CAIE A-Level Chemistry AS 11.1.2 Trend in the Bond Strength of the Halogen Questions

Practise describing X–X bond-strength data and explaining differences through atomic size, bond length and orbital overlap.

Exam points

read or compare X–X bond energies directly rather than using intermolecular-force trends
explain a weaker Br–Br than Cl–Cl bond using larger atoms, longer bond length and poorer orbital overlap
separate covalent X–X bond strength from the London forces acting between halogen molecules

[Maximum number: 2]

The Group 17 elements are oxidising agents.

$\mathrm{Cl}_{2}$ and $\mathrm{Br}_{2}$ can each react with $\mathrm{NH}_{3}$ to give $\mathrm{N}_{2}$ and a hydrogen halide, HX .

3 \mathrm{X}_{2}+2 \mathrm{NH}_{3} \rightarrow \mathrm{~N}_{2}+6 \mathrm{HX}

X = Cl or Br

The relative bond strengths of X-X and H-X determine the difference in enthalpy change of the two reactions.

Describe and explain the difference in the X-X bond strengths of $\mathrm{Cl}_{2}$ and $\mathrm{Br}_{2}$ .

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