Bond order normally gives idea of stability of a molecular species. All the molecules viz. H2, Li2 and B2 have the same bond order yet they are not equally stable. Their stability order is
(a) H2 > Li2 > B2
(b) Li2 > H2 > B2
(c) Li2 > B2 > H2
(d) B2 > H2 > Li2
Correct answer: (a) H2 > Li2 > B2
Explanation:
The molecular orbital configuration of the given molecules is
H2 = σ(1s)2(no electron anti-bonding)
Li2 = σ(1s)2σ*(1s)2σ(2s)2
(two anti-bonding electrons)
B2 = σ(1s)2σ*(1s)2σ(2s)2σ*(2s)2
π(2px)1 = π(2py)1
(4 anti-bonding electrons)
Though the bond order of all the species are same (B.O = 1) but stability is different. This is due to difference in the presence of no. of anti-bonding electron.
Higher the no. of anti-bonding electron lower is the stability hence the correct order is H2 > Li2 > B2