Subatomic Particles

John Dalton proposed (in 1808) that atom is the smallest indivisible particle of matter. Atomic radii are of the order of 10-8cm. It contain three subatomic particles namely electrons, protons and neutrons,

Electron

Electron was discovered as a result of study of cathode rays by JJ Thomson. It was named by Stony

It carries a unit negative charge (-1.6 * 10-19 C).

Mass of electron is 9.11 * 10-31 kg and mass of one mole of electron is 0.55 mg.

Some of the characteristics of cathode rays are:

These travel in straight line away from cathode and produce fluorescence when strike the glass wall of discharge tube.
These cause mechanical motion in a small pin wheel placed – their path.
These produce X-rays when strike with metal and are deflected by electric and magnetic field
Proton

Rutherford discovered proton on the basis of anode ray experiment.

It carries a unit positive charge (+1.6 * 10-19) C).

The mass of proton is 1.007276 U.

The e / m ratio of proton is 9.58 * 10-4 C / g. (e / m ratio is maximum for hydrogen gas.)

Some of the characteristics of anode rays are :

These travel in straight line and posses mass many times the mass of an electron.
These are not originated from anode.
These also cause mechanical motion and are deflected by electric and magnetic field.
Specific charge (e / m) for these rays depends upon the nature of the gas taken and is maximum for H2
Neutron

Neutrons are neutral particles. It was discovered by Chadwick (1932). The mass of neutron is 1.675x 10-24 g or 1.008665 amu or u.

94Be + 42He → 126C + 10n

Some Uncommon Subatomic Particles

(a) Positron Positive electron (0+1e), discovered by Dirac (1930) and Anderson (1932).

(b) Neutrino and antineutrino Particles of small mass and no charge as stated by Fermi (1934).

(c) Meson Discovered by Yukawa (1935) and Kemmer. They are unstable particles and include pi ions [pi;+, pi;– or pi;0].

(d) Anti-proton It is negative proton produced by Segre and Weigand (1955).