Question

The atomic number and the mass number of certain elements are given below in the table.

Element	A	B	C	D	E	F
Atomic number	1	3	8	18	20	1
Mass	2	7	16	40	40	4

(i) Select a pair of isobar and isotope from the above table. 

(ii) What would be the valency of elements B and E?

Answer 1

(i) Pair of isotope are A and F because they have the same atomic number. 

Pair of isobar are D and E because they have the same mass number. 

(ii) Valency of element B can be determined by electronic configuration, for the element B is 2, 1. The valency is 1. 

Electronic configuration for E is 2, 8, 8, 2. So the valency is 2.