An electron is an elementary particle carrying a
unit charge of negative electricity. An atom consists
of a small, dense, positively charged nucleus surrounded
by electrons that whirl about it in orbits, forming
a cloud of charge.
Ordinarily there are just enough
negative electrons to balance the positive charge
of the nucleus, and the atom is neutral. If electrons
are added or removed, a net charge results, and the
atom is said to be ionized atomic electrons are responsible
for the chemical properties of matter (Valence).
electron was discovered in 1897 by Joseph John Thomson,
who showed that cathode rays are composed of electrons.
The electron is the lightest known particle having
a non-zero rest mass. The positron, the electron's
antiparticle was discovered in 1932.