Hydrogen and chlorine react together to form hydrogen chloride gas. Explain why hydrogen chloride is a molecule and describe the type of bonding present in it.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Hydrogen chloride (HCl) is a gas at room temperature. It is used in industrial processes and forms when hydrogen gas reacts with chlorine gas. Both hydrogen and chlorine are non-metals.
Model answer (5 marks)
Hydrogen chloride is a molecule because it consists of at least two atoms held together by covalent bonds.
A covalent bond is a shared pair of electrons.
Both hydrogen and chlorine are non‑metals, so a covalent bond forms between them.
Each hydrogen atom has one electron in its outer shell and shares it with one electron from chlorine.
Sharing electrons gives both atoms a full outer electron shell, a stable electron arrangement.
A covalent bond is a shared pair of electrons.
Both hydrogen and chlorine are non‑metals, so a covalent bond forms between them.
Each hydrogen atom has one electron in its outer shell and shares it with one electron from chlorine.
Sharing electrons gives both atoms a full outer electron shell, a stable electron arrangement.
Examiner tips
- Use the word ‘molecule’ and explain the covalent bond. Mention that H and Cl are non‑metals. Show the electron sharing and the resulting stable shells. Keep the answer concise and use correct terminology.
Common mistakes
- Confusing ‘molecule’ with ‘compound’. Saying the bond is ionic. Omitting that both atoms share electrons or that they are non‑metals.
Mark scheme (5 marks)
- Hydrogen chloride is a molecule because it contains at least two atoms held together by covalent bonds
- A covalent bond is a shared pair of electrons
- Both hydrogen and chlorine are non-metals, so a covalent bond forms between them
- Each hydrogen atom has one electron in its outer shell and shares it with one electron from chlorine
- Sharing electrons gives both atoms a full outer electron shell / stable electron arrangement
Key terms in this question
Related
- All OCR A-Level Chemistry B: Salters (H433) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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