Dalton’s Atomic Theory

Dalton’s Atomic Theory

John Dalton provided a basic theory about the nature of matter. He proposed a model of atom known as Dalton’s atomic theory in 1808 based on his experiments. The main postulates of Dalton’s atomic theory are:

• All the matters are made up of extremely small particles called atoms philosopher Democritus used thename for the smallest indivisible particles).

• Atoms of the same element are identicalin all aspects (size, shape, mass and properties).

• Atoms of different elements have different sizes and masses, and possess different properties.

• Atoms can neither be created nor be destroyed. i.e., atom is indestructible.

• Atoms of different elements may combine with each other in a fixed simple ratio to form molecules.

• An atom is the smallest particle of matter that takes part in a chemical reaction.

John Dalton, son of a poor weaver, began his career as a village school teacher at the age of 12. He became the principal of the school seven years later. In 1793, he moved to Manchester to teach Physics, Chemistry and Mathematics in a college. He proposed his atomic theory in 1803. He carefully recorded each day, the temperature, pressure and amount of rainfall from his youth till the end. He was a meticulous meteorologist.

Advantages of Dalton’s Atomic Theory

• Dalton’s theory explains most of the properties of gases and liquids.

• This explains the law of chemical combination and the law of conservation of mass (They are explained at the last section).

• This theory helps to recognize the molecular differences of elements and compounds.

Limitations of Dalton’s Atomic Theory

• Atom is no longer considered as the smallest indivisible particle.

• Atoms of the same element have different masses (Isotopes).

• Atoms of the different elements may have same masses (Isobars).

• Substances made up of same kind of atoms may have different properties (Ex. Coal, Graphite and Diamond are made up of carbon atoms but they differ in their properties