Question

When chlorine atom becomes chloride ion,its size increases...why?

Answer 1

Because it acquires an electron so it's radius increases.

Answer 2

Chlorine is a highly negative ion.

When chlorine atom accepts an electron the repulsion between the electrons increases (Like charges(-) repels each other).

As all electrons repel the size of the ion is found to be increased than that of the original atom.

As number of atoms increases the repulsion increases and so the size also increases.