Question

What is difference between valency and charge of an atom?

Answer 1

Valency is the number of electrons that need to be added or removed from outermost shell of an atom to complete its octate or satisfy the octate rule.
Charge is the value attained by the atom after removal or addition of electron/s. Only those ions are stable which satisfy the octate rule.
Valency is defined for atoms (neutral species) while charge for ions(charged species).
Ex. Valency of sodium atom is 1 and charge on it is zero. Charge on sodium ion is 1 and its valency is zero.