CBSE Class 12 Chemistry Notes: The p Block Elements – Nitrogen Family (part II)

GENERAL TRENDS IN PHYSICAL PROPERTIES

Illustration 1.
Name three allotropes of phosphorous? Which of the three is most reactive?
Solution: White or yellow, red and black. White phosphorus is most reactive.

CHEMICAL PROPERTIES OF GROUP 15
As we move down the group there is a decrease in covalent character.
N > P > As > Sb > Bi
Nitrogen is chemically less reactive, due to high stability of its molecule, N₂ in which two nitrogen atoms are combined through triple covalent bonds (N ≡ N) from which one is sigma (σ) and two are pie (π) bonds, thus posses high bond strength (941.4 KJ mol^-1).

Nitrogen has one special feature that it can form pπ – pπ multiple bonds with itself, carbon and oxygen due to its small size. In phosphorus rather pπ – pπ, dπ – pπ is found as in POX₃

1. Hydrides

All elements of this group form gaseous hydrides of the type MH3. The stability however decreases down the group for these hydrides.

All the hydrides are strong reducing agents and reacts with metal ions to give phosphides, arsenides or antimonides. Phosphine and other hydrides of heavier members of this groups are highly poisonous.

Structure of Hydrides

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