To arrange the bonds C–Cl, C–Br, C–F, C–I in descending order of average bond energies, we need to understand the concept of bond energy and the factors affecting it.

Bond Energy is the average amount of energy required to break one mole of a particular type of bond in gaseous molecules. It is a measure of bond strength. Higher bond energy means a stronger bond.

For carbon-halogen bonds (C–X, where X is a halogen), bond energy generally decreases as we move down the group in the periodic table (from F to I) due to increasing atomic size. However, there is an exception for C–F bond.

Reasoning:

• Atomic size increases from F to I: F < Cl < Br < I.
• Larger atomic size leads to longer bond length and weaker bond (lower bond energy), so normally bond energy should decrease down the group.
• But fluorine is very small and has high electronegativity, which causes a strong bond due to effective orbital overlap and high polarity. Thus, C–F has the highest bond energy.
• After fluorine, the trend follows: C–Cl > C–Br > C–I.

Therefore, the correct order is: $C–F>C–\mathrm{Cl}>C–\mathrm{Br}>C–I$

Related Topics:

• Bond Length and Bond Energy Relationship
• Periodic Trends in Halogens
• Factors Affecting Bond Strength

Formulae:

Bond energy is inversely related to bond length. Shorter bonds are stronger. Bond length increases with atomic size.