3.2.3 Group 7(17), the Halogens

What are the physical states and colours of halogens at room temperature?

Fluorine: pale yellow gas

Chlorine: greenish gas

Bromine: red/brown liquid

Iodine: black/dark grey solid

What happens to boiling points as you go down Group 7?

They increase due to stronger van der Waals forces as molecular size and mass increase.

Why does electronegativity decrease down Group 7?

Because atomic radius and shielding increase, so attraction to bonding electrons weakens.

What is the trend in oxidising ability down Group 7?

It decreases.

What is the trend in reducing ability of halide ions?

It increases down the group.

Why can’t fluorine be used in aqueous displacement reactions?

It reacts with water because it is such a strong oxidising agent.

Why don’t F⁻ and Cl⁻ take part in redox reactions?

They don’t have enough reducing ability; only acid-base reactions occur.

What observations are seen when NaBr reacts with sulfuric acid?

Steamy fumes (HBr), brown vapour (Br₂), and sulfur reduced from +6 to +4.

What observations are seen when NaI reacts with sulfuric acid?

Steamy fumes (HI), black solid (I₂), rotten egg smell (H₂S), and yellow sulfur may form.

What precipitates form when halide ions react with AgNO₃?

AgCl: white; AgBr: cream; AgI: pale yellow; AgF: no precipitate (soluble)

Why is nitric acid added before testing with silver nitrate?

To remove CO₃²⁻ and OH⁻ impurities that would interfere with the test.

How do the silver halide precipitates behave with ammonia?

AgCl dissolves in dilute ammonia; AgBr dissolves in concentrated ammonia; AgI is insoluble in ammonia

What happens when chlorine reacts with water?

Disproportionation: Cl₂ + H₂O ⇌ HCl + HClO (HClO kills bacteria)

What happens when chlorine reacts with water in sunlight?

HClO doesn't form → chlorine must be added frequently to swimming pools.

What is the reaction between chlorine and cold dilute NaOH?

Cl₂ + 2NaOH → NaCl + NaClO + H₂O (Disproportionation forming bleach)