AQA · GCSE · Chemistry
Course version: 8462 · Version from Sept 2018
Students should be able to describe the nature of the compounds formed…
Full specification wording
Group 7: Students should be able to describe the nature of the compounds formed when chlorine, bromine and iodine react with metals and non-metals.
When chlorine, bromine or iodine reacts with a metal, the halogen gains one electron from the metal atom.
Checked against the AQA 8462 specification (opens in a new tab) on .
- Point 3 of 7
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
When chlorine, bromine or iodine reacts with a metal, the halogen gains one electron from the metal atom. The metal loses electrons to form a positive ion and the halogen forms a 1⁻ ion, so the compound is an ionic halide. For example, sodium reacts with chlorine to form sodium chloride, containing Na⁺ and Cl⁻ ions. When a halogen reacts with a non-metal such as hydrogen, electrons are shared rather than transferred, so the compound is covalent. Hydrogen and chlorine form hydrogen chloride, a covalent molecule containing a single covalent bond. The halogen always achieves a full outer shell, either by gaining an electron to form a 1⁻ ion or by sharing an electron pair. The nature of the compound therefore depends on whether the other element is a metal or a non-metal.
What earns the marks
- State that halogens react with metals to form ionic compounds called halides.
- Describe the metal atom losing electrons and the halogen atom gaining one electron to form a 1⁻ ion.
- Give an example such as sodium chloride, formed from Na⁺ and Cl⁻ ions.
- State that halogens react with non-metals such as hydrogen to form covalent compounds.
- Describe the covalent bond in hydrogen chloride as a shared pair of electrons.
- Explain that the halogen completes its outer shell either by gaining one electron or by sharing an electron pair.
Common mistakes and how to put them right
Describing hydrogen chloride as ionic.
Put it right by describing it as a covalent molecule with a shared pair of electrons.
Writing halide ions with baseline numerals and postfix signs.
Put it right by using superscript forms such as Cl⁻ and Br⁻.
Saying the halogen loses an electron when reacting with a metal.
Put it right by stating that the halogen gains one electron.
Confusing the element name chlorine with the ion name chloride.
Put it right by using chloride for the 1⁻ ion in compounds.
Exam tips
- Decide first whether the other element is a metal or a non-metal, because that determines ionic or covalent bonding.
- Name the compound carefully, using the halide ending for ionic compounds, for example sodium bromide.
- Show electron transfer for metals and electron sharing for non-metals in your explanation.
- Use superscript charges for ions and subscript numerals for formulae, for example MgCl₂.
Try the lesson
The start of the Group 7: Students should be able to describe the nature of the compounds formed when chlorine, bromine and iodine react with metals and non-metals. lesson, made from checked teaching notes for this specification point.
Have a go first
What type of compound is formed when chlorine reacts with a metal such as sodium?
Listen
When chlorine, bromine or iodine reacts with a metal, the halogen gains one electron from the metal atom. The metal loses electrons to form a positive ion and the halogen forms a 1⁻ ion, so the compound is an ionic halide. For example, sodium reacts with chlorine to form sodium chloride, containing Na⁺ and Cl⁻ ions. When a halogen reacts with a non-metal such as hydrogen, electrons are shared rather than transferred, so the compound is covalent. Hydrogen and chlorine form hydrogen chloride, a covalent molecule containing a single covalent bond. The halogen always achieves a full outer shell, either by gaining an electron to form a 1⁻ ion or by sharing an electron pair. The nature of the compound therefore depends on whether the other element is a metal or a non-metal. A strong answer earns marks for these points. State that halogens react with metals to form ionic compounds called halides. Describe the metal atom losing electrons and the halogen atom gaining one electron to form a 1⁻ ion. Give an example such as sodium chloride, formed from Na⁺ and Cl⁻ ions. State that halogens react with non-metals such as hydrogen to form covalent compounds. A common slip: Describing hydrogen chloride as ionic. Instead, describing it as a covalent molecule with a shared pair of electrons. Exam tip: Decide first whether the other element is a metal or a non-metal, because that determines ionic or covalent bonding.
See it
Key words
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Reactions of halogens with metals
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Reactions of halogens with non-metals
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Ionic versus covalent bonding
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Formation of halide ions and hydrogen halides
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See every definition
- Reactions of halogens with metals
- The halogen gains one electron from the metal atom, which loses electrons to form a positive ion, so the compound is an ionic halide.
- Reactions of halogens with non-metals
- Electrons are shared rather than transferred, so the compound formed is covalent, as when hydrogen and chlorine form hydrogen chloride.
- Ionic versus covalent bonding
- The nature of the compound depends on whether the other element is a metal or a non-metal, giving electron transfer or electron sharing.
- Formation of halide ions and hydrogen halides
- The halogen achieves a full outer shell either by gaining an electron to form a 1⁻ ion or by sharing an electron pair.
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