Chemical element





A chemical element (sometimes called simply element) is a material that
consists of atoms with the same number of protons in the nucleus. This
number is known as the atomic number of the element. For example, all atoms
with 6 protons in their nuclei are atoms of the chemical element carbon, and
all atoms with 92 protons in their nuclei are atoms of the element uranium.

Lists of the elements by name, by symbol, and by by atomic number are
available. The most convenient presentation of the elements is in the
periodic table, which groups elements with similar chemical properties together.

Atoms of the same element whose nuclei contain a different number of
neutrons are said to be different isotopes of the element. A pure element
can exist as monoatomic units or as diatomic or polyatomic units comprising
the same kind of atoms. These are called allotropes, irrespective of the state.

The official names of the chemical elements are decided by the International
Union of Pure and Applied Chemistry who generally adopt the name chosen by
the discoverer. This can lead to the controversial question of which
research group did actually discover an element, and question which delayed
the naming of elements with atomic number of 104 and higher for a
considerable time. Chemical elements are also given a unique chemical
symbol, often based on the name of the element,not necessarily in English
(for example, carbon has chemical symbol 'C', and sodium has chemical symbol
'Na' after the Latin natrium). Chemical symbols are understood
internationally when element names might need to be translated. A chemical
symbol is always capitalized, as in the preceding examples, unlike the full
name of the element, which is never capitalized, even if it is derived from
a proper noun, unless it begins a sentence.

Elements can combine (react) to form pure compounds (such as water, salts,
oxides and organic compounds). In many cases these compounds have
essentially one fixed stoichiometry (composition) and their own structure
and properties.

Some -particularly metallic- elements combine to form new structures with a
more variable composition (such as metal alloys) in that case it is better
to speak of phases rather than compounds.

In general, a particular chemical can consist of a mixture of all of the above.