NCERT Question 7 - Chapter 4 Class 9 - Structure of Atom

Define valency by taking examples of silicon and oxygen.

Answer

• Valency is the combining capacity of an atom.

(i) Silicon

• Atomic number = 14
• Number of electrons = Atomic number = 14
• Electronic configuration of silicon is 2,8,4
• Hence, the valence shell has 4 e -
• It has equal chance of gaining, losing or sharing it's valence electrons in order to achieve octet 
• In any case the valency of silicon = 4

(ii) Oxygen  

• Atomic number = 8

• Number of electrons = Atomic number = 8
• Electronic configuration of Oxygen is 2,6
• Hence, the valence shell has 6 e -
• If an atom has 6 electrons in its valence shell, it is easier for them to gain 2 e- to achieve an octet

• Therefore, valency of oxygen = 2