Atom
SMALLEST UNIT OF A CHEMICAL ELEMENT
Atoms; Atomic chemical; Atom and Atomic Theory; Atomic structure; Polyelectronic atoms; Bound-bound; Bound-bound transition; Structure of the atom; Multielectron atom; Ancient atom; Chemical atom; Chemical Atom; Number of atoms on Earth; Polyelectronic; Monoelectronic; Atomic system
The ultimate particle or division of an elementary substance; the
smallest part that can exist in combination, and one which cannot exist
alone. An elementary substance is composed of molecules just as truly as
a compound one, but the atoms in the molecule of an elementary substance
are all precisely alike. Hence atoms are the units of chemistry, they
have to do with combinations, but the physical unit, the smallest
particle of matter that can have an independent existence, is the
molecule. The two are often confounded, especially by writers of a few
years ago, so that by "atom" the molecule is often meant. There is
nothing to be said of their size or mass. All such calculations refer to
the molecule, q. v., often spoken of and called the atom.
[Transcriber's note: Yet to be discovered: electron--1897 (5 years),
proton--1920 (28 years), neutron--1932 (30 years), quark--1961 (69
years).]