Question

Define valency by taking examples of silicon and oxygen.
[3 Marks]

Answer 1

Valency of an element is defined as the number of electrons gained/lost/shared by an atom to achieve the octet configuration. In other words, valency can be defined as the combining capacity of that element.

If the number of valence electrons of the atom is less than or equal to four, then the valency of that element is equal to the number of valence electrons.
On the other hand, if the number of valence electrons of the atom is greater than four, then the valency of that element is obtained by subtracting the number of valence electrons from eight.
[2 Marks]

For example, the atom of silicon has 4 valence electrons, since its atomic number is 14 and electronic configuration is 2, 8, 4.
Thus, the valency of silicon is four.
[0.5 Marks]

Moreover, the atom of oxygen has 6 valence electrons, since its atomic number is 8 and electronic configuration is 2, 6.
Thus, the valency of oxygen is 8 - 6 = 2.
[0.5 Marks]