2.3: Group 7, the Halogens

What is the trend in electronegativity going down group 7?

• Decreases going down the group

• Atomic radius increases and sheilding increases

• Electrostatic attraction decreases so it becomes harder to attract an electron

What is the trend in boiling point going down group 7?

• Increases going down the grouo

• Group 7 are simple molecules with only Van der Waals forces

• Atomic radius increases, so more VDW

• More energy requires to overcome these forces

What is the trend in oxidising ability going down group 7?

Decreases as electronegativity decreases

What is the trend in reducing ability going down group 7?

• Increases going down the group

• Atomic radius and shielding increase

• Weaker electrostatic attraction

• So electrons are released more easily

How do solid sodium halides react with concentrated H₂SO₄ and what is the equation?

X^-(aq) + H₂SO₄(l) → HCl(g) + HSO₄ ^- (aq)

• Chlorine: white gas

• Bromine

What precautions are needed to be taken when reacting solid sodium halides with concentrated H₂SO₄?

Toxic gases produced so experiment must be carried out in a fume cupboard

How are halide ions tested for and what are the results?

• Add nitric acid and then silver nitrate

• Cl- = white ppt

• Br- = cream ppt

• I- = yellow ppt

Why is silver nitrate solution used to identify halide ions?

Ag- ions react with halide ions to form a precipitate with a distinct colour

Why is the silver nitrate solution acidified when identifying halide ions?

To prevent interference from other ions that could also form precipitates with silver ions

Why is ammonia solution added when identifying halide ions, and what are the results of adding NH₃?

Helps distinguish ions as colours are hard to tell apart

• Cl: dissolves in both dilute and conc NH₃

• Br: dissolves in only conc NH₃

• I: dissolves in neither dilute or conc NH₃

What are the equations of halogens reacting with concentrated H₂SO₄?

• H₂SO₄ (l) + NaCl(s) → HCl (g) + NaHSO₄

• H₂SO₄ (l) + NaBr(s) → HBr(g) + NaHSO₄

• H₂SO₄ (l) + NaI(s) → HI (g) + NaHSO₄

What is the reaction of chlorine and water?

Cl₂(aq) + H₂O(l) → HCl(aq) +HClO(g)

What is chlorine used for?

Sterilising agent

What is the reaction of chlorine and water in sunlight?

2Cl₂(aq) + H₂O(l) → 4HCl(aq) +O₂(g)

What is the reaction of chlorine with sodium hydroxide?

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

What is the product of the reaction of chlorine with sodium hydroxide used for?

bleach as a disinfectant