Nitrogen and hydrogen react together to form ammonia, NH₃. Explain why ammonia is a molecule and not an ionic compound, and describe the type of bonding present in ammonia.

OCR A-Level Chemistry B: Salters (H433) — 2.1 Atoms, compounds, molecules and equations · Explain · 5 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Ammonia is a gas produced on a large industrial scale and is used in the manufacture of fertilisers. Its formula is NH₃.

Model answer (5 marks)

Ammonia is a molecule because it consists of at least two atoms (N and H) held together by covalent bonds. Both nitrogen and hydrogen are non‑metals, so the atoms share electrons rather than transfer them. In a covalent bond a pair of electrons is shared between the atoms, giving each atom a stable electron configuration. Ionic compounds, by contrast, involve a metal donating electrons to a non‑metal, forming ions that are held together by electrostatic attraction. Since no ions are formed and no electron transfer occurs in NH₃, it is a covalent molecule, not an ionic compound.

Examiner tips

  • State that N and H are non‑metals and that covalent bonds involve sharing of electrons; this shows why NH₃ is a molecule.
  • Explain that ionic compounds require a metal and involve electron transfer; contrast this with NH₃’s bonding.
  • Use the exact terms "covalent bond" and "shared pair of electrons" to match the mark scheme.
  • Keep the answer concise – 5 marks can be earned with 2–3 short sentences.

Common mistakes

  • Confusing covalent with metallic bonding or saying NH₃ is ionic because it contains a metal; nitrogen is not a metal.
  • Failing to mention that both atoms are non‑metals, which is key to covalent bonding.
  • Using vague language such as "bonds together" without specifying covalent or ionic.

Mark scheme (5 marks)

  1. Nitrogen and hydrogen are both non-metals
  2. A molecule is a group of at least two atoms held together by covalent bonds
  3. A covalent bond is a shared pair of electrons
  4. Ionic compounds require a metal and a non-metal / ionic bonding involves transfer of electrons to form ions
  5. Because no ions are formed / no electron transfer occurs, ammonia is a molecule not an ionic compound

Key terms in this question

molecule · ionic compound

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