Group 7: The Halogens

Fluorine colour

Pale yellow

Chlorine colour

Green

Bromine colour

Brown

Iodine colour

Dark grey

Astatine colour

Black

Fluorine state at room temperature

Gas

Chlorine state at room temperature

Gas

Bromine state at room temperature

Liquid

Iodine state at room temperature

Crystals

Astatine state at room temperature

Solid

What is the trend in melting and boiling point as you go down group 7?

The points increase

What is the trend in atomic radius as you go down group 7?

Increase

What is the trend in electronegativity as you go down group 7?

Decrease

Using a solubility in water versus hydrocarbon test, how can you tell which solvent the halogens are more soluble in?

They are more soluble in the hydrocarbon as there is a more intense colour.

Why are halogens more soluble in hydrocarbon than in water?

In a hydrocarbon, the VdW forces are easier to break however the hydrogen bonding in water is stronger.

What are the halogen displacement reactions?

Chlorine displaces bromine and iodine

Bromine displaces iodine but not chlorine

Iodine doesn’t displace any halogen

Why can chlorine and bromine displace halogens?

They are more reactive and stronger oxidising agents.

Which halogen in a displacement reaction is oxidised?

The ion that is displaced loses an electron

Which halogen in a displacement reaction is reduced?

The atom that displaces gains an electron

Equation for reaction between chlorine and water

Cl₂ + H₂O → HCl + HCLO

Products of chlorine and water reaction

Hydrochloric acid, Chloric (I) acid

Oxidation number of chlorine at the start of the reaction with water

0

Oxidation number of chlorine in HCl

-1

Oxidation number of chlorine in HClO

+1

How can you tell the reaction between chlorine and water is a disproportionation reaction?

Chlorine’s oxidation number has both increased (chloric acid) and decreased (hydrochloric acid)

Reaction between chlorine and water in the presence of sunlight

2Cl₂ + 2H₂O → 4HCl + O₂

Why is the reaction between chlorine and water different in the presence of sunlight?

Chlorine oxidises the water so is rapidly lost from the pool water .

What is an alternative to direct chlorination of swimming pools?

Adding solid sodium chlorate (NaClO) which dissolves in water to form chloric acid.

Equation for reaction between water and sodium chlorate

NaClO + H₂O <-> Na⁺ + OH^- + HClO

Why is acidity of swimming pools necessary?

To prevent the equilibrium in the equation from moving to the left which leads to HClO being removed as ClO^- ions.

Why is the acidity of swimming pools monitored?

So the water never gets acidic enough to corrode metal or affect swimmers.

Why is chlorine added to water for drinking purposes?

It kills pathogens responsible for water-borne diseases (cholera).

Kills microrganisms

Chloric (I) acid is an oxidising agent that kills bacteria by oxidation