ELECTRON- In 1897, Sir J. J. Thomas, an English physicist, measured the
deflection of cathode-ray particles in magnetic and electrical fields. As a
result he found the ratio of the charge, e, to the mass, m, of the cathode-ray
particles. He found e/m identical to those particles irrespective of the metal
the electrodes were made of or the kind of gas in the tube. In 1909, RA
Millikan, an American scientist, measured that charge. All electrons are found
to be identical no matter their source or the method of liberating them from
matter. From the values of e/m, and e, the mass of an electron was calculated
to be .00055 amu.

PROTON- Eugeen Goldstein used a Crookes tube with holes in the cathode, and
observed that another kind of ray was emitted from the anode and passed through
the holes. He discovered this in 1886. In 1889, William Wien showed these rays
to be positively charged. The ratio of charge to mass was smaller than
electrons, but varied in different gasses. This meant that either charge varied,
mass varied or both varied. Both vary. Charge is equal to an electron, but
opposite in sign. Mass was smaller when used as a gas. From the values of e/m
for positive particles, m was calculated to be 1.0073 amu. This became known as
a proton.

NEUTRON- In 1932, James Chadwick detected the third of the basic parts of an
atom. He showed that uncharged particles, or neutrons, are emitted when atoms
of other elements are bombarded with high-velocity helium atoms with all
electrons remored, or an alpha particle. Neutrons were determined to have a
mass of 1.0087 amu. They are unstable outside of an atom and slowly degenerate
to form protons and electrons.

Category: Science