3. Atoms & Molecules
Dalton’s Atomic Theory
On the basis of laws of chemical combination John Dalton, an English school teacher in Manchester, proposed that behaviour of matter could be explained using an atomic theory. He published his work about atomic theory in 1808. The main points of Dalton’s atomic theory are:
All the matter is made up of very small particles called “atoms”.
Atoms cannot be divided.
Atoms can neither be created nor destroyed.
Atoms are of various kinds. There are as many kinds of atoms as are elements
All the atoms of a given element are identical in every respect, having the same mass, size and chemical properties.
Atoms of different elements differ in mass, size and chemical properties.
Chemical combination between two (or more) elements consists in the joining together of atoms of these elements to form molecules of compounds.
The “number” and “kind” of atoms in a given compound is fixed.
During chemical combination, atoms of different elements combine in small whole numbers to form compounds.