Question

Define the term valency. Arrange the following elements in order of increasing valency:

Aluminium, Sodium, Carbon, Nitrogen and Oxygen.

Answer 1

Valency:

• The combining capacity of an element is called valency.
• The number of electrons present in the outermost shell is called the valence electrons and they determine the valency of the element.

A short-cut method is used to calculate valency :

• If the number of valence electrons is less than or equal to 4, then valency = valence electrons.
• If the number of valence electrons is more than 4, then valency = 8 - valence electrons.

So, for the given elements:

Element	Atomic number	Electronic configuration	Valency
Aluminium	13	2,8,3	3
Sodium	11	2,8,1	1
Carbon	6	2,4	4
Nitrogen	7	2,5	3
Oxygen	8	2,6	2

So, increasing the order of valency will be:

Sodium ($\mathrm{Na}$)< Oxygen ($\mathrm{O}$)<Aluminium ($\mathrm{Al}$)< Nitrogen ($\mathrm{N}$)< Carbon ($\mathrm{C}$).