Chemistry Atomic Structure and Radioactivity part-1

Dalton's Atomic Theory

John Dalton (1890) put forward the first theory about the structure of the matter. Its main postulates are

`=>` Atom can neither be created nor be destroyed.

`=>` Matter consists of indivisible atoms.

`=>` All the atoms of a given chemical element are identical in mass and in all other properties.

`=>` Different chemical elements have different kinds of atoms and in particular such atoms have different masses.

`=>` The formation of a compound from its elements occurs through the combination of atoms of unlike elements in small whole number ratio.

Drawbacks of Dalton's Atomic Theory

`=>` It does not explain why atoms of different elements differ in their mass, valencies etc.
`=>` It does not explain how and why atoms of elements combine with each other to form molecules.
`=>` It does not explain the existence of isotopes and isobars.

Constitution of Atom

A series of investigations that began in the 1850s and extended into the twentieth century clearly demonstrated that atoms actually possess an internal structure, i.e. they are made up of even smaller particles, which are called subatomic particles. These are electron, proton and neutron.