What are the key points in Dalton's atomic theory

Dalton's theory was based on the premise that the atoms of different could be distinguished by differences in their weights. He stated his theory in a lecture to the Royal Institution in 1803. The theory proposed a number of basic ideas:

1. Elements are made of extremely small particles called atoms.
2. Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties.
3. Atoms cannot be subdivided, created, or destroyed.
4. Atoms of different elements combine in simple whole-number ratios to form chemical .
5. In chemical reactions, atoms are combined, separated, or rearranged.

Using his theory, Dalton rationalised the various laws of chemical combination which were in existence at that time. However, he made a mistake in assuming that the simplest compound of two elements must be binary, formed from atoms of each element in a 1:1 ratio, and his system of atomic weights was not very accurate - he gave oxygen an atomic weight of seven instead of eight. Despite these errors, Dalton's theory provided a logical explanation of concepts, and led the way into new fields of experimentation.