Group 7

Question 1

Explain how and why the atomic radius changes changes for the group 7 elements

Answer 1

The atoms get bigger down the group because shielding increases down group

Question 2

Explain how and why the electronegativity changes for group 7 element

Answer 2

Electronegativity decreases down the group
Depends on the correct balance of 3 factors:
- a greater nuclear charge withdraws electrons more strongly
- A shorted atomic radius will also help withdraw electrons more strongly
- More shielding will reduce the amount of electrons withdraw

Question 3

Explain the trend in oxidising ability of the halogens

Answer 3

Oxidising power decreases down group 7. Fluorine accepts electrons most easily so is the strongest oxidising agent.

Question 4

Describe the experimental evidence that confirms the oxidising trend

Answer 4

Displacement reactions. The element highest up group 7 should form a halide ion as greatest oxidinging agent whereas the halogen lowest down group 7 should form a halogen molecule

Question 5

State the trend in reducing abilities of the halide ions

Answer 5

Reducing power increases down group 7 as fluoride ions are least willing to release their additional electron

Question 6

How is the trend in reducing abilities in group 7 linked to ionic radius

Answer 6

Fluorine is the worst reducing agent as smallest ionic radius as least shielding so strongest attraction between nucleus and outer electrons

Question 7

Describe how halide ions are identified using silver nitrate

Answer 7

Add nitric acid to remove any carbonate ions which may be present as could alter results
Add silver nitrate:
- fluoride NVC
- chloride white precipitate
- bromide cream precipitate
- iodide yellow precipitate
Then add dilute ammonia:
- chloride ions the white precipitate dissolves
- bromide cream precipitate remains
-iodide ions yellow precipitate remains
Add concentrated ammonia :
- bromide ions cream precipitate dissolves
- iodide ions yellow precipitate remains

Question 8

Describe how chlorine reacts with water

Answer 8

Cl2(g) + H2O(l) —>___<HClO(aq) + HCl(aq)
Reversible reaction
disproportionation reaction as Cl starts of 0 oxidation and gets reduced to -1 in HCl and oxidised to +1 in HClO at the same time
Used in swim pools as HClO oxidising agent and kills bacteria by oxidinging them
2Cl2(g) + H2O(l) —-> 4HCl(aq) + O2(g)
Occurs in bright sunlight so chlorine rapidly lost in outdoor swimming pools
pale green to colourless
NaClO(s) + H2O(l) —> <Na+(aq) + OH-(aq) + HClO (aq)
Revsible
Indirect chlorination of pools

Question 9

Describe how chlorine reacts with alkali

Answer 9

Cl2(g) + 2NaOH(aq) —-> NaClO(aq) + NaCl(aq) + H2O (l)
NaClO is an oxidising agent and a component of household bleach
Disproportionation reaction

Question 10

Uses of chorine

Answer 10

Poisonous and extremely dangerous in high concentrations but used in treatment of drinking water and swimming pools as in very low concentrations chlorine and it’s derivatives are safe for humans and kill bacteria

Question 11

Trend of melting and boiling point in group 7

Answer 11

Increase down group as IDD forces so dependent on size of molecule