CBSE Class 12 Chemistry Notes: The p Block Elements

The elements of group 15 combines with oxygen directly or indirectly to form different types of oxides.

Oxidation state of central atom	N	P	As	Sb	Bi
+5	N₂O₅	P₄O₁₀	As₂O₅	Sb₂O₅	Bi₂O₅
+4	N₂O₄, NO₂	P₄O₈	–	–	–
+3	N₂O₃	P₄O₆	As₂O₃	Sb₂O₃	Bi₂O₃
+2	NO	–	–	–	–
+1	N₂O	–	–	–	–

Nature of oxides
All the oxides of nitrogen and phosphorus are strongly acidic in nature (except NO and N₂O); oxides of arsenic are weakly acidic; oxides of antimony are amphoteric and oxides of bismuth are weakly basic. This can be explained on the basis of increase in size of central atom. In lower element oxides, atom has small size and it can more strongly pulls the electron pair between O-H bond in water and thus helps in release of H+ ions.

Formation of oxides
1. Formation of oxides of nitrogen

2. Formation of oxides of phosphorus

The oxides of As(III) and Sb (III) can also be prepared by heating these elements in air.

3. Structures of oxides

Illustration 1.
The reddish brown coloured gas formed when nitric oxide is oxidized by air is
(A) N₂O₅ (B) N₂O₄
(C) NO₂ (D) N₂O₃
Solution: (C)

Illustration 2.
Which of the following oxides is the most acidic?
(A) N₂O₅ (B) P₂O₅
(C) As₂O₅ (D) Sb₂O₅
Solution: (A)