1966 by the Russian scientists from the JINR (Joint Institute for Nuclear Research) lab in Dubna, Russia under Georgi Flerov. Earlier claims to have synthesized "Nobelium" beginning in 1957 were shown to be erroneous but the original name was retained because of its widespread use throughout the scientific literature. The longest half-life associated with this unstable element is 58 minute 259No.

Osmium - the atomic number is 76 and the chemical symbol is Os. The name derives from the Greek osme for "smell" because of the sharp odor of the volatile oxide. Both osmium and iridium were discovered simultaneously in a crude platinum ore by the English chemist Smithson Tennant in 1803.

Oxygen - the atomic number is 8 and the chemical symbol is O. The name derives from the Greek oxys for "acid" and genes for "forming", since the French chemist Antoine-Laurent Lavoisier originally thought that oxygen was an acid producer because by burning phosphorus and sulfur and dissolving them in water, he was able to produce acids. Oxygen was discovered independently by the Swedish pharmacist and chemist Carl-Wilhelm Scheele in 1771 and the English clergman and chemist Joseph Priestly in 1774. Scheele's "Chemical Treatise on Air and Fire" was delayed in publication until 1777, so Priestly is credited with the discovery, since he published first.

Palladium - the atomic number is 46 and the chemical symbol is Pd. The name derives from the second largest asteroid of the solar system Pallas (named after the goddess of wisdom and arts - Pallas Athene). The element was discovered by the English chemist and physicist William Hyde Wollaston in 1803, one year after the discovery of Pallas by the German astronomer H. W. M. Olbers in 1802. The discovery was originally published anonymously by Wollaston to obtain priority, while not disclosing any details about his preparation.

Phosphorus - the atomic number is 15 and the chemical symbol is P. The name derives from the Greek phosphoros for "bringing light", since white phosphorus oxidizes spontaneously in air and glows in the dark. This was also the ancient name for the planet Venus, when it appears before sunrise. It was discovered by the German merchant Hennig Brand in 1669.

Platinum - the atomic number is 78 and the chemical symbol is Pt. The name derives from the Spanish platina for "silver". In 1735, the Spanish mathematician Don Antonio de Ulloa found platinum in Peru, South America. In 1741, the English metallurgist Charles Wood found platinum from Columbia, South America. In 1750, the English physician William Brownrigg prepared purified platinum metal.

Plutonium - the atomic number is 94 and the chemical symbol is Pu. The name derives from the planet Pluto, (the Roman god of the underworld). Pluto was selected because it is the next planet in the solar system beyond the planet Neptune and the element plutonium is the next element in the period table beyond neptunium. Plutonium was first synthesized in 1940 by American chemists Glenn T. Seaborg, Edwin M. McMillan, Joseph W. Kennedy and Arthur C. Wahl in the nuclear reaction 238U( 2H, 2n) 238Np -> β- -> 238Pu. The longest half-life associated with this unstable element is 80 million year 244Pu.

Polonium - the atomic number is 84 and the chemical symbol is Po. This radioactive metal was also known as radium-F. The name derives from "Poland", the native country of Marie Sklodowska Curie. It was discovered by Pierre and Marie Curie in 1898, from its radioactivity. It was independently found by the German chemist Willy Marckwald in 1902 and called radio­tellurium. The longest half-life associated with this unstable element is 102 year 209Po.

Potassium - the atomic number is 19 and the chemical symbol is K. The name derives from the English "potash or pot ashes" since it is found in caustic potash (KOH). The chemical symbol K derives from the Latin kalium via the Arabic qali for alkali. It was first isolated by Humphry Davy in 1807 from electrolyosis of potash (KOH).

Praseodymium - the atomic number is 59 and the chemical symbol is Pr. The name was originally praseodidymium and was later shortened to praseodymium, which is derived from the Greek prasios for "green" and didymos for "twin" because of the pale green salts it focus. It was discovered by the Austrian chemist Carl Auer von Welsbach in 1885, who separated it and the element neodymium from a didymium sample. Didymium had previously been thought to be a separate element.

Promethium - the atomic number is 61 and the chemical symbol is Pm. The name promethium was preferred to prometheum because most metallic elements have names ending in "ium" and "eum" would have caused problems. The name derives from "Prometheus" who stole fire from heaven and gave it to the human race, since it was found by the harnessing of nuclear energy which also provides a dangerous threat of punishment. In 1926, there had been a claim of discovery of element 61 at the University of Illinois in the USA and the element was named illinium. Subsequently another claim was made that element 61 had actually been discovered in Italy in 1924 but the manuscript had been secretly stored in a sealed envelope with Academia dei Lincei and the element had been named Florentium. Both elements were supposedly found in natural minerals. It was later shown that this element does not exist in nature and both of these claims were discarded. In 1941, neodymium and praseodymium were irradiated with neutrons, deuterons and alpha particles at Ohio State University in the USA and new activities were produced. Some of these activities are now associated with element 61. However, no chemical proof of element 61 was available because rare earth elements could not be separated from each other at that time. Promethium was first synthesized in fission products from the the thermal neutron fission of 235U at the Clinton (later Oak Ridge National Laboratory) lab by the American chemists, J. A. Marinsky, L. E. Glendenin and Charles D. Coryell in 1947, using chemical separation by ion exchange chromotography. The fission products, 147Pm and 149Pm were also identified in the slow neutron activation of neodymium. The longest half-life associated with this unstable element is 17.7 year 145Pm.

Protactinium - the atomic number is 91 and the chemical symbol is Pa. The name was originally prototactinium but in 1949 it was shortened to protactinium by IUPAC's CNIC. The name derives from the Greek protos for "first" and actinium, since it was found to be the parent of actinium. An isotope of protactinium, 234Pa, was first identified by the German chemists Kasimir Fajans and O. H. Gohring in 1913. They named the element "Brevium" because of its short half­life. The longer half-lived isotope, 231Pa, was identified by the German chemist Otto Hahn and the Austrian physicist Lise Meitner in 1918, while Hahn was away in military service. It was first isolated by the German chemist Aristid V. Grosse in 1927. Protactinium was accepted as the name for the element because it was preferred to use the name of the longer-lived isotope. The longest half-life associated with this unstable element is 32.5 thousand year 231Pa.

Radium - the atomic number is 88 and the chemical symbol is Ra. The name derives from the Latin radius for "beam or ray" because of its tremendous ray-emitting power. It was discovered by the French physicist Pierre Curie and the Polish-born, French chemist Marie Sklodowska Curie in 1898. It was independently discovered by the British chemists Frederick Soddy and John A. Cranston. It was first isolated in 1910 by Marie Curie and the French chemist Andre­Louis Debierne. The longest half-life associated with this unstable element is 1599 year 226Ra.

Radon - the atomic number is 86 and the chemical symbol is Rn. The name indicates its origin from radium. It had first been called radium emanation or just emanation (with chemical symbol Em) because it was a decay product of radium. Ramsay next suggested the name "niton" (with chemical symbol Nt), which is Latin for shining. It was finally changed to radon in 1923. Radon was discovered in 1900 by the German chemist Friedrich Ernst Dorn and it was first isolated in 1910 by the Scottish chemist William Ramsay and the English chemist Robert Whytlaw-Gray. The longest half-life associated with this unstable element is 3.8 day 222Rn.

Rhenium - the atomic number is 75 and the chemical symbol is Re. The name derives from the Latin rhenus for "the Rhine river in Germany". It was discovered by x-ray spectroscopy in 1925 by the German chemists, Walter Noddack, Ida Tacke and Otto Berg.

Rhodium - the atomic number is 45 and the chemical symbol is Rh. The name derives from the Greek rhodon for rose because of the "rose color of dilute solutions of its salts". It was discovered by the English chemist and physicist William Hyde Wollaston in 1803 in a crude platinum ore.

Rubidium - the atomic number is 37 and the chemical symbol is Rb. The name derives from the Latin rubidus for deepest red because of the two "deep red lines" in its spectra. It was discovered in the mineral lepidolite by the German chemist Robert Wilhelm Bunsen and the German physicist Gustav-Robert Kirchoff in 1861. Bunsen isolated rubidium in 1863.

Ruthenium - the atomic number is 44 and the chemcial symbol is Ru. The name derives from the Latin ruthenia for the "old name of Russia". It was discovered in a crude platinum ore by the Russian chemist Gottfried Wilhelm Osann in 1828. Osann thought that he had found three new metals in the sample, pluranium, ruthenium and polinium.He later withdrew his claim of discovery. In 1844 the Russian chemist Karl Karlovich Klaus was able to show that Osann's mistake was due to the impurity of the sample but Klaus was able to isolate the ruthenium metal and he retained Osann's original name of ruthenium.

Rutherfordium - the atomic number is 104 and the chemical symbol is RE The name derives from the English physicist "Ernest Rutherford" who won the Nobel prize for developing the theory of radioactive transformations. Credit for the first synthesis of this element is jointly shared by American scientists at the University of California lab in Berkeley, California under Albert Ghiorso and by Russian scientists at the JINR (Joint Institute for Nuclear Reactions) lab in Dubna, Russia under Georgi N. Flerov. The longest half-life associated with this unstable element is 10 minute 263Rf.

Samarium - the atomic number is 62 and the chemical symbol is Sm. The name derives from the mineral Samarskite, in which it was found and which had been named for "Colonel von Samarski", a Russian mine official. It was originally discovered in 1878 by the Swiss chemist Marc Delafontaine, who called it decipium. It was also discovered by the French chemist Paul­Emile Lecoq de Boisbaudran in 1879. In 1881, Delafontaine determined that his decipium could be resolved into two elements, one of which was identical to Boisbaudran's samarium. In 1901, the French chemist Eugene-Anatole Demarcay showed that this samarium earth also contained europium.

Scandium - the atomic number is 21 and the chemical symbol is Sc. The name derives from the Latin scandia for "Scandinavia", where the mineral were found. It was discovered by the Swedish chemist Lars-Fredrik Nilson in 1879 from an ytterbium sample. In the same year, the Swedish chemist Per Theodore Cleve proved that scandium was Mendeleev's hypothetical element "eka­boron", whose properties and position in the Periodic Table Mendeleev had previously predicted.

Seaborgium - the atomic number is 106 and the chemical symbol is Sg. The name derives from the American chemist "Glenn Theodore Seaborg", who led a team that first synthesized a number of transuranium elements. The element Seaborgium was first synthesized by American scientists from the University of California lab in Berkeley, California under Albert Ghiorso, who used the nuclear reaction 249Cf( 18O, 4n) 263Sg. The longest half-life associated with this unstable element is 21 second 266Sg.

Selenium - the atomic number is 34 and the chemical symbol is Se. The name derives from the Greek Selene, who was the Greek goddess of the moon because the element is chemically found with tellurium (Tellus - the Roman goddess of the earth). It was discovered by the Swedish chemist Jons Jacob Berzelius in 1817, while trying to isolate tellurium in an impure sample.

Silicon - the atomic number is 14 and the chemical symbol is Si. The name was originally silicium because it was thought to be a metal. When this was shown to be incorrect, the name was changed to silicon, which derives from the Latin silex and silicis for "flint". Amorphous silicon was discovered by the Swedish chemist Jons Jacob Berzelius in 1824. Crystalline silicon was first prepared by the French chemist Henri Sainte-Claire Deville in 1854.

Silver - the atomic number is 47 and the chemical symbol is Ag. The name derives from the Anglo-Saxon seofor and siolfur, which is of unknown origin. The chemical symbol, Ag, derives from the Latin argentum and Sanskrit argunas for "bright". The element was known in prehistoric times.

Sodium - the atomic number is 11 and the chemical symbol is Na. The name derives from the English soda and Latin sodanum for "headache remedy". The chemical symbol Na derives from the Latin natrium for "natron (soda in english)". It was discovered in 1807 by the English chemist Humphry Davy from electrolyosis of caustic soda (NaOH).

Strontium - the atomic number is 38 and the chemical symbol is Sr. The name derives from Strontian, "a town in Scotland". The mineral strontianite is found in mines in Strontian. The element was discovered by the Scottish chemist and physician Thomas Charles Hope in 1792 observing the brilliant red flame color of strontium. It was first isolated by the English chemist Humphry Davy in 1808.

Sulfur - the atomic number is 16 and the chemical symbol is S. The American name sulfur was preferred to the English name sulphur because many languages have a spelling using an "f 'and the origin of the name is obscure. The name derives from the Latin sulfurium or sulphurium and the Sanskrit sulveri. Sulfur was known as brenne stone for "combustible stone" from which brim-stone is derived. It was known from prehistoric times and thought to contain hydrogen and oxygen. In 1809, the French chemists, Louis-Joseph Gay-Lussac and Louis-Jacques Thenard proved the elemental nature of sulfur.

Tantalum - the atomic number is 73 and the chemical symbol is Ta. The name derives from the Greek "Tantalos", for the mythological character who was banished to Hades, the region of lost souls where he was placed up to his chin in water, which receded whenever he tried to drink it and under branches of fruit, which drew back whenever he tried to pick their fruit. This name was selected because of the insoluability of tantalum in acids, thus when placed in the midst of acids it is incapable of taking any of them up. It was discovered by the Swedish chemist and mineralogist Anders-Gustav Ekeberg in 1802 (see Niobium).

Technetium - the atomic number is 43 and the chemical symbol is Tc. The name derives from the Greek technetos for "artificial". The claims of discovery of this element are extensive. It was first thought to be found in platinum ores in 1828 and was named polinium but it was actually impure iridium. In 1846 an element ilmenium was claimed to be found in minerals and after further work, the author claimed another element neptunium (not to be confused with element 93). Ilmenium was determined to be impure niobium. In 1847, pelopium was claimed as a new element but it was also found to be impure niobium. In 1877, a new element, davyum (in honor of Humphry Davy) was claimed in platinum ore but it was determined to be a mixture of iridium, rhodium and iron. In 1896, anew element lucium was claimed to be found but it was determined to be yttrium. In 1909, the element nipponium was claimed to be isolated from various minerals but the claim was never substantiated and it is now argued to be element 75 (rhenium) and not element 43 (technetium). Finally, in 1925, the element masurium was claimed to be found in platinum ores by Ida Noddack-Tacke, Walter Noddack and Otto Berg. They were not able to isolate weighable amounts of the element, so their claim was also never verified. Technetium was first synthesized in 1937 by Italian physicists Carlo Perrier and Emilio Segre from the Royal University of Palermo in a molybdenum sample, which was bombarded with deuterons (2H) to produce 95mTc and 97mTc, using the reactions 94Mo(d,n)95mTc and 96Mo(d,n)97mTc. The longest half-life associated with this unstable element is 6.6 million year 98Tc.

Tellurium - the atomic number is 52 and the chemical symbol is Te. The name derives from the Latin Tellus, who was the "Roman goddess of the earth". It was discovered by the Roumanian mine director Franz Joseph MUller von Reichenstein in 1782 and overlooked for sixteen years until it was first isolated by German chemist Martin-Heinrich Klaproth in 1798. The Hungarian chemist Paul Kitaibel independently discovered tellurium in 1789, prior to Klaproth's work but after von Reichenstein.

Terbium - the atomic number is 65 and the chemical symbol is Tb. The name derives from the "village of Ytterby" in Sweden, where the mineral ytterbite (the source of terbium) was first found. It was discovered by the Swedish surgeon and chemist Carl-Gustav Mosander in 1843 in an yttrium salt, which he resolved into three elements. He called one yttrium, a rose colored salt he called terbium and a deep yellow peroxide he called erbium. The chemist Berlin detected only two earths in yttrium, i.e., yttrium and the rose colored oxide he called erbium. In 1862, the Swiss chemist Marc Delafontaine reexamined yttrium and found the yellow peroxide. Since the name erbium had now been assigned to the rose colored oxide, he initially called the element mosandrum (after Mosander) but he later reintroduced the name terbium for the yellow peroxide. Thus the original names given to erbium and terbium samples are now switched. Since Bunsen spectroscopically examined Mosander's erbium (now terbium) sample and declared that it was a mixture, the question of who actually discovered terbium, Mosander or Delafontaine remains unresolved to this day.

Thallium - the atomic number is 81 and the chemical symbol is TI. The name derives from the Greek thallos for "green shoot or twig" because of the bright green line in its spectrum. It was discovered by the English physicist and chemist William Crookes in 1861. The metal was first isolated by the French chemist Claude-Auguste Lamy in 1862.

Thorium - the atomic number is 90 and the chemical symbol is Th. The name derives from Thor, the "Scandanavian god of thunder". It was discovered in the mineral thorite (ThSiO4) by the Swedish chemist Jons Jacob Berzelius in 1828. It was first isolated by the chemists D. Lely Jr. and L. Hamburger in 1914.

Thulium - the atomic number is 69 and the chemical symbol is Tin. The name derives from Thule, the earliest name for the northern most part of the civilized world - "Scandanavia (Norway, Sweden and Iceland)". It was discovered in 1879 by the Swedish chemist Per Theodor Cleve in a sample of erbium mineral. It was first isolated by the American chemist Charles James in 1911.

Tin - the atomic number is 50 and the chemcial symbol is Sn. The name derives from the Anglo­Saxon tin of unknown origin. The chemical symbol, Sn, is derived from the Latin stannum for alloys containing lead. The element was known in prehistoric times.

Titanium - the atomic number is 22 and the chemical symbol is Ti. The name derives from the Latin titans, who were the mythological "first sons of the earth". It was originally discovered by the English clergyman William Gregor in the mineral ilmenite (FeTi03) in 1791. He called this iron titanite menachanite for the Menachan parish where it was found and the element menachin. It was rediscovered in 1795 by the German chemist Martin Heinrich Klaproth, who called it titanium because it had no characteristic properties to use as a name. Titanium metal was first isolated by the Swedish chemists Sven Otto Pettersson and Lars Fredrik Nilson.

Tungsten - the atomic number is 74 and the chemical symbol is W. The name derives from the Swedish tung sten for "heavy stone". The chemical symbol, W, is derived from the German wolfram, which was found with tin and interferred with the smelting of tin. It was said to eat up tin like a wolf eats up sheep. In 1949, IUPAC's CNIC officially adopted wolfram as the scientific name for the element and reserved tungsten for the commercial name, similar to the use of iron and steel. By 1951, the chemical community erroneously thought that the name tungsten had been eliminated. A world-wide protest resulted in the CNIC reverting back to the name tungsten pending a further review, which has never occurred. The element was discovered by the Swedish phaiinacist and chemist Carl-Wilhelm Scheele in 1781. Tungsten metal was first isolated by the Spanish chemists Don Fausto d'Elhuyar and his brother Don Juan Jose d'Elhuyar in 1783.

Uranium - the atomic number is 92 and the chemical symbol is U. The name derives from the planet Uranus, which in Roman mythology was "Father Heaven". The German chemist Martin­Heinrich Klaproth discovered the element in 1789, following the German/English astronomer William Hershel's discovery of the planet in 1781. The metal was first isolated by the French chemist Eugene-Melchior Peligot in 1841.

Vanadium - the atomic number is 23 and the chemical symbol is V. The name derives from the "Scandanavian goddess of love and beauty", Freyja Vanadis, because of its many beautiful multicolored compounds. It was discovered by the Swedish physician and chemist Nils-Gabriel Sefstrom in 1830. It had originally been discovered by the Spanish mineralogist Andres Manuel del Rio y Fernandez in 1801, who named it erythronium, after the plant of that name whose flowers have many beautiful colors. Del Rio later decided that it was really chromium in his lead sample, however his lead sample was later shown to have vanadium in it. Vanadium metal was first isolated by the English chemist Henry Enfield Roscoe in 1869.

Xenon - the atomic number is 54 and the chemical symbol is Xe. The name derives from the Greek xenon for "the stranger". It was discovered by the Scottish chemist William Ramsay and the English chemist Morris William Travers in 1898 in a liquified air sample.

Ytterbium - the atomic number is 70 and the chemical symbol is Yb. The name derives from the "Swedish village of Ytterby", where the mineral ytterbite (the source of ytterbium) was originally found. It was discovered by the Swiss chemist Jean-Charles Galissard de Marignac in 1878 in erbium nitrate from gadolinite (ytterbite renamed). In 1907, Carl Auer von Welsbach determined that ytterbium was actually two elements, which he named aldebaranium and cassiopeium. At the same time and independently, George Urbain obtained two elements from ytterbium, which he named neoyterbium and lutecium. Urbain's name of neoyyterbium was accepted over Auer von Welsbach' name of aldebaranium. The name was later shortened back to ytterbium. (See the discussion of the Urbain and Auer von Welsbach priority dispute under lutetium).

Yttrium - the atomic number is 39 and the chemical symbol is Y. The name of this element originally given by Gadolin was ytterbium and it was later shortened to yttrium by Anders­Gustav Eckberg. The name derives from the "Swedish village of Ytterby", where the mineral gadolinite was found. In 1794, the Finnish chemist Johan Gadolin discovered yttrium in the mineral ytterbite, which was later renamed gadolinite for Gadolin. Later another element was given the name ytterbium that Gadolin had proposed. The Swedish surgeon and chemist Carl­Gustav Mosander separated the element in 1843.

Zinc - the atomic number is 30 and the chemical symbol is Zn. The name derives from the German zink of unknown origin. It was first used in prehistoric times, where its compounds were used for healing wounds and sore eyes and for making brass. It was recognized as a metal as early as 1374.

Zirconium - the atomic number is 40 and the chemical symbol is Zr. The name derives from the Arabic zargun for "gold-like". It was discovered in zirconia by the German chemist Martin­Heinrich Klaproth in 1789. Zirconium was first isolated by the Swedish chemist Jons Jacob Berzelius in 1824 in an impure state and finally by the chemists D. Lely Jr. and L. Hamburger in a pure state in 1914.(http://www.nndc.bnl.gov/)

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