Dalton’s Atomic Theory

After the above two laws of chemical combination were put forward, the next problem faced by scientist was to give appropriate explanation of these laws. This led John Dalton to put forward a theory in 1808 about the nature of matter. Dalton picked up the idea of divisibility of matter, which was till then just a theoretical idea. The theory is based on certain postulates called postulates (or assumptions) of Dalton’s atomic theory. His theory provided an explanation for the law of conservation of mass and the law of definite proportion. According to Dalton’s atomic theory all matter, whether an element, a compound or a mixture is composed of small particles called atoms.

POSTULATES OF DALTON’S ATOMIC THEORY:

• All the matter is made up of very small particles called “atoms”.
• Atoms cannot be divided.
• Atoms can neither be created nor be destroyed.
• Atoms are of various kinds. There are as many kinds of atoms as are elements.
• All the atoms of 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 consist of the joining together of atoms of chemical 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.
• Atoms of the same elements can combine in more than one ratio to form more than one compound.