Halogens (Group 7)

Group 7 elements

Highly reactive non-metals, exist as diatomic molecules (X2)

Valence electron configuration

s²p⁵

Ion formed

1- ion (halide)

Atomic radius trend

Increase down the group

Electronegativity trend

Decreases down the group

Melting & boiling points trend

Increase down the group due to van der Waals (London) forces

Reactivity trend

Decreases down the group

Physical state

Fluorine: pale yellow gas

Physical state

Chlorine: pale green gas

Physical state

Bromine: red/brown liquid

Physical state

Iodine: dark grey solid (sublimes purple)

Oxidising power trend

Decreases down the group

Halogen displacement

More reactive halogen displaces less reactive halide ion

Example displacement

Cl2 + 2Br- → Br2 + 2Cl-

Example displacement

Br2 + 2I- → I2 + 2Br-

Iodine displacement

I2 does not displace any halides

Halide ions as reducing agents

Reducing power increases down the group

Disproportionation with water

Cl2 + H2O → HCl + HClO

Disproportionation with cold dilute NaOH

Cl2 + 2NaOH → NaCl + NaClO + H2O

Disproportionation with hot concentrated NaOH

3Cl2 + 6NaOH → 5NaCl + NaClO3 + 3H2O

Reaction with ammonia gas

HX + NH3 → NH4X

Reaction with water

HX + H2O → X- + H3O+

Reaction with Group 1 & 2 metals

Metal + Cl2 → Metal chloride (white precipitate)

Halide test with AgNO3

Cl- forms white precipitate

Halide test with AgNO3

Br- forms cream precipitate

Halide test with AgNO3

I- forms yellow precipitate

Ammonia test

Cl- dissolves in dilute NH3

Ammonia test

Br- dissolves in concentrated NH3

Ammonia test

I- does not dissolve