Halogens are the Group 7 elements: fluorine, chlorine, bromine, and iodine. They are non-metals that exist as diatomic molecules at room temperature and become progressively darker in colour going down the group.

What is a halogen displacement reaction ?

A halogen displacement reaction is a reaction in which a more reactive halogen displaces a less reactive halogen from an aqueous solution of its halide salt.

What is a disproportionation reaction ?

A disproportionation reaction is a reaction in which the same species is simultaneously both oxidised and reduced.

Why does the reducing power of halide ions increase going down Group 7?

Going down the group, the halide ions become larger and have more electron shielding . Their outer electrons are held less tightly by the nucleus, so it is easier to lose electrons, making larger halide ions stronger reducing agents .

Volatility is how easily a substance evaporates. A more volatile substance has a lower boiling point.

What colour change is seen when chlorine water is added to potassium bromide solution?

The solution turns yellow-orange as bromine is displaced and formed in solution. If an organic solvent is added, the organic layer also appears yellow-orange .

What type of compound is formed when a halogen reacts with a Group 1 or Group 2 metal?

An ionic compound called a metal halide salt is formed. In these reactions the metal is always oxidised and the halogen acts as the oxidising agent .

What is observed when concentrated sulfuric acid is added to sodium chloride?

Misty fumes of hydrogen chloride (HCl) gas are produced. No further reaction occurs because Cl - is a weak reducing agent and cannot reduce the sulfuric acid further.

Why do the boiling points of the halogens increase going down Group 7?

Going down the group, the halogen molecules have more electrons, so London dispersion forces between molecules become stronger. More energy is needed to overcome these forces, so the boiling point increases.

What colour change is seen when chlorine water is added to potassium iodide solution?

The solution turns brown as iodine is displaced. If an organic solvent such as cyclohexane is added, the organic layer appears purple .

What oxidation state does iron reach when it reacts with chlorine or bromine?

Iron is oxidised from Fe 2+ to Fe 3+ . Both chlorine and bromine are strong enough oxidising agents to bring about this change.

When concentrated sulfuric acid is added to sodium bromide, a .......... gas is first formed, which is then oxidised to give a .......... gas of bromine.

When concentrated sulfuric acid is added to sodium bromide, a hydrogen bromide gas is first formed, which is then oxidised to give a reddish-brown gas of bromine.

The halogens are held together by .......... . These forces get stronger as the number of .......... in the molecule increases going down the group.

The halogens are held together by London dispersion forces . These forces get stronger as the number of electrons in the molecule increases going down the group.

When bromine solution is added to potassium iodide solution, the solution turns .......... . If an organic solvent is added, the organic layer turns .......... as iodine is formed.

When bromine solution is added to potassium iodide solution, the solution turns brown . If an organic solvent is added, the organic layer turns purple as iodine is formed.

True or False? Iodine can oxidise iron(II) ions to iron(III) ions.

False. Iodine is not a strong enough oxidising agent to oxidise Fe 2+ to Fe 3+ . In fact, iron(III) ions oxidise iodide ions to iodine, not the other way around.

What observations are made when concentrated sulfuric acid is added to sodium iodide?

Misty fumes of HI gas are seen. A purple vapour of I 2 and choking SO 2 gas are produced. A yellow solid of sulfur appears. A bad egg smell of H 2 S gas is detected.

What is the trend in electronegativity going down Group 7?

Electronegativity decreases going down the group. Larger atoms have a greater atomic radius and more electron shielding, so the nucleus attracts bonding electrons less strongly.

Why is an organic solvent useful in halogen displacement reactions?

Halogens are more soluble in the organic layer than in the aqueous layer. This makes the colour changes easier to observe, helping to identify which halogen has been produced.

In the reaction of iodide ions with iron(III), iodide is .......... and iron(III) is .......... .

In the reaction of iodide ions with iron(III), iodide is oxidised and iron(III) is reduced .

What colours are the precipitates formed by Cl - , Br - , and I - with silver nitrate?

AgCl is white . AgBr is cream . AgI is pale yellow . The precipitates are formed by adding silver nitrate solution to the unknown halide solution acidified with nitric acid.

Define electronegativity

Electronegativity is the ability of an atom to attract electrons towards itself in a covalent bond.

In the displacement of bromine by chlorine, which species is oxidised and which is reduced?

Bromine is oxidised: Br goes from -1 to 0. Chlorine is reduced: Cl goes from 0 to -1. The reaction is therefore a redox reaction.

What products are formed when chlorine reacts with cold dilute NaOH (around 15°C)?

Chlorine reacts with cold dilute NaOH to form NaCl and NaClO (sodium chlorate(I)). This is a disproportionation reaction: chlorine is reduced to Cl - (ox. no. 0 to −1) and oxidised to ClO - (ox. no. 0 to +1).

Silver chloride dissolves in .......... ammonia. Silver bromide only dissolves in .......... ammonia. Silver iodide is insoluble in both.

Silver chloride dissolves in dilute ammonia. Silver bromide only dissolves in concentrated ammonia. Silver iodide is insoluble in both.

True or False? Fluorine is the most reactive halogen.

True. Fluorine is the smallest halogen with the least electron shielding. Its nucleus attracts incoming electrons most strongly, making it the most powerful oxidising agent and the most reactive halogen.

A more reactive halogen can .......... a less reactive halogen from a solution of its halide ions because more reactive halogens are stronger .......... .

False. A more reactive halogen can displace a less reactive halogen from a solution of its halide ions because more reactive halogens are stronger oxidising agents .

What products are formed when chlorine reacts with hot concentrated NaOH (around 70°C)?

Chlorine reacts with hot NaOH to form NaCl and NaClO 3 (sodium chlorate(V)). Chlorine is oxidised to ClO 3 - (ox. no. 0 to +5) and reduced to Cl - (ox. no. 0 to −1).

True or False? Silver iodide dissolves in concentrated ammonia solution.

False. Silver iodide does not dissolve in either dilute or concentrated ammonia. This distinguishes iodide from chloride and bromide in the silver nitrate test .

Why does the oxidising power of halogens decrease down Group 7?

Going down the group, atomic radius increases and there is more electron shielding . Incoming electrons are attracted less strongly by the nucleus, so each halogen is less able to gain an electron and act as an oxidising agent .

True or False? Bromine can displace chloride ions from potassium chloride solution.

False. Bromine is less reactive than chlorine. Only a more reactive halogen can displace a less reactive one. Bromine can only displace iodide ions, not chloride ions.

The reaction of chlorine with water is a .......... reaction in which chlorine is reduced to HCl and oxidised to .......... acid.

The reaction of chlorine with water is a disproportionation reaction in which chlorine is reduced to HCl and oxidised to chloric(I) acid.

What is produced when a hydrogen halide gas reacts with ammonia gas?

An ammonium halide salt is formed as a solid. For example, HCl (g) + NH 3 (g) → NH 4 Cl (s).

Going down Group 7, the reaction of the halogens with hydrogen gas becomes less .......... .

Going down Group 7, the reaction of the halogens with hydrogen gas becomes less vigorous .

Write the ionic equation for the displacement of iodide ions by bromine.

Br 2 (aq) + 2I - (aq) → 2Br - (aq) + I 2 (aq) Iodide ions are oxidised (−1 to 0) and bromine is reduced (0 to −1).

How does chlorine make drinking water safe?

Chlorine reacts with water to form chloric(I) acid (HClO), which kills bacteria and acts as a sterilising agent. HClO can also dissociate to form ClO - , which is also a sterilising agent.

Why must reactions of halide ions with concentrated sulfuric acid be carried out in a fume cupboard?

The reactions produce toxic gases such as HCl, HBr, SO 2 , and H 2 S. A fume cupboard prevents these harmful gases from escaping into the laboratory.

Why can silver nitrate not be used to test for fluoride ions?

Silver fluoride (AgF) is soluble in water, so no precipitate forms. This is an exception to the general trend for silver halides, which are insoluble.

International A Level (IAL)ChemistryEdexcelFlashcards2. Energetics, Group Chemistry, Halogenoalkanes & AlcoholsGroup 7

Group 7 (Edexcel International A Level (IAL) Chemistry): Flashcards

Exam code: YCH11

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FrontTrends of the Group 7 Elements
What are halogens?

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Cards in this collection (37)

What are halogens?
Halogens are the Group 7 elements: fluorine, chlorine, bromine, and iodine. They are non-metals that exist as diatomic molecules at room temperature and become progressively darker in colour going down the group.
What is a halogen displacement reaction?
A halogen displacement reaction is a reaction in which a more reactive halogen displaces a less reactive halogen from an aqueous solution of its halide salt.
What is a disproportionation reaction?
A disproportionation reaction is a reaction in which the same species is simultaneously both oxidised and reduced.
Why does the reducing power of halide ions increase going down Group 7?
Going down the group, the halide ions become larger and have more electron shielding. Their outer electrons are held less tightly by the nucleus, so it is easier to lose electrons, making larger halide ions stronger reducing agents.
Define volatility
Volatility is how easily a substance evaporates. A more volatile substance has a lower boiling point.
What colour change is seen when chlorine water is added to potassium bromide solution?
The solution turns yellow-orange as bromine is displaced and formed in solution. If an organic solvent is added, the organic layer also appears yellow-orange.
What type of compound is formed when a halogen reacts with a Group 1 or Group 2 metal?
An ionic compound called a metal halide salt is formed. In these reactions the metal is always oxidised and the halogen acts as the oxidising agent.
What is observed when concentrated sulfuric acid is added to sodium chloride?
Misty fumes of hydrogen chloride (HCl) gas are produced. No further reaction occurs because Cl^- is a weak reducing agent and cannot reduce the sulfuric acid further.
Why do the boiling points of the halogens increase going down Group 7?
Going down the group, the halogen molecules have more electrons, so London dispersion forces between molecules become stronger. More energy is needed to overcome these forces, so the boiling point increases.
What colour change is seen when chlorine water is added to potassium iodide solution?
The solution turns brown as iodine is displaced. If an organic solvent such as cyclohexane is added, the organic layer appears purple.
What oxidation state does iron reach when it reacts with chlorine or bromine?
Iron is oxidised from Fe²⁺ to Fe³⁺. Both chlorine and bromine are strong enough oxidising agents to bring about this change.
When concentrated sulfuric acid is added to sodium bromide, a .......... gas is first formed, which is then oxidised to give a .......... gas of bromine.
When concentrated sulfuric acid is added to sodium bromide, a hydrogen bromide gas is first formed, which is then oxidised to give a reddish-brown gas of bromine.
The halogens are held together by ........... These forces get stronger as the number of .......... in the molecule increases going down the group.
The halogens are held together by London dispersion forces. These forces get stronger as the number of electrons in the molecule increases going down the group.
When bromine solution is added to potassium iodide solution, the solution turns ........... If an organic solvent is added, the organic layer turns .......... as iodine is formed.
When bromine solution is added to potassium iodide solution, the solution turns brown. If an organic solvent is added, the organic layer turns purple as iodine is formed.
True or False?
Iodine can oxidise iron(II) ions to iron(III) ions.
False.
Iodine is not a strong enough oxidising agent to oxidise Fe²⁺ to Fe³⁺. In fact, iron(III) ions oxidise iodide ions to iodine, not the other way around.
What observations are made when concentrated sulfuric acid is added to sodium iodide?
1. Misty fumes of HI gas are seen.
2. A purple vapour of I₂ and choking SO₂ gas are produced.
3. A yellow solid of sulfur appears.
4. A bad egg smell of H₂S gas is detected.
What is the trend in electronegativity going down Group 7?
Electronegativity decreases going down the group. Larger atoms have a greater atomic radius and more electron shielding, so the nucleus attracts bonding electrons less strongly.
Why is an organic solvent useful in halogen displacement reactions?
Halogens are more soluble in the organic layer than in the aqueous layer. This makes the colour changes easier to observe, helping to identify which halogen has been produced.
In the reaction of iodide ions with iron(III), iodide is .......... and iron(III) is ...........
In the reaction of iodide ions with iron(III), iodide is oxidised and iron(III) is reduced.
What colours are the precipitates formed by Cl^-, Br^-, and I^- with silver nitrate?
AgCl is white. AgBr is cream. AgI is pale yellow. The precipitates are formed by adding silver nitrate solution to the unknown halide solution acidified with nitric acid.
Define electronegativity
Electronegativity is the ability of an atom to attract electrons towards itself in a covalent bond.
In the displacement of bromine by chlorine, which species is oxidised and which is reduced?
Bromine is oxidised: Br goes from -1 to 0. Chlorine is reduced: Cl goes from 0 to -1. The reaction is therefore a redox reaction.
What products are formed when chlorine reacts with cold dilute NaOH (around 15°C)?
Chlorine reacts with cold dilute NaOH to form NaCl and NaClO (sodium chlorate(I)). This is a disproportionation reaction: chlorine is reduced to Cl^- (ox. no. 0 to −1) and oxidised to ClO^- (ox. no. 0 to +1).
Silver chloride dissolves in .......... ammonia. Silver bromide only dissolves in .......... ammonia. Silver iodide is insoluble in both.
Silver chloride dissolves in dilute ammonia. Silver bromide only dissolves in concentrated ammonia. Silver iodide is insoluble in both.
True or False?
Fluorine is the most reactive halogen.
True.
Fluorine is the smallest halogen with the least electron shielding. Its nucleus attracts incoming electrons most strongly, making it the most powerful oxidising agent and the most reactive halogen.
A more reactive halogen can .......... a less reactive halogen from a solution of its halide ions because more reactive halogens are stronger ...........
False.
A more reactive halogen can displace a less reactive halogen from a solution of its halide ions because more reactive halogens are stronger oxidising agents.
What products are formed when chlorine reacts with hot concentrated NaOH (around 70°C)?
Chlorine reacts with hot NaOH to form NaCl and NaClO₃ (sodium chlorate(V)). Chlorine is oxidised to ClO₃^- (ox. no. 0 to +5) and reduced to Cl^- (ox. no. 0 to −1).
True or False?
Silver iodide dissolves in concentrated ammonia solution.
False.
Silver iodide does not dissolve in either dilute or concentrated ammonia. This distinguishes iodide from chloride and bromide in the silver nitrate test.
Why does the oxidising power of halogens decrease down Group 7?
Going down the group, atomic radius increases and there is more electron shielding. Incoming electrons are attracted less strongly by the nucleus, so each halogen is less able to gain an electron and act as an oxidising agent.
True or False?
Bromine can displace chloride ions from potassium chloride solution.
False.
Bromine is less reactive than chlorine. Only a more reactive halogen can displace a less reactive one. Bromine can only displace iodide ions, not chloride ions.
The reaction of chlorine with water is a .......... reaction in which chlorine is reduced to HCl and oxidised to .......... acid.
The reaction of chlorine with water is a disproportionation reaction in which chlorine is reduced to HCl and oxidised to chloric(I) acid.
What is produced when a hydrogen halide gas reacts with ammonia gas?
An ammonium halide salt is formed as a solid. For example, HCl (g) + NH₃ (g) → NH₄Cl (s).
Going down Group 7, the reaction of the halogens with hydrogen gas becomes less ...........
Going down Group 7, the reaction of the halogens with hydrogen gas becomes less vigorous.
Write the ionic equation for the displacement of iodide ions by bromine.
Br₂ (aq) + 2I^- (aq) → 2Br^- (aq) + I₂ (aq)
Iodide ions are oxidised (−1 to 0) and bromine is reduced (0 to −1).
How does chlorine make drinking water safe?
Chlorine reacts with water to form chloric(I) acid (HClO), which kills bacteria and acts as a sterilising agent. HClO can also dissociate to form ClO^-, which is also a sterilising agent.
Why must reactions of halide ions with concentrated sulfuric acid be carried out in a fume cupboard?
The reactions produce toxic gases such as HCl, HBr, SO₂, and H₂S. A fume cupboard prevents these harmful gases from escaping into the laboratory.
Why can silver nitrate not be used to test for fluoride ions?
Silver fluoride (AgF) is soluble in water, so no precipitate forms. This is an exception to the general trend for silver halides, which are insoluble.

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