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:
- Elements are made of extremely small particles called atoms.
- Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties.
- Atoms cannot be subdivided, created, or destroyed.
- Atoms of different elements combine in simple whole-number ratios to form chemical .
- 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.
