Chemical Bonding And Molecular Structure Question 467
Question: Bond order normally gives idea of stability of a molecular species. All the molecules viz. $ H_2,Li_2 $ and $ B_2 $ have the same bond order yet they are not equally stable. Their stability order is
Options:
A) $ H_2>Li_2>B_2 $
B) $ Li_2>H_2>B_2 $
C) $ Li_2>B_2>H_2 $
D) $ B_2>H_2>Li_2 $
Show Answer
Answer:
Correct Answer: A
Solution:
- The molecular orbital configuration of the given molecules is $ H_2=\sigma {{(1s)}^{2}} $ (no electron anti-bonding) $ Li_2=\sigma {{(1s)}^{2}}\sigma *{{(1s)}^{2}}\sigma {{(2s)}^{2}} $ (two anti-bonding electrons) $ B_2=\sigma {{(1s)}^{2}}\sigma *(1s^{2})\sigma {{(2s)}^{2}}\sigma *{{(2s)}^{2}} $
$ \pi {{(2p_{x})}^{1}}=\pi {{(2p_{y})}^{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 $ H_2>Li_2>B_2 $
