Chemical element

History

The term 'elements' (stoicheia) was first used by the Greek philosopher Plato in about 360 BCE, in his dialogue Timaeus, which includes a discussion of the composition of inorganic and organic bodies and is a rudimentary treatise on chemistry. Plato assumed that the minute particle of each element corresponded to one of the regular polyhedra: tetrahedron (fire), octahedron (air), icosahedron (water), and cube (earth).^[3]

Tetrahedron (fire)	Octahedron (air)	Icosahedron (water)	Cube (earth)

Adding to the quintessence", which formed the heavens. Aristotle defined an element as:

Element – one of those bodies into which other bodies can be decomposed and which itself is not capable of being divided into other.^[4]

Building on this theory, in c. 790 Arabian chemist Jabir ibn-Hayyan (Geber) postulated that metals were formed out of two elements: sulphur, ‘the stone which burns’, which characterized the principle of combustibility, and mercury, which contained the idealized principle of metallic properties.^[5] Shortly thereafter, this evolved into the Arabic concept of the three principles: sulphur giving flammability or combustion, mercury giving volatility and stability, and salt giving solidity.

In 1524, Swiss chemist Paracelsus adopted Aristotle’s four element theory, but reasoned that they appeared in bodies as Geber’s three principles. Paracelsus saw these principles as fundamental, and justified them by recourse to the description of how wood burns in fire. Mercury included the cohesive principle, so that when it left in smoke the wood fell apart. Smoke represented the volatility (the mercury principle), the heat-giving flames represented flammability (sulphur), and the remnant ash represented solidity (salt).^[5]

In 1669, German physician and chemist Johann Becher published his Physica Subterranea. In modification on the ideas of Paracelsus, he argued that the constituents of bodies are air, water, and three types of earth: terra fluida, the mercurial element, which contributes fluidity and volatility; terra lapida, the solidifying element, which produces fusibility or the binding quality; and terra pinguis, the fatty element, which gives material substance its oily and combustible qualities.^[6] These three earths correspond with Geber’s three principles. A piece of wood, for example, according to Becher, is composed of ash and terra pinguis; when the wood is burnt, the terra pinguis is released, leaving the ash. In other words, in combustion the fatty earth burns away.

In 1661, periodic table, shown below, there were sixty-six elements.

From Boyle until the early 20th century, an element was defined as a pure allotropes.

By 1919, there were seventy-two known elements.^[8] In 1955, element 101 was discovered and named mendelevium in honor of Mendeleev, the first to arrange the elements in a periodic manner. In October 2006, the synthesis of element 118 was reported; however, element 117 has not yet been created in the laboratory.

Description

The lightest elements are nuclear fission.

As of 2006, there are 117 known elements (in this context, "known" means observed well enough, even from just a few decay products, to have been differentiated from any other element).^[10][11] Of these 117 elements, 94 occur naturally on Earth. Six of these occur in extreme trace quantities: californium, have been detected in the universe at large, in the spectra of stars and also supernovae, where short-lived radioactive elements are newly being made.

The remaining 22 elements not found on Earth or in astronomical spectra have been derived artificially. All of the solely-artificially derived elements are radioactive with very short Technetium was the first purportedly non-naturally occurring element to be synthesized, in 1937, although trace amounts of technetium have since been found in nature, and the element may have been discovered naturally in 1925. This pattern of artificial production and later natural discovery has been repeated with several other radioactive naturally-occurring trace elements.

Lists of the elements periodic table, which groups elements with similar chemical properties together.

Atomic number

The isotopes of the element.

The number of protons in the atomic nucleus also determines its atomic weight) is considered the identifying characteristic of an element.

Atomic mass

The mass number of an element, A, is the number of nucleons (protons and neutrons) in the atomic nucleus. Different isotopes of a given element are distinguished by their mass numbers, which are conventionally written as a super-index on the left hand side of the atomic symbol (e.g., ²³⁸U).

The atomic mass unit (u). This number may be a fraction which is not close to a whole number, due to the averaging process. On the other hand, the atomic mass of a pure isotope is quite close to its mass number. Whereas the mass number is a natural (or whole) number, the atomic mass of a single isotope is a real number which is close to a natural number. In general, it differs slightly from the mass number as the mass of the protons and neutrons is not exactly 1 u, the electrons also contribute slightly to the atomic mass, and because of the nuclear binding energy. For example, the mass of ¹⁹F is 18.9984032 u. The only exception to the atomic mass of an isotope not being a natural number is ¹²C, which has a mass of exactly 12, due to the definition of u (it is fixed as 1/12th of the mass of a free carbon-12 atom, exactly).

Isotopes

chemistry is a mixture of ^{12C, 13C, and 14C atoms.}

All three of the isotopes of carbon have the same chemical properties. But they have different nuclear properties. In this example, carbon-12 and carbon-13 are stable atoms, but radioactive, decaying over time into other elements.

Like carbon, some atomic numbers greater than 82.

Allotropes

Some elements can be found as multiple elementary substances, known as fullerenes, which have nearly spherical shapes. The ability for an element to exist in one of many structural forms is known as 'allotropy'.

Standard state

The enthalpy of formation of zero in its standard state. For example, the reference state for carbon is graphite, because it is more stable than the other allotropes.

Nomenclature

The naming of elements precedes the atomic theory of matter, although at the time it was not known which chemicals were elements and which compounds. When it was learned, existing names (e.g., gold, mercury, iron) were kept in most countries, and national differences emerged over the names of elements either for convenience, linguistic niceties, or nationalism. For example, the Germans use "Wasserstoff" for "hydrogen" and "Sauerstoff" for "oxygen", while English and some romance languages use "sodium" for "natrium" and "potassium" for "kalium", and the French, Greeks and Poles prefer "azote/azot" for "nitrogen".

But for international trade, the uranium-235.

In the second half of the twentieth century physics laboratories became able to produce nuclei of chemical elements that have a half life too short for them to remain in any appreciable amounts. These are also named by IUPAC, which generally adopts the name chosen by the discoverer. This can lead to the controversial question of which research group actually discovered an element, a question which delayed the naming of elements with atomic number of 104 and higher for a considerable time. (See element naming controversy).

Precursors of such controversies involved the nationalistic namings of elements in the late nineteenth century. For example, niobium originally named it columbium, in reference to the New World. It was used extensively as such by American publications prior to international standardization.

Chemical symbols

For the listing of current and not used List of elements by symbol.

Specific chemical elements

Before chemistry became a science, John Dalton devised his own simpler symbols, based on circles, which were to be used to depict molecules.

The current system of chemical notation was invented by antimony.

Chemical symbols are understood internationally when element names might need to be translated. There are sometimes differences; for example, the Germans have used "J" instead of "I" for iodine, so the character would not be confused with a roman numeral.

The first letter of a chemical symbol is always capitalized, as in the preceding examples, and the subsequent letters, if any, are always lower case (small letters).

General chemical symbols

There are also symbols for series of chemical elements, for comparative formulas. These are one capital letter in length, and the letters are reserved so they are not permitted to be given for the names of specific elements. For example, an "X" is used to indicate a variable group amongst a class of compounds (though usually a ligand in inorganic and organometallic chemistry. "M" is also often used in place of a general metal.

Isotope symbols

The three main isotopes of the element tritium. This is in order to make it easier to use them in chemical equations, as it replaces the need to write out the mass number for each atom. It is written like this:

D₂O (heavy water)

Instead of writing it like this:

²H₂O

Abundance

Main article: Abundance of the chemical elements

During the early phases of the Big Bang, nucleosynthesis of hydrogen nuclei resulted in the production of hydrogen and helium isotopes, as well as very minuscule amounts (on the order of 10^-10) of lithium and beryllium. No heavier elements were produced. As a result, the primordial abundance of atoms consisted of roughly 75% ¹H, 25% ⁴He, and 0.01% intergalactic space can still closely resemble the primordial abundance, unless it has been enriched by some means.

The following table shows the ten most common elements in our galaxy (estimated spectroscopically), as measured in parts per million, by mass.^[14] Nearby galaxies that have evolved along similar lines have a corresponding enrichment of elements heavier than hydrogen and helium. The more distant galaxies are being viewed as they appeared in the past, so their abundances of elements appear closer to the primordial mixture. As physical laws and processes appear common throughout the visible universe, however, it is expected that these galaxies will likewise have evolved similar abundances of elements.

Element	Parts per million by mass
Hydrogen	739,000
Helium	240,000
Oxygen	10,700
Carbon	4,600
Neon	1,340
Iron	1,090
Nitrogen	970
Silicon	650
Magnesium	580
Sulfur	440

Recently discovered elements

The first ununoctium, which was successfully synthesized on October 9, 2006, by the Flerov Laboratory of Nuclear Reactions in Dubna, Russia.^[15][16]

Element 117, ununseptium, has not yet been created or discovered, although its place in the periodic table is preestablished, and likewise for possible elements beyond 118.

See also

References

Chemical information

• WebElements
• Chemicool
• ChemicalElements
• Los Alamos National Laboratorybe-x-old:Хімічны элемэнт