Halogens are the Group 7 non-metal elements that exist as diatomic molecules at room temperature and decrease in reactivity and oxidising power going down the group.

The .......... of halogens increases going down Group 7, while their .......... decreases.

The boiling point of halogens increases going down Group 7, while their volatility decreases.

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

Going down Group 7, the molecules have more electrons , so the London dispersion forces between molecules are stronger. More energy is needed to separate the molecules, raising the boiling point.

True or False? Fluorine is the most volatile halogen.

True. Fluorine has the lowest boiling point of all the halogens. Its small molecules have the weakest London dispersion forces , so it evaporates most easily.

Define electronegativity .

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

Why does electronegativity decrease going down Group 7?

Going down Group 7, atomic radius increases and there are more shielding electrons between the nucleus and the outer shell. An incoming electron experiences less attraction from the nucleus, reducing the atom's ability to attract electrons.

The .......... power of halogens decreases going down Group 7 because larger atoms find it harder to attract .......... .

The oxidising power of halogens decreases going down Group 7 because larger atoms find it harder to attract electrons .

Why does the reactivity of halogens decrease going down Group 7?

Going down Group 7, atomic radius increases and shielding increases, so halogens find it harder to gain an electron to form a 1- ion . Their ability to act as oxidising agents therefore decreases.

True or False? Halogens act as oxidising agents when they react.

True. Halogens gain an electron to form a 1- ion , so their oxidation number decreases from 0 to -1. Gaining electrons is reduction , so halogens act as oxidising agents.

Predict the colour and boiling point of astatine (At) compared to iodine, giving a reason for each.

Colour: astatine would appear darker than iodine (which is grey/black as a solid), because colour gets darker going down Group 7 Boiling point: astatine would have a higher boiling point than iodine, because larger At 2 molecules have more electrons, so London dispersion forces between molecules are stronger and more energy is needed to separate them

What is a halogen displacement reaction ?

A halogen displacement reaction is a redox reaction in which a more reactive halogen displaces a less reactive halide ion from its aqueous solution.

The order of halogen reactivity as oxidising agents is: .......... > Br 2 > .......... .

The order of halogen reactivity as oxidising agents is: Cl 2 > Br 2 > I 2 .

What is observed when Cl 2 (aq) is added to a solution of bromide ions?

The colourless solution turns orange as Br 2 is produced. Cl 2 is more reactive, so it displaces Br - , reducing from oxidation state 0 to -1 while Br - is oxidised from -1 to 0.

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

False. Bromine is less reactive than chlorine, so it cannot displace chloride ions . Only a more reactive halogen can displace a less reactive halide ion .

What colour does iodine produce in an organic solvent such as cyclohexane?

Iodine produces a purple or violet colour in an organic solvent. This distinctive colour confirms that I 2 has been formed in a displacement reaction.

Cl 2 (aq) + 2I - (aq) → 2 .......... (aq) + .......... (aq)

Cl 2 (aq) + 2I - (aq) → 2 Cl - (aq) + I 2 (aq)

Why is an organic solvent such as cyclohexane added when observing halogen displacement reactions?

The colour change in aqueous solution can be ambiguous , for example distinguishing orange bromine from brown iodine. The organic solvent forms a separate layer that concentrates the halogen, making the colour more distinct and easier to identify.

True or False? In a halogen displacement reaction, the more reactive halogen is oxidised.

False. The more reactive halogen is reduced — it gains electrons and its oxidation state decreases from 0 to -1. It is the less reactive halide ion that is oxidised.

What is observed when Br 2 (aq) is added to potassium iodide solution and cyclohexane is then added?

The aqueous layer turns brown as I 2 is produced. The organic layer turns purple/violet , confirming that iodine has been formed. Bromine is more reactive than iodine, so it displaces I - from solution.

Define disproportionation reaction .

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

What products form when Cl 2 reacts with cold dilute alkali (approximately 15 °C)?

Cl 2 is disproportionated : it is reduced to Cl - (oxidation state 0 to -1) and oxidised to chlorate(I) ions, ClO - (oxidation state 0 to +1). The products are NaCl and NaClO in sodium hydroxide solution.

True or False? When halogens react with metals, the halogens act as oxidising agents.

True. In reactions with metals, the metal is oxidised (loses electrons) and the halogen is reduced (gains electrons). The halogen therefore acts as an oxidising agent .

Cl 2 (g) + 2Fe 2+ (aq) → 2 .......... (aq) + 2 .......... (aq)

Cl 2 (g) + 2Fe 2+ (aq) → 2 Cl - (aq) + 2 Fe 3+ (aq)

What products form when Cl 2 reacts with hot dilute alkali (approximately 70 °C)?

The products are NaCl and NaClO 3 (sodium chlorate(V)). The chlorate(I) ion formed initially undergoes a further disproportionation reaction to give the more thermally stable chlorate(V) ion, ClO 3 - .

Why do different products form when Cl 2 reacts with cold alkali compared to hot alkali?

In cold alkali, ClO - (chlorate(I)) is stable and accumulates as a product. In hot alkali, ClO - is thermally unstable and undergoes a further disproportionation to form the more stable ClO 3 - (chlorate(V)) and Cl - .

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, Fe 3+ ions can oxidise iodide ions to I 2 , so the reaction goes in the reverse direction.

What is the role of chlorine in treating drinking water?

Chlorine undergoes disproportionation in water to form chloric(I) acid, HClO, and HCl. HClO acts as a sterilising agent , killing bacteria and making the water safe to drink.

2Na (s) + Cl 2 (g) → .......... (s)

2Na (s) + Cl 2 (g) → NaCl (s)

What is the silver nitrate test ?

The silver nitrate test is a method for identifying halide ions in which silver nitrate solution is added to an acidified unknown solution, forming a coloured precipitate of the silver halide (AgX).

Adding AgNO 3 (aq) to Cl - gives a .......... precipitate; to Br - gives a .......... precipitate; to I - gives a pale yellow precipitate.

Adding AgNO 3 (aq) to Cl - gives a white precipitate; to Br - gives a cream precipitate; to I - gives a pale yellow precipitate.

How is ammonia solution used to distinguish between AgCl, AgBr and AgI precipitates?

AgCl (white) dissolves in dilute ammonia. AgBr (cream) is insoluble in dilute ammonia but dissolves in concentrated ammonia. AgI (pale yellow) is insoluble in both dilute and concentrated ammonia.

True or False? Silver chloride precipitate dissolves when dilute ammonia is added.

True. AgCl (white) is the only silver halide precipitate that dissolves in dilute ammonia . AgBr and AgI require concentrated ammonia or are completely insoluble.

Why does reducing power increase going down Group 7 (Cl - to I - )?

Going down Group 7, atomic radius increases and there are more shielding electrons. The outer electrons are held less strongly, so larger halide ions lose electrons more easily, giving them greater reducing power .

When NaBr reacts with concentrated H 2 SO 4 , the HBr produced is further oxidised to .......... gas and .......... gas is also produced as H 2 SO 4 is reduced.

When NaBr reacts with concentrated H 2 SO 4 , the HBr produced is further oxidised to Br 2 gas and SO 2 gas is also produced as H 2 SO 4 is reduced.

What additional products are observed when NaI reacts with concentrated H 2 SO 4 that are not seen with NaBr?

With NaI, the H 2 SO 4 is reduced further to give sulfur (yellow solid) and hydrogen sulfide , H 2 S (bad egg smell), in addition to SO 2 and I 2 . This is because I - is a stronger reducing agent than Br - .

True or False? Concentrated sulfuric acid oxidises HCl to Cl 2 gas.

False. Concentrated H 2 SO 4 does not further oxidise HCl. Only HBr and HI are oxidised by concentrated sulfuric acid, because Br - and I - are stronger reducing agents than Cl - .

What is the order of reducing ability of the halide ions?

The order of reducing ability is: Cl - < Br - < I - . Reducing power increases down Group 7 as atomic radius increases and electrons are lost more easily.

What gas is produced when hydrogen iodide reduces sulfur dioxide?

HI reduces SO 2 to produce hydrogen sulfide , H 2 S, which has a strong bad egg smell. This confirms the maximum reducing power of iodide ions , which is not seen with Cl - or Br - .

A LevelChemistryEdexcelFlashcards2. Inorganic ChemistryGroup 7

Group 7 (Edexcel A Level Chemistry): Flashcards

Exam code: 9CHO

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What are halogens?

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Cards in this collection (38)

What are halogens?
Halogens are the Group 7 non-metal elements that exist as diatomic molecules at room temperature and decrease in reactivity and oxidising power going down the group.
The .......... of halogens increases going down Group 7, while their .......... decreases.
The boiling point of halogens increases going down Group 7, while their volatility decreases.
Why do the boiling points of halogens increase going down Group 7?
Going down Group 7, the molecules have more electrons, so the London dispersion forces between molecules are stronger. More energy is needed to separate the molecules, raising the boiling point.
True or False?
Fluorine is the most volatile halogen.
True.
Fluorine has the lowest boiling point of all the halogens. Its small molecules have the weakest London dispersion forces, so it evaporates most easily.
Define electronegativity.
Electronegativity is the ability of an atom to attract electrons towards itself in a covalent bond.
Why does electronegativity decrease going down Group 7?
Going down Group 7, atomic radius increases and there are more shielding electrons between the nucleus and the outer shell. An incoming electron experiences less attraction from the nucleus, reducing the atom's ability to attract electrons.
The .......... power of halogens decreases going down Group 7 because larger atoms find it harder to attract ...........
The oxidising power of halogens decreases going down Group 7 because larger atoms find it harder to attract electrons.
Why does the reactivity of halogens decrease going down Group 7?
Going down Group 7, atomic radius increases and shielding increases, so halogens find it harder to gain an electron to form a 1- ion. Their ability to act as oxidising agents therefore decreases.
True or False?
Halogens act as oxidising agents when they react.
True.
Halogens gain an electron to form a 1- ion, so their oxidation number decreases from 0 to -1. Gaining electrons is reduction, so halogens act as oxidising agents.
Predict the colour and boiling point of astatine (At) compared to iodine, giving a reason for each.
- Colour: astatine would appear darker than iodine (which is grey/black as a solid), because colour gets darker going down Group 7
- Boiling point: astatine would have a higher boiling point than iodine, because larger At₂ molecules have more electrons, so London dispersion forces between molecules are stronger and more energy is needed to separate them
What is a halogen displacement reaction?
A halogen displacement reaction is a redox reaction in which a more reactive halogen displaces a less reactive halide ion from its aqueous solution.
The order of halogen reactivity as oxidising agents is: .......... > Br₂ > .......... .
The order of halogen reactivity as oxidising agents is: Cl₂ > Br₂ > I₂.
What is observed when Cl₂ (aq) is added to a solution of bromide ions?
The colourless solution turns orange as Br₂ is produced. Cl₂ is more reactive, so it displaces Br^-, reducing from oxidation state 0 to -1 while Br^- is oxidised from -1 to 0.
True or False?
Bromine can displace chloride ions from an aqueous solution.
False.
Bromine is less reactive than chlorine, so it cannot displace chloride ions. Only a more reactive halogen can displace a less reactive halide ion.
What colour does iodine produce in an organic solvent such as cyclohexane?
Iodine produces a purple or violet colour in an organic solvent. This distinctive colour confirms that I₂ has been formed in a displacement reaction.
Cl₂ (aq) + 2I^- (aq) → 2.......... (aq) + .......... (aq)
Cl₂ (aq) + 2I^- (aq) → 2Cl^- (aq) + I₂ (aq)
Why is an organic solvent such as cyclohexane added when observing halogen displacement reactions?
The colour change in aqueous solution can be ambiguous, for example distinguishing orange bromine from brown iodine. The organic solvent forms a separate layer that concentrates the halogen, making the colour more distinct and easier to identify.
True or False?
In a halogen displacement reaction, the more reactive halogen is oxidised.
False.
The more reactive halogen is reduced — it gains electrons and its oxidation state decreases from 0 to -1. It is the less reactive halide ion that is oxidised.
What is observed when Br₂ (aq) is added to potassium iodide solution and cyclohexane is then added?
The aqueous layer turns brown as I₂ is produced. The organic layer turns purple/violet, confirming that iodine has been formed. Bromine is more reactive than iodine, so it displaces I^- from solution.
Define disproportionation reaction.
A disproportionation reaction is a reaction in which the same species is simultaneously both oxidised and reduced.
What products form when Cl₂ reacts with cold dilute alkali (approximately 15 °C)?
Cl₂ is disproportionated: it is reduced to Cl^- (oxidation state 0 to -1) and oxidised to chlorate(I) ions, ClO^- (oxidation state 0 to +1). The products are NaCl and NaClO in sodium hydroxide solution.
True or False?
When halogens react with metals, the halogens act as oxidising agents.
True.
In reactions with metals, the metal is oxidised (loses electrons) and the halogen is reduced (gains electrons). The halogen therefore acts as an oxidising agent.
Cl₂ (g) + 2Fe²⁺ (aq) → 2.......... (aq) + 2.......... (aq)
Cl₂ (g) + 2Fe²⁺ (aq) → 2Cl^- (aq) + 2Fe³⁺ (aq)
What products form when Cl₂ reacts with hot dilute alkali (approximately 70 °C)?
The products are NaCl and NaClO₃ (sodium chlorate(V)). The chlorate(I) ion formed initially undergoes a further disproportionation reaction to give the more thermally stable chlorate(V) ion, ClO₃^-.
Why do different products form when Cl₂ reacts with cold alkali compared to hot alkali?
In cold alkali, ClO^- (chlorate(I)) is stable and accumulates as a product. In hot alkali, ClO^- is thermally unstable and undergoes a further disproportionation to form the more stable ClO₃^- (chlorate(V)) and Cl^-.
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, Fe³⁺ ions can oxidise iodide ions to I₂, so the reaction goes in the reverse direction.
What is the role of chlorine in treating drinking water?
Chlorine undergoes disproportionation in water to form chloric(I) acid, HClO, and HCl. HClO acts as a sterilising agent, killing bacteria and making the water safe to drink.
2Na (s) + Cl₂ (g) → .......... (s)
2Na (s) + Cl₂ (g) → NaCl (s)
What is the silver nitrate test?
The silver nitrate test is a method for identifying halide ions in which silver nitrate solution is added to an acidified unknown solution, forming a coloured precipitate of the silver halide (AgX).
Adding AgNO₃ (aq) to Cl^- gives a .......... precipitate; to Br^- gives a .......... precipitate; to I^- gives a pale yellow precipitate.
Adding AgNO₃ (aq) to Cl^- gives a white precipitate; to Br^- gives a cream precipitate; to I^- gives a pale yellow precipitate.
How is ammonia solution used to distinguish between AgCl, AgBr and AgI precipitates?
AgCl (white) dissolves in dilute ammonia. AgBr (cream) is insoluble in dilute ammonia but dissolves in concentrated ammonia. AgI (pale yellow) is insoluble in both dilute and concentrated ammonia.
True or False?
Silver chloride precipitate dissolves when dilute ammonia is added.
True.
AgCl (white) is the only silver halide precipitate that dissolves in dilute ammonia. AgBr and AgI require concentrated ammonia or are completely insoluble.
Why does reducing power increase going down Group 7 (Cl^- to I^-)?
Going down Group 7, atomic radius increases and there are more shielding electrons. The outer electrons are held less strongly, so larger halide ions lose electrons more easily, giving them greater reducing power.
When NaBr reacts with concentrated H₂SO₄, the HBr produced is further oxidised to .......... gas and .......... gas is also produced as H₂SO₄ is reduced.
When NaBr reacts with concentrated H₂SO₄, the HBr produced is further oxidised to Br₂ gas and SO₂ gas is also produced as H₂SO₄ is reduced.
What additional products are observed when NaI reacts with concentrated H₂SO₄ that are not seen with NaBr?
With NaI, the H₂SO₄ is reduced further to give sulfur (yellow solid) and hydrogen sulfide, H₂S (bad egg smell), in addition to SO₂ and I₂. This is because I^- is a stronger reducing agent than Br^-.
True or False?
Concentrated sulfuric acid oxidises HCl to Cl₂ gas.
False.
Concentrated H₂SO₄ does not further oxidise HCl. Only HBr and HI are oxidised by concentrated sulfuric acid, because Br^- and I^- are stronger reducing agents than Cl^-.
What is the order of reducing ability of the halide ions?
The order of reducing ability is: Cl^- < Br^- < I^-. Reducing power increases down Group 7 as atomic radius increases and electrons are lost more easily.
What gas is produced when hydrogen iodide reduces sulfur dioxide?
HI reduces SO₂ to produce hydrogen sulfide, H₂S, which has a strong bad egg smell. This confirms the maximum reducing power of iodide ions, which is not seen with Cl^- or Br^-.

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