Group 7

Question 1

Boiling points

Answer 1

Increase down group, greater induced dipole-dipole forces (more electrons).

Question 2

Change of state equation

Answer 2

X2(x) -> X2(y)

Question 3

Electronegativity

Answer 3

Highest of any group, decreases down group.

Question 4

Factors affecting electronegativity

Answer 4

Nuclear charge: greater n.c. = higher electronegativity.
Distance between nucleus & bonding pair: shorter dist. = higher elect.
Electron shielding: fewer energy levels = higher electronegativity.

Question 5

Reactivity

Answer 5

Reactivity decreases down group. Because of high electronegativity, most halogen reactions involve them acting as oxidising agents. Can be explained w/ electronegativity factors.

Question 6

Reactions with G1 & G2

Answer 6

Most vigorous between bottom G1/2 & top G7. Products= (white) salt. Redox reaction: halogen= oxidising agent.

Question 7

Halogen/Halide displacement reaction.

Answer 7

More reactive halogen displaces less reactive halogen. Occur in aq. solution, so indicated by colour change. Easier to see when organic solvent (eg. cyclohexane) added after reaction and shaken. Hal.= more soluble in o.sol., so hal. dissolves in top o.s. layer.

Question 8

Colours of halogens in organic solvent (cyclohexane).

Answer 8

Chlorine: pale green.
Bromine: orange.
Iodine: purple/violet.

Question 9

Chlorine with water.

Answer 9

Chlorine water (solution) formed. Hydrochloric & chloric(I) acid formed. Both are colourless.
Cl2 + H2O -> HCl + HClO

Question 10

Chlorine with cold alkali.

Answer 10

Cl added to cold dilute aq. sodium hydroxide. Products= sodium chloride and sodium chlorate(I)/sodium hypochlorite.
Cl2 + 2NaOH -> NaCl + NaClO + H2O
Sodium chlorate(I) mainly used in household bleach and industry.
Disproportionation reaction.

Question 11

Chlorine with hot alkali.

Answer 11

Chlorine added to hot concentrated sodium hydroxide solution. Sodium chloride and sodium chlorate formed.
3Cl2 + 6NaOH -> 5NaCl + NaClO3 + 3H2O
Sodium chlorate(V) formed used in bleaching and as weed killer.
Disproportionation reaction.
Br and I react in similar ways.