Question

Compare the bond properties of diatomic molecules H2+ , H2, Li2+2 and Li2. Basen on what you can infer from their molecular orbital total energy curve as a function of interatomic separation distance.

Answer 1

Solution:

The s-orbitals of the two H or Li atoms merge to form bonding and * antibonding orbitals.  

Thus,

H2 = 1s2

Bond order = 1

H2+ = 1s1

Bond order = 1/2

Li2 = 1s2 *1s2 2s2

Bond order = 1

Li2^2+ = 1s2 *1s2

Bond order = 0

The increase in the number of antibonding electrons decreases the stability. Thus, the stability follow the order:

H2 > Li2 > H2+ > Li2^2+

Increase in bond order coreesponds to decrease in energy.

Hence, H2 has less energy and Li2^2+ has highest energy.