chemistry chemical reaction
In the compound SO3, Oxygen can have -1 or -2 valence values, and S can have -1, -2, +2, +4 or +6 values but since there are three Oxygen molecules and one Sulfur molecule, each Oxygen molecule must have a value of -2 (total of -6) and each Sulfur molecule a value of +6 to balance to zero (-6 +6 = 0).
Valency of Sulphur (S) = +6 and Oxygen (O) = -2
Therefore, O4 = -2 x 4 = -8
Hence, valency of SO4 = Valency of sulphur + valency of oxygen
= +6 + (-8) = -2
Thus, valency of SO4 is 2.
Valency of any atom is the maximum number of valence electrons that can be shared by the concerned atom .
In Nitrogen , valence shell contain 5 electrons , so maximum valency of Nitrogen can be 5 .Now ,the number of electrons shared by nitrogen in ammonia is 3 only , with 3 hydrogen and remaining two electrons remain as a lone pair . So , electrons shared by nitrogen is 3 , and hence , valency of Nitrogen in ammonia is 3 .