Question

The average bond energy of C-C bond is \(342 \mathrm{KJ}\) mol \(^{1}\). The bond energy of Si-Si bond is \((1)=342 \mathrm{KJ}\) mol \(^{\prime}\) (2) \(<342 \mathrm{KJ}\) mol 1 (3) \(>342 \mathrm{KJ}\) mol (4) cannot be predicted

Short answer

The bond energy of Si-Si bond is less than 342 KJ/mol.

Step-by-step solution

- Understand Bond Energy

Bond energy refers to the amount of energy needed to break one mole of a particular type of bond in a gaseous molecule. It is usually measured in kilojoules per mole (KJ/mol).

- Compare C-C and Si-Si Bonds

Carbon (C) and Silicon (Si) belong to the same group in the periodic table but have different sizes and bonding properties. Typically, bonds involving larger atoms like Si are weaker due to the increased distance between the bonding electrons and the nucleus, which leads to less effective overlap of orbitals.

- Predict the Bond Energy of Si-Si

Given that Si atoms are larger than C atoms, the Si-Si bond would generally be weaker than the C-C bond. Therefore, the bond energy of the Si-Si bond should be less than that of the C-C bond.

- Choose the Correct Answer

Based on the comparison and reasoning, the bond energy of the Si-Si bond is less than 342 KJ/mol, which aligns with option (2).

Key concepts

C-C bond energy

When we talk about bond energy, we refer to the energy required to break one mole of a bond in a gaseous molecule.
For the carbon-carbon (C-C) bond, this bond energy is typically around 342 KJ/mol.
This value means it takes 342 KJ of energy to separate a mole of carbon atoms from each other when they are in a gaseous state.
The strength of the C-C bond is significant in understanding how different molecules and organic compounds behave.
Since carbon atoms are relatively small, they have strong, stable bonds with each other, which is a reason why carbon is so versatile in forming various compounds.

Si-Si bond energy

Silicon (Si), like carbon, is also found in the same group of the periodic table, known as Group 14.
Despite this, silicon atoms are larger than carbon atoms.
The size difference between Si and C influences their bonding properties.
While the C-C bond energy is 342 KJ/mol, the Si-Si bond energy is typically less than this value.
This is because the larger size of silicon atoms means that the bonding electrons are further away from the nucleus.
As a result, this increased distance reduces the effective overlap of the bonding orbitals, making the Si-Si bond weaker and requiring less energy to break.

Periodic Table Group Trends

Understanding periodic table trends helps explain the properties of elements within the same group.
Elements in the same group usually have similar electronic configurations, which gives them comparable chemical properties.
In Group 14, both carbon and silicon form four bonds in their stable states.
However, as you move down a group in the periodic table, the atomic size increases.
These larger atomic sizes cause the bonding electrons to be farther from the nucleus, generally leading to weaker bonds.
This trend explains why we see stronger bonds in smaller atoms like carbon compared to larger atoms like silicon.

Bond strength and atomic size

The size of an atom significantly impacts bond strength.
Smaller atoms can come closer together, allowing their orbitals to overlap more effectively.
This overlap is key to forming stronger bonds.
For example, carbon atoms are smaller and can create strong C-C bonds.
In contrast, larger silicon atoms have less effective overlap in their Si-Si bonds, making them weaker.
Therefore, bond strength generally decreases as atomic size increases.
This principle helps us understand why the Si-Si bond energy is less than the C-C bond energy.