Question

Based on the group valency of elements write the molecular formula of the following
compounds giving justification for each (i) Oxidenof group 1 (ii) Hallides of group 13 (iii)
Compound formed when Element A of group 3 combines with an Element B of Group 17

Answer 1

Answer:

Explanation:

(i) The first group elements have a common valency of 1 and the valency of oxygen is 2 and to satisfy the combining capacity of oxygen, 2 elements of first group are required. Thus the oxide of the first group elements have the common formula of M  

2

​  

O.

Ex- Na  

2

​  

O,K  

2

​  

O,etc.

(ii) The valency of group 13 elements is 1 and the valency of oxygen is 2 and to satisfy the combining capacity of group 13 elements, 3 of halogens are required. Thus the molecular formula will be of form MX  

3

​  

.

Ex- AlCl  

3

​  

,BF  

3

​  

,etc.

(iii) The valency of group 2 elements is 2 and that of group 17 is 1. Thus two elements of group 17 are required to combine with group 2 element.

Ex- MCl  

2

​  

,CaCl  

2

​  

,etc.