Group 7

Question 1

Trend in electronegativity

Answer 1

• Decreases
~ shielding increases
~ less attraction between outer e and nucleus

Question 2

Trend in boiling point

Answer 2

• Increase
~ vdw forces
~ strength increase with mr
~ more energy required to break these bonds

Question 3

Trend in oxidising ability

Answer 3

• Good oxidising agents
~ accept e and are reduced

• Oxidising power decreases
~ greater shielding and atomic radius
~ harder to gain e

• Cl2 displace Br^- and I^-
Br^- displaces I^-
I^- displaces none

Question 4

Trend in reducing ability

Answer 4

• Increases down group
• Greater shielding and atomic radius
~ easier to lose e

Question 5

Reactions of NaF & NaCl with sulfuric acid

Answer 5

NaF + H2SO4 —> NaHSO4(s) + HF

NaCl + H2SO4—> NaHSO4(s) + HCl
White fumes of HCl

Question 6

NaBr and H2SO4

Answer 6

NaBr + H2SO4—> NaHSO4 + HBr
(s) (l) (s) (g)

2HBr+H2SO4—>Br2+SO2+2H2O
(g) (g)
Reddish brown gas of Br2

Question 7

NaI and H2SO4

Answer 7

•NaI + H2SO4 —> NaH2SO4 + HI
(s) (l) (s) (g)
•2HI + H2SO4 -> I2+ SO2 + 2H2O
(g) (l)
~Purple vapour of I2

• 6HI + H2SO4 -> 3I2 + S + 4H2O
(s)
~ yellow solid of s

• 8HI + SO2 -> 4I2 + H2S + 4H2O
~ egg smell of H2S

Question 8

How to identify and distinguish between halide ions

Answer 8

• Sliver nitrate
White, cream, yellow