CBSE Class 9 Answered

Bohr- Bury principle is also known as octet rule..

The octet rule  refers to the tendency of atoms to prefer to have eight electrons in their valence shell either by transfer (gaining or losing) of valence electrons from one atom to another or by sharing of valence electrons. When atoms have fewer than eight electrons, they tend to react to attain an octet configuration and form more stable compounds.

For example, (a) The formation of NaCl from sodium and chlorine according to octet rule.

The electronic configuration of chlorine is 2, 8, 7. So, chlorine (Cl) has 7 valence electrons. It will gain one electron (e.g. from sodium which loses one electron to form Na⁺) to form Cl^-, which has 8 valence electrons and so fulfills the octet rule and is stable.

Cl + e^-  ---> Cl ^–

2, 8, 7 2, 8, 8

The electronic configuration of sodium is 2, 8, 1. So by losing one electron to form Na⁺, sodium also attains octet configuration.

 Na ---->  Na⁺ + e^- 

2, 8, 1 2, 8

Na⁺ + Cl^- ---->  NaCl

(b) The formation of  CCl ₄ according to octet rule.