GCSE Chemistry revision

Group 7

The periodic table

AQA 4.1.2.6 Foundation & Higher

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Fluorine is a poisonous yellow gas and is the most reactive halogen.
Chlorine is a poisonous green gas and is less reactive than fluorine.
Bromine is a poisonous, reddish-brown volatile liquid at room temperature.
Iodine is a dark grey solid that can form poisonous purple vapours, but is also used as an antiseptic.

1. Meet the Halogens (Group 7) AQA

Fluorine is a poisonous yellow gas and is the most reactive halogen.
Chlorine is a poisonous green gas and is less reactive than fluorine.
Bromine is a poisonous, reddish-brown volatile liquid at room temperature.
Iodine is a dark grey solid that can form poisonous purple vapours, but is also used as an antiseptic.

All halogens exist as diatomic molecules, meaning they consist of pairs of atoms (e.g. Cl₂), held together by a covalent bond formed by sharing electrons.
Halogens can also form covalent bonds with other non-metals, such as hydrogen or carbon, producing compounds like hydrogen fluoride (HF) or carbon tetrachloride (CCl₄).
These halogen-containing covalent compounds are known as simple molecular structures.

2. Diatomic Molecules & Covalent Bonding AQA

All halogens exist as diatomic molecules, meaning they consist of pairs of atoms (e.g. Cl₂), held together by a covalent bond formed by sharing electrons.
Halogens can also form covalent bonds with other non-metals, such as hydrogen or carbon, producing compounds like hydrogen fluoride (HF) or carbon tetrachloride (CCl₄).
These halogen-containing covalent compounds are known as simple molecular structures.

Melting points and boiling points increase as you go down Group 7.
Reactivity decreases as you go down Group 7.
This decrease in reactivity occurs because the outermost shell gets further from the positive nucleus, weakening the attractive force needed to pull in an extra electron.
Iodine, being lower in the group, is the least reactive halogen because its outer shell electrons are furthest from the nucleus.

3. Trends Down Group 7 AQA

Melting points and boiling points increase as you go down Group 7.
Reactivity decreases as you go down Group 7.
This decrease in reactivity occurs because the outermost shell gets further from the positive nucleus, weakening the attractive force needed to pull in an extra electron.
Iodine, being lower in the group, is the least reactive halogen because its outer shell electrons are furthest from the nucleus.

When a halogen gains one electron, it forms a 1− ion called a halide ion.
The names of halide ions are: fluoride, chloride, bromide, and iodide.
Halogens commonly form ionic compounds with Group 1 alkali metals, for example sodium chloride (NaCl), but can also bond ionically with metals from other groups.

4. Halide Ions & Ionic Bonding AQA

When a halogen gains one electron, it forms a 1− ion called a halide ion.
The names of halide ions are: fluoride, chloride, bromide, and iodide.
Halogens commonly form ionic compounds with Group 1 alkali metals, for example sodium chloride (NaCl), but can also bond ionically with metals from other groups.

A more reactive halogen can displace a less reactive halogen from a solution of its salt, in a reaction called a displacement reaction.
For example, chlorine gas bubbled into potassium bromide solution displaces the bromide ions, forming potassium chloride, because chlorine is more reactive than bromine.
The key rule is that a more reactive halogen will always displace a less reactive one — for instance, fluorine, chlorine, and bromine can all displace iodine.

5. Displacement Reactions AQA

A more reactive halogen can displace a less reactive halogen from a solution of its salt, in a reaction called a displacement reaction.
For example, chlorine gas bubbled into potassium bromide solution displaces the bromide ions, forming potassium chloride, because chlorine is more reactive than bromine.
The key rule is that a more reactive halogen will always displace a less reactive one — for instance, fluorine, chlorine, and bromine can all displace iodine.