Question

Explain about valence bound theory for the formation of H₂ molecule.

Answer 1

1. Two hydrogen atoms H_a and H_b are separated by infinite distance. At this stage, there is no interaction between these two atoms and the potential energy of this system is arbitrarly taken as zero.

2. As these two atoms approach each other, in addition to electrostatic attractive forces between the nucleus and its own electrons, the following new forces begins to operate

3. The new attractive forces  arise between:

• nucleus of H_a and valence electron of H_b
• nucleus of H_b and the valence electron of H_a

4. The new repulsive forces  arise between:

• the nucleus Of H_a and H_b
• the valence electrons of H_a and H_b

5. The attractive forces tend to bring H_a and H_b together whereas the repulsive forces tends to push them apart.

6. At the initial stage, as the two hydrogen atoms approach each other, the attractive forces are stronger than repulsive forces and the potential energy decreases.

7. A stage is reached where the net attractive forces are exactly balanced by repulsive forces and the potential energy of the system acquires a minimum energy.

8. At this stage, there is a maximum overlap between the atomic orbitals of H_a and H_b and atoms H_a and H_b are now said to be bonded together by a covalent bond.