Question

The correct order of bond enthalpy \(\left( kJ mol ^{-1}\right)\) is :

• A. \(C - C > Si - Si > Ge - Ge > Sn - Sn\)
• B. \(C - C > Si - Si > Sn - Sn > Ge - Ge\)
• C. \(Si - Si > C - C > Ge - Ge > Sn - Sn\)
• D. \(Si - Si > C - C > Sn - Sn > Ge - Ge\)

Hint:

Remember that bond enthalpy generally decreases down a group due to the increase in atomic size and bond length.

Answer 1

The Correct Option is A

 To determine the correct order of bond enthalpy for the given bonds, we need to understand the concept of bond enthalpy. Bond enthalpy is the energy required to break one mole of a bond in a molecule in the gaseous state.

The bond enthalpies of single bonds involving elements from the carbon group, like C-C, Si-Si, Ge-Ge, and Sn-Sn, are influenced by factors such as bond length, bond order, and atomic size. In general, as the atomic size increases down a group, the bond length increases, leading to weaker bonds and thus lower bond enthalpies.

Let's analyze each option:

1. \(C - C > Si - Si > Ge - Ge > Sn - Sn\): This option indicates that carbon, being the smallest atom among C, Si, Ge, and Sn, forms the strongest bond due to shorter bond length, followed by silicon, germanium, and tin, consistent with increasing atomic size and decreasing bond enthalpy.
2. \(C - C > Si - Si > Sn - Sn > Ge - Ge\): This option places the Sn-Sn bond before Ge-Ge, which is inaccurate because as you move down the group, the bond strength generally decreases consistently.
3. \(Si - Si > C - C > Ge - Ge > Sn - Sn\): This option incorrectly suggests that the Si-Si bond is stronger than the C-C bond, which is not the case because of the shorter bond length and stronger nature of C-C bonds.
4. \(Si - Si > C - C > Sn - Sn > Ge - Ge\): Again, similar to option 3, this option inaccurately places Si-Si above C-C and does not follow the logical decrease down the group.

The correct answer is option 1: \(C - C > Si - Si > Ge - Ge > Sn - Sn\), as it accurately reflects the decreasing bond enthalpy with increasing atomic size down the group.