The Halogens

Outer shell electronic configuration of a halogen

s2p5

Halogens exist as …

Diatomic molecules

Fluorine at RTP

Pale yellow gas

Chlorine at RTP

Pale green gas

Bromine at RTP

Red-brown liquid

Iodine at RTP

Shiny grey-black solid

Trend in boiling points down the group

• More electrons

• Stronger London forces

• More energy required to break London forces

• Boiling points increase down the group

Trend in reactivity in forming -1 ions down the group

• Atomic radius increases

• Increasing number of shells, so shielding increases

• Less nuclear attraction to capture electron from other species

• Reactivity decreases

Chlorine in aqueous and organic solution

• Pale green in aqueous solution

• Pale green in organic solution

Bromine in aqueous and organic solution

• Orange in aqueous solution

• Orange in organic solution

Iodine in aqueous and organic solution

• Brown in aqueous solution

• Violet in organic solution

Cl- ions reacting with Bromine

No reaction

Cl- ions reacting with Iodine

No reaction

Br- ions reacting with Iodine

No reaction

Br- ions reacting with Chlorine

Orange colour from Bromine formation

Ionic equation for the displacement reaction between Cl2 and Br-

Cl2 (aq) + 2Br- (aq) → 2Cl- (aq) + Br2 (aq)

I- ions reacting with Chlorine

Violet colour forming from Iodine formation

Ionic equation for the displacement reaction between Cl2 and I-

Cl2 (aq) + 2I- (aq) → 2Cl- (aq) + I2 (aq)

I- ions reacting with Bromine

Violet colour forming from Iodine formation

Ionic equation for the displacement reaction between Br2 and I-

Br2 (aq) + 2I- (aq) → 2Br- (aq) + I2 (aq)

Disproportionation

Oxidation and reduction of the same element

Equation of the reaction between Chlorine and water

Cl2 (aq) + H2O (l) → HClO (aq) + HCl (aq)

Oxidation states of Chlorine in the reaction between Chlorine and water

• Reduced from 0 in Cl2 to -1 in HCl

• Oxidised from 0 in Cl2 to +1 in HClO

Equation of the reaction between Chlorine and aqueous NaOH

Cl2 (aq) + 2NaOH (aq) → NaClO (aq) + NaCl (aq) + H2O (l)

Oxidation states of Chlorine in the reaction between Chlorine and NaOH

• Reduced from 0 in Cl2 to -1 in NaCl

• Oxidised from 0 in Cl2 to +1 in NaClO

Best oxidising agent

Fluorine

Using chlorine in water treatment - Benefit

Kills bacteria

Using chlorine in water treatment - Risks

• Extremely toxic gas - respiratory irritant in small concs, fatal in large concs

• Reacts with hydrocarbons, forming chlorinated hydrocarbons - suspected of causing cancer

Solubility of Halides in aqueous NH3

• Chlorine and Bromine are soluble

• Iodine is insoluble