Atoms

An atom is the smallest particle of an element that has the properties of that element.

There have been various models that have been proposed to describe the structure of the atom.

• Billiard ball model - John Dalton
• Plum pudding model - J.J. Thomson
• Nuclear model - E. Rutherford
• Shell model of the atom - N. Bohr
• The quantum model of the atom - various scientists.

The atom consists of three subatomic particles. The proton, the neutron and the electron.

In a chemical reaction all the action takes place in the outer or valence shell of electrons.

Molecules

What is a molecule? A molecule is a group of atoms that joined together by a covalent bond.