A-Level Chemistry May/June 2024 Q1(a)(i): Explain the lack of reactivity of nitrogen gas, N2(g).

1 answer

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  Nitrogen gas (N₂) is very unreactive due to its bonding and molecular structure.

  1. The N₂ molecule features a very strong N≡N triple covalent bond. A large amount of energy (high activation energy) is required to break this bond, which is the first step in most chemical reactions.

  2. The N₂ molecule is non-polar. As it is a diatomic molecule with two identical atoms, there is no difference in electronegativity, and the bonding electrons are shared equally. This lack of a permanent dipole makes it less susceptible to attack by electrophilic or nucleophilic reagents.

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  How the marks are awarded

  • M1 — The first mark is awarded for identifying the strong triple covalent bond in the nitrogen molecule. The model answer explicitly states 'a very strong N≡N triple covalent bond'.
  • M2 — The second mark is awarded for stating that the nitrogen molecule is non-polar. The model answer correctly states 'The N₂ molecule is non-polar'.

  Common mistakes

  • Only mentioning the strong bond but not specifying that it is a triple bond.
  • Confusing the strong covalent bond within the molecule with the weak intermolecular forces between molecules. The weak intermolecular forces explain nitrogen's low boiling point, not its lack of chemical reactivity.
  • Only providing one reason (usually the strong triple bond) and therefore failing to score the second mark for polarity.
  • Giving vague answers like 'nitrogen is stable' or 'it has a full outer shell' without linking this to the specific chemical reasons for its inertness (high bond enthalpy and non-polar nature).

  Examiner tip: For 'explain' questions about a substance's properties, always consider both its bonding (e.g., bond type and strength) and its molecular structure (e.g., polarity).

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