Group 7

trend in melting/boiling point down group

increases

F colour

pale yellow

Cl colour

green/ yellow

Br colour

orange/ brown

I colour

black solid, purple gas

trend in volatility down group

decreases

What is a halogen when it reacts with a metal

Oxidising agent

trend in reactivity down group

decreases

trend in oxidising power down group

decreases

evidence for trend in oxidising power

displacement reactions

what solvent used to determine colour of displaced ion

cyclohexane

F2 w h2 (obs)

explosive reaction, (even in dark)

Halogen w H2

HX

Cl2 w H2 (obs)

explosively in sunlight

Br2 w H2 (reactivity)

slowly (on heating)

I2 w H2 (reactivity)

Forms equilibrium mixture (on heating)

trend in thermal stability down group

decreases

what determines thermal stability

bond length (longer bond = weaker)

test for halide ions

nitric acid, silver nitrate

Cl ppt w dilute ammonia

dissolves

Br ppt w dilute ammonia

insoluble

I ppt w dilute ammonia

insoluble

Cl ppt w conc ammonia

dissolves/ soluble

Br ppt w conc ammonia

dissolves

I ppt w conc ammonia

insoluble

NaCl w H2SO4

NaHSO4, HCl

why doesn’t H2SO4 further oxidise HCl

not strong enough oxidising agent (HCl more thermally stable)

NaBr w H2SO4

NaHSO4, HBr, Br2, SO2, H2O

NaBr w H2SO4 (obs)

red/ brown gas

NaI w H2SO4

NaHSO4, HI, I2, SO2, H2O, H2S, S

NaI w H2SO4 (obs)

yellow solid, bad egg smell, purple gas

How do I and Br act w H2SO4

reducing agents

Cl2 w cold alkali (15)

NaCl, NaClO, H2O

Cl2 w hot alkali (70)

NaCl, NaClO3, H2O

Cl2 w H2O

HCl, HClO

what is sterlising agent

ClO-