Dalton's atomic theory

Dalton's atomic theory 

The theory that all matters is made up of very tiny indivisible particles (atoms) is called atomic theory of matter. Dalton put forward his atomic theory of matter in 1808.

      The various postulates or assumptions of Dalton's atomic theory of matter are as follows-

(1) All the matter is made up of very tiny particles called atoms.

(2) Atoms cannot be divided.

(3) Atoms can neither be created nor be destroyed.

(4) Atoms are of various kinds. There are as many kinds of atoms as are elements.

(5) All the atoms of a given element are identical in every respect, having the same mass, size and chemical properties.

(6) Atoms of different elements differ in mass, size and chemical properties.

(7) Chemical combination between two or more elements consists in the joining together of atoms of these elements to form molecules of compounds.

(8) The numbers and kind of atoms in a given compound is fixed.

(9) During chemical combination,atom a of different elements combine in small whole numbers to form compounds.

(10) Atoms of same elements can combine in more than one ratio to form more than one compound.

           Dalton's atomic theory was the first modern attempt to describe the behaviour of matter in terms of atoms. This theory was also used to explain the laws of chemical combination.

Drawbacks of Dalton's atomic theory-

 It is now known that some of the statement of  Dalton's atomic theory of matter are not exactly correct. Some of the drawbacks of the Dalton's atomic theory of matter are given below-

(1) one of the major drawback of Dalton's atomic theory  of matter is that atoms were thought to be indivisible ( which cannot be divided). We know that under special circumstances, atoms can be further divided into still smaller particles called electrons , protons and neutrons.

(2) Dalton's atomic theory says that all the atoms of an element have exactly the same mass. It is, however, now known that atoms of the same element can have slightly different masses.

(3) Dalton's atomic theory says that atoms of different elements have different masses. It is however now known that even atoms of different elements can have the same mass.

                John Dalton

 John Dalton was born in 1766 in a poor weaver's family in England. He received his early education from his father and at the village school. Dalton started teaching in the village at the age of 12 . In 1793 , Dalton left for Manchester to teach physics,chemistry and mathematics in a college. In 1794 , he described colour blindness. In 1808 , Dalton presented his atomic theory to explain the properties of matter. Dalton was the first to calculate the masses of the atoms of several elements. He died in 1844.