Chemical element
The periodic table of the chemical elements
A chemical element is a pure chemical substance con-
sisting of one type of atom distinguished by its atomic
number, which is the number of protons in its nucleus.
The term is also used to refer to a pure chemical sub-
stance composed of atoms with the same number of pro-
tons.[1] Common examples of elements are iron, copper,
silver, gold, hydrogen, carbon, nitrogen, and oxygen. In
total, 117 elements have been observed as of 2008, of
which 94 occur naturally on Earth. 80 elements have
stable isotopes, namely all elements with atomic num-
bers 1 to 82, except elements 43 and 61 (technetium and
promethium). Elements with atomic numbers 83 or
higher (bismuth and above) are inherently unstable, and
undergo radioactive decay. The elements from atomic
number 83 to 94 have no stable nuclei, but are neverthe-
less found in nature, either surviving as remnants of the
primordial stellar nucleosynthesis which produced the
elements in the solar system, or else produced as short-
lived daughter-isotopes through the natural decay of
uranium and thorium.[2]
All chemical matter consists of these elements. New
elements of higher atomic number are discovered from
time to time, as products of artificial nuclear reactions.
History
Several old philosophies used a set of archetypal classic-
al elements to explain patterns in nature. The term ’ele-
ment’ was originally used to refer to a state of matter
(solid/earth, liquid/water, gas/air, and plasma/fire) or a
phase of matter (as in the Chinese Wu Xing), rather than
the chemical elements of modern science. The Greek, In-
dian (Tattva and Mahābhūta) and Japanese (go dai) tradi-
tions essentially had the same five elements: Air, Earth,
Fire, Water and Aether.
The term ’elements’ (stoicheia) was first used by the
Greek philosopher Plato in about 360 BCE, in his dia-
logue Timaeus, which includes a discussion of the
Mendeleev’s 1869 periodic table
composition of inorganic and organic bodies and is a
rudimentary treatise on chem