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CAIE A-Level Chemistry 11.1.2 Halogen X–X Bond Strength

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

Syllabus
2028–2030
Course
Chemistry 9701
Level
AS

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

11.1.2—Trend in the bond strength of the halogen question 1

[Maximum number: 2]

The Group 17 elements are oxidising agents.

Cl2\mathrm{Cl}_{2} and Br2\mathrm{Br}_{2} can each react with NH3\mathrm{NH}_{3} to give N2\mathrm{N}_{2} and a hydrogen halide, HX .

3X2+2NH3→ N2+6HX3 \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 Cl2\mathrm{Cl}_{2} and Br2\mathrm{Br}_{2}.

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