Sub-atomic particles

Sub-atomic particles

Dalton thought that atoms were solid, indivisible particles. However, because of work done mainly by Lord Rutherford, the idea has been greatly changed in recent years. According to Rutherford, the atom consists of three kinds of particles.

1. Protons
2. Neutrons

Early atomic models

1. J.J. Thomson discovered the electron and proposed the "plum pudding" model: a positively charged sphere with negative electrons spread throughout.
2. Ernest Rutherford discovered that:
   • The nucleus is the atom's central core and contains protons.
   • Most of an atom's mass is in the nucleus.
   • Electrons orbit the nucleus and have very small mass.
   • Atoms are mostly empty space.
   • He proposed the planetary model of the atom.
3. James Chadwick later discovered the neutron, a neutral particle in the nucleus.

Properties of sub-atomic particles

Properties of sub-atomic particle	Symbol	Charge	Location	Relative mass	Real mass (g)
Electron	e⁻	−1	Outside the nucleus	1/1840	9.109 × 10⁻²⁸
Proton	p	+1	In the nucleus	1	1.673 × 10⁻²⁴
Neutron	n	0	In the nucleus	1	1.675 × 10⁻²⁴