Activity: 1.8


1
How do you calculate valency of an element from its electronic configuration?

Ans:
The number of electrons present in the outermost shell are known as the valence electrons. The valency of an element depends on valence electrons.
e.g. The atomic number of Magnesium (Mg) is 12. Thus, its electronic configuration is 2, 8, 2. If magnesium gives away these ywo electrons, its outermost shell becomes stable. Hence, the valency of Magnesium is 2.

2
What is the valency of elements with atomic number 8, 14, 17 and 20?

Ans:
Atomic Number
Electronic Configuration
Valence Electrons
Valency
8
2, 6
6
2
14
2, 8, 4
4
4
17
2, 8, 7
7
1
20
2, 8, 8, 2
2
2

3
How does valency vary in a period and in a group?


Ans:
  • All the elements in the same group have the same number of valence electrons. Hence, elements in the same group have same valency.
  • As we move from left to right in a period, the valency gradually increases from 1 to 4 and then gradually decreases from 4 to 0.