Methane is a simple molecular substance. Nitrogen gas also exists as a simple molecule. Explain why methane and nitrogen both have low boiling points, and explain why methane and nitrogen are examples of different types of substance (one is a compound and one is an element).
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Methane has the molecular formula CH₄. Nitrogen gas exists as N₂ molecules. Both substances are gases at room temperature and have low boiling points.
Model answer (5 marks)
Both methane and nitrogen have weak intermolecular forces between their molecules. Only a small amount of energy is needed to overcome these forces, so the boiling point is low. Nitrogen (N₂) is an element because it contains only one type of atom. Methane is a compound because it contains two or more different types of atom (carbon and hydrogen) chemically bonded together. The atoms in methane are held together by covalent bonds (shared pairs of electrons between non‑metals).
Examiner tips
- Use the word ‘weak’ to describe the forces, e.g. London dispersion. Mention that both are non‑polar molecules. State clearly that N₂ is an element and CH₄ a compound. Show the covalent bond explanation for CH₄. Keep the answer concise and use exam‑specific terminology.
Common mistakes
- Confusing ‘molecule’ with ‘compound’.
- Forgetting to explain that CH₄ is a compound because it has two different elements.
- Using vague terms like ‘strong’ or ‘weak’ without specifying London dispersion.
Mark scheme (5 marks)
- Both methane and nitrogen have weak intermolecular forces between their molecules
- Only a small amount of energy is needed to overcome these intermolecular forces, so the boiling point is low
- Nitrogen (N₂) is an element because it contains only one type of atom
- Methane is a compound because it contains two or more different types of atom (carbon and hydrogen) chemically bonded together
- The atoms in methane are held together by covalent bonds (shared pairs of electrons between non-metals)
Key terms in this question
Related
- All OCR A-Level Chemistry A (H432) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
More Atoms, compounds, molecules and equations questions
- Sodium chloride is an ionic compound. Explain why sodium chloride has a high mel…
- Water is a molecule made up of hydrogen and oxygen atoms. Explain why water is a…
- Carbon dioxide is a simple molecular compound. Explain why carbon dioxide is des…
- Iron is an element. Steel is an alloy made mostly from iron, with small amounts …