An atom is electrically neutral, and if it contains negatively charged electrons it must also contain

some positively charged particles, and the supposition that they existed within atoms came about

as a result of Rutherford's experiments in which he bombarded elements with the alpha - rays and

alpha - rays were given off by radioactive elements. The neutron was discovered in 1932 by James

Chadwick by bombarding beryllium with alpha rays.

The electron and proton have equal, but opposite, electric charges; the neutron is not charged.

The electron and proton have equal, but opposite, electric charges; the neutron is not charged.

The existence of electrons in atoms was first suggested, by J.J. Thomson, as a result of

experimental work on the conduction of electricity through gases at low pressures, which

produces cathode rays and x-rays, and a study of radioactivity by Becquerel, the Curies and

Rutherford.

Some of the important properties of the cathode rays studied by Sir J.J. Thomson and others are:

Cathode rays come out at right angles to the surface of the cathode and move in straight lines.

Their path is independent on the position of the anode.

They produce phosphorescence on certain salts like ZnS and fluorescence on glass.

They blacken photographic plates.

The rays pass through thin sheet of metals. If the metal sheet is too thick to be penetrated the

rays cast a shadow.

They produce X-ray when they strike a metal.