Question

Question 4.33 Explain the formation of H2 molecule on the basis of valence bond theory.

Class XI Chemical Bonding and Molecular Structure Page 131

Answer 1

Formation of Hydrogen atom
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Let two Hydrogen atoms A and B , we know each contains one electron in its 1s - subshell.
when the distance between two atoms is large then there is no attraction force act between them. as these two atoms approach each other , then attractive force and repulsive force begin to operate.

(i) attractive forces arises between nucleus of A and electron of B and vice - versa .
$e.g., N_A-e_B,N_B-e_A$
(ii) repulsive force arises between nuclei of two atoms A and B .
$e.g., N_A-N_B$
(iii) repulsive force arises between electrons of two atoms A and B .
$e.g., e_A-e_B$
see attachment , for understanding forces, how is acting between them .

repulsive forces tend to push them apart while attractive forces tends to bring close to each other . As they apart to come closer to each other from infinite distance, the energy of system starts decreasing as the force of attraction exceed the force of repulsion. ultimately at certain distance , the net force of attraction balance the force of repulsion and system acquire minimum energy .
At this stage , two atoms of H are said to bonded together to form stable molecule having bond Length 74 pm .

in the formation of H2 molecule , the released energy is called Bond energy or enthalpy .

Answer 2

Answer :

According to Kossel and Lewis, atoms combine together in order to complete their respective octets so as to acquire the stable inert gas configuration. This can occur in two ways; by transfer of one or more electrons from one atom to other or by sharing of electrons between two or more atoms.