Dalton's Atomic Theory

When scientists started exploring matter, they realised that matter can be divided into smaller and still smaller particles. What was the ultimate particle like? They discovered that the smallest particle of an element that maintains its chemical identity through all chemical and physical changes is called and 'atom'.

John Dalton (1766 - 1844) can rightly be called the father of the Modern Theory on Atoms. He proposed his Atomic Theory in 1808, i.e., almost 200 years back. He did not have the help of sophisticated instruments that are available today to the scientists. Hence, many of his proposals, have been modified and updated. Over the years, substantial changes have taken place regarding the atomic theory, yet some of the assumptions that Dalton made are still held valid.

Dalton's Atomic Theory

John Daltons Atomic Theory provided a simple theory of matter to provide theoretical justification to the laws of chemical combinations in 1805. The basic postulates of the theory are:

• All substances are made up of tiny, indivisible particles called atoms.
• Atoms of the same element are identical in shape, size, mass and other properties.
• Each element is composed of its own kind of atoms. Atoms of different elements are different in all respects.
• Atom is the smallest unit that takes part in chemical combinations.
• Atoms combine with each other in simple whole number ratios to form compound atoms called molecules.
• Atoms cannot be created, divided or destroyed during any chemical or physical change.