3.2.3 - the halogens

What is the trend in electronegativity down Group 7 (halogens)?

Electronegativity decreases down the group.

Why does electronegativity decrease down the halogens?

• Atomic radius increases

• More electron shells

• Increased shielding

• Nucleus attracts bonding electrons less strongly

What is the trend in boiling point down Group 7?

Boiling point increases down the group.

Why do boiling points increase down the halogens?

• Molecules get larger with more electrons

• Stronger London dispersion forces between molecules

• More energy needed to separate molecules

What type of structure do halogens have?

Simple molecular structure with weak intermolecular forces.

What is the trend in oxidising ability down Group 7?

Decreases down the group.

Which halogen is the strongest oxidising agent?

Fluorine (F₂).

Which halogen is the weakest oxidising agent?

Iodine (I₂).

What does an oxidising agent do?

Accepts electrons (is reduced).

Why does oxidising ability decrease down Group 7?

• Atoms get larger

• More shielding

• Nucleus attracts incoming electron less strongly

What happens in halogen displacement reactions?

A more reactive halogen displaces a less reactive halide ion from solution.

Give an example of a displacement reaction.

Cl₂ + 2Br⁻ → 2Cl⁻ + Br₂

Which halogens can chlorine displace?

Bromide and iodide ions.

Which halide ion can iodine displace?

None (iodine is least reactive).

What is the trend in reducing ability of halide ions down Group 7?

Increases down the group.

Which halide ion is the strongest reducing agent?

I⁻ (iodide).

Which halide ion is the weakest reducing agent?

F⁻ (fluoride).

What does a reducing agent do?

Donates electrons (is oxidised).

What type of reaction occurs between NaCl and concentrated H₂SO₄?

Acid–base reaction only.

Product when NaCl reacts with concentrated sulfuric acid?

Hydrogen chloride gas (HCl).

What happens when NaBr reacts with concentrated H₂SO₄?

Redox reaction occurs producing Br₂ and SO₂.

What happens when NaI reacts with concentrated H₂SO₄?

Strong redox reactions producing I₂, SO₂, S, and H₂S.

Which reagent is used to test for halide ions?

Acidified silver nitrate (AgNO₃).

What precipitate forms with chloride ions?

White precipitate (AgCl).

What precipitate forms with bromide ions?

Cream precipitate (AgBr).

What precipitate forms with iodide ions?

Yellow precipitate (AgI).

Why is nitric acid added before silver nitrate?

To remove carbonate or hydroxide ions that would also form silver precipitates.

Why is nitric acid used instead of hydrochloric acid?

HCl contains chloride ions, which would give a false positive.

Why is ammonia added after silver nitrate?

To distinguish between the silver halide precipitates.

Which silver halide dissolves in dilute ammonia?

AgCl (silver chloride).

Which silver halide dissolves in concentrated ammonia?

AgBr (silver bromide).

Which silver halide does not dissolve in ammonia?

AgI (silver iodide).