Every substance is made up of elements, and each element is made up of similar, minute particles called atoms. This chapter traces atomic theories from Dalton to Thomson, the discovery of the electron, proton and neutron, and then valency, ions, chemical formulae, chemical equations and the laws of chemical combination.
1. Elements and Atoms
- 118 elements are identified so far: 92 occur in nature (e.g. Copper, Iron, Gold, Silver) and the rest are synthesised in laboratories (e.g. Technetium, Promethium, Neptunium, Plutonium).
- The word atom is derived from the Greek word atomos.
- The Greek philosopher Democritus and the Tamil poet Avvaiyar spoke of atoms, but without a scientific base.
- The first scientific theory about the atom was given by John Dalton, followed by J.J. Thomson and Rutherford.