3.1.3 Group 7

Question 1

Why are halogens diatomic?

Answer 1

Element has 7 outer shell electrons (s2p5) so diatomics are formed
Diatomics can form with other halogens e.g. BrI or BrCl

Question 2

What is the trend in boiling points of the halogens?

Answer 2

• boiling point increases down the group
• increased London forces between molecules (more electrons)

Question 3

How are ions formed?

Answer 3

1- ions prevail though expansion of the octet can take the halogens to a higher oxidation state
One electron is gained

Question 4

What is the trend in reactivity?

Answer 4

• reactivity decreases down the group
• atomic radius increases
• shielding increases
• ability to gain e- to become X- is decreased due to decreased attraction from the nucleus

Question 5

How is the trend in reactivity shown?

Answer 5

• displacement reactions
• Cl2(aq) will displace Br-(aq) and I-(aq)
• Br2(aq) will displace I-(aq)
• I2(aq) won’t displace Br-(aq) or Cl-(aq)

Cl2(aq) + 2Br-(aq) -> 2Cl-(aq) + Br2(aq)
Cl2(aq) + 2I-(aq) -> 2Cl-(aq) + I2(aq)
Br2(aq) + 2I(aq) -> 2Br-(aq) + I2(aq)

Question 6

What are the observations for halogens displacement reactions?

Answer 6

Chlorine displaces bromide forming a orange solution
Chlorine displaces iodide forming a brown solution
Bromine displaces iodide forming a brown solution
If organic solvent such as cyclohexane is added then colours are shown more easily as halogens are more soluble in this

Question 7

What are the colour of halogens when aq and in organic solvent?

Answer 7

Aqueous
Chlorine - very pale green solution
Bromine - yellow solution
Iodine - brown solution

Organic solvent
Chlorine - colourless
Bromine - yellow
Iodine - purple

Question 8

What is a disproportionation reaction?

Answer 8

This occurs in a reaction when the same element is oxidised and reduced

Question 9

Reaction of chlorine with water as used in water treatment

Answer 9

Cl2(aq) + H2O(l) -> HOCl(aq) + HCl(aq)
0. +1. -1

Question 10

Reaction of chlorine to form bleach

Answer 10

Cl2(aq) + 2NaOH(aq) -> NaClO(aq) + NaCl(aq) +H2O(l)
COLD DILUTE NaOH

Question 11

Reaction of chlorine with warm NaOH

Answer 11

A more highly oxidised chlorine species can form

3Cl2(aq) + 6NaOH(aq) -> NaClO3(aq) +
0. +5

5NaCl(aq) + 3H2O(l)
-1
Amount of oxidation must equal amount of reduction

Question 12

What are the benefits and hazards of chlorine used in water treatment?

Answer 12

Benefits
- killing bacteria
- preventing disease
Risks
- toxic chlorine gas
- risk from possible formation of chlorinated hydrocarbons