Give differences between an atom and an ion.

Give Reasons for the Following:

The atoms of elements such as helium, neon, argon, radon, etc., do not form ions easily. Why is it so?

Give Reasons for the Following:

Why valency of an element is considered very important?

Differentiate between the cation and an anion.

What is meant by:

(a) Molecular mass

(b) Chemical formula

(c) Mole