Inorganic: Group 17 (F, Cl, Br, I)

Trend of volatility (how easy it evaporates) down the group

→ Volatility decreases down the group

• As radius of element decreases down the group, more electrons get added.

• Down the group, id-id forces get stronger.

• More thermal energy is required to overcome the forces of attraction.

Chemical reactivity down the group

Cl > Br > I

Thermal stability and bond energies of the group

1) HI has the lowest bond energy and is easily decomposed. Purple vapour of I2 vapour observed in heating.

2) HBr decomposes slightly. Slight browning observed on heating

3) HCl does not decompose on heating.

HCl > HBr > HI

431 > 366 > 299

Acid strength down the group

HI > HBr > HCl

• Due to increasing strength of H-X bond

• H3O+ and X- forms more easily with HI

Reaction with H2

1) Cl2 → 2HCL : rapid reaction, exploded in the presence of light

2) Br2 → 2HBr : slow reaction, heat @ 200*C with Pt catalyst

3) I2 → 2HI → no reaction (reversible reaction)

Ease of oxidation down the group

1) HCl → only be oxidised by KMnO4, H2SO4, MnO2

2) HBr → oxidised by H2SO4, H2O2

3) HI → oxidised by atmospheric O2

Hydrides power as reducing agents: HI > HBr > HCl

Reactions with silver nitrate and ammonia

1) Cl- forms white ppt with AgNO3 and a colourless solution in NH3

2) Br- forms cream ppt with AgNO3 and a colourless solution with NH3

3) I- forms yellow ppt with AgNO3 and is completely insoluble in NH3

Reactions with sulfuric acid

1) Cl- forms white fumes of HCl

2) Br- forms white fumes of HBr and brown fumes of Br2

3) I- forms white fumes of HI and purple vapour of I2

Reactions of chlorine and NaOH

1) Cold NaOH → produces sodium chlorate (I)

2) Hot NaOH → produces sodium chlorate (V)