In 1897, English physicist J. J.
Thomson (1856–1940) disproved Dalton’s idea that atoms are
indivisible. When elements were excited by an electrical current, atoms
break down into two parts. One of those parts is a negative tiny
particle, which Thomson called a corpuscle in 1881. The term
electron was introduced in 1891 by G. Johnstone Stoney
(1826-1911) as a way to describe a “natural unit of electricity.”
Thomson envisioned these negative charges embedded into
positive charges, like an English plum pudding. The plums were the
electrons and the pudding was the positive matter.
Thomson's idea of an atom did not
survive very long. English physicist Ernest Rutherford
(1871–1937) studied the effects of bombarding thin gold foil with
alpha particles. Alpha particles are helium atoms that have
lost their electrons and are positive. Rutherford’s model had a
nucleus, which occupied a very small area toward the middle, and was
positive. He used the term proton for the positive particles.
However, his electrons were moving on the outside of the nucleus in no
definable manner in his model.
A is Dalton's Model; B is Thomson;
and C is Ruthford's model of an atom