History of the atom

Democritus argued that there are various basic elements which always existed but can be rearranged into many different forms and that all matter is made up of small indivisible particles called atoms.

John Dalton supported the theory of Democritus that all matter was made of small indivisible particles called atoms, but unlike Democritus, Dalton supported his theory with evidence.

In 1805 Dalton proposed the following:

- All matter consists of indivisible particles;
- Atoms of a particular element have an identical mass and chemical properties;
- Atoms can not be created or destroyed during chemical reactions;
- Compounds are the result of the combination of two or more elements whose proportion is fixed;
- Atoms combine in simple numerical ratios.

In 1897 Thomson took the latest evidence of the existence of negative and positive particles present in the atom and came up with his plum pudding model of the atom.
He imagined the atom to consist of a sphere of positive matter in which negative particles were randomly embedded much like plums in a pudding.