Question

Which of the following bonds has the highest bond energy?
(A) C - C
(B) Si - Si
(C) Ge - Ge
(D) Sn - Sn

Answer 1

Hint: Think what happens to atomic and ionic radii as we move down the group. Also, think about the relation between bond-length and bond-strength. As the bond strength increases, bond energy decreases and the bond becomes more stable. Use this relation to get the answer.

Complete answer:
- Let’s have a look at the options given in the question.
We can see that the atoms present in all the four bonds that are, carbon, silicon, germanium and tin are from the same group. All are elements that are a part of the Carbon family.
(A) C – C – We are well aware about the catenation property of carbon which has a whole world of organic chemistry. Carbon has the smallest atomic size amongst all other elements present in its group. Due to small atomic size, the bond formed between two carbon atoms will be shorter. Shorter the bond, more is the bond strength. Therefore, the bond is very stable and has low energy.

(B) Si – Si – Silicon is also known for its property of catenation. It also has a small atomic size compared to Ge and Sn and consists of vacant 3d-orbitals. Therefore, the bond length is small and bond strength is high. Therefore, this bond is stable and has less energy.

(C) Ge – Ge – In Germanium, there are completely filled 3d-orbitals which give rise to shielding effect and therefore, germanium has larger atomic size. Since the atomic radius is more, bond formed is long. As the bond length increases, bond strength decreases. Therefore, as the bond strength is less, bond energy is more.

(D) Sn – Sn – In tin, there are completely filled 3d-orbitals and 4d-orbitals which in turn have higher screening effect and large atomic size. As the atomic size is huge, the bond between two tin atoms will have high bond length and low bond strength. As the bond has low bond strength, it has the highest bond energy.
- Therefore, Sn-Sn bond has the highest bond energy.

Therefore, the correct option is option (D).

Note:
Remember the important correlations. If the bond energy is more, the bond will easily break that means it is having very less bond strength. If the bond length is more, bond energy will be more and bond strength will be less. As the atomic size increases, bond length increases.