Group 7

Question 1

What are all the group 7 element appearance and state at room temperature?

Answer 1

Fluorine - pale yellow gas
Chlorine - pale green gas
Bromine - dark red liquid
Iodine - grey solid but sublimes into a purple vapour when slightly heated
Astatine - black solid

Question 2

What is the trend in atomic radius going down group 7 and why?

Answer 2

Atomic radius increases down group 7 because of the additional electrons in each shell

Question 3

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

Answer 3

Melting and boiling point increases down group 7 because the atoms get bigger down the group which means more van der waals forces and the strength of the van der waals forces increase down group 7 which requires more energy to overcome.

Question 4

What is the trend in electronegativity going down group 7 and why?

Answer 4

Electronegativity decreases down group 7 because the size of the atom gets bigger due to increased shielding which makes it easier to attract a pair of electrons in a covalent bond.

Question 5

What is the trend in bond enthalpy going down group 7 and which element is an exception and why?

Answer 5

Bond enthalpy decreases down group 7 because shielding increases which outweighs the increase in nuclear charge.

Fluorine atoms are small and are so close together that the lone pairs of electrons around each atom repel each other so the bond is weakened which results in a very low bond enthalpy.

Question 6

What is the trend in reactivity down group 7?

Answer 6

Reactivity decreases down group 7 because atomic radius and shielding increases which makes it harder to gain an electron because of the weaker electrostatic force between the positive nuclei and negative electron.

Question 7

What is the trend in the 1st ionisation energy down group 7?

Answer 7

The ionisation energy decreases down group 7 because shielding increases down group 7 which makes it easier to lose the outer electron.

Question 8

What are oxidising agents?

Answer 8

Electron acceptors that are being reduced themselves.

Question 9

What is the trend in oxidising power down group 7?

Answer 9

Oxidising power decreases down group 7 because shielding and atomic radius increase down group 7 which makes it harder to attract an electron due to the weaker electrostatic force.

Question 10

How is bleach made?

Answer 10

Via a disproportionation reaction
- Mixing chlorine and sodium hydroxide forms sodium chlorate (I) solution which is bleach.

Question 11

Write out the equation for making bleach.

Answer 11

2NaOH(aq) + Cl2(g) -> NaClO(aq) + NaCl(aq) + HzO(l)

Question 12

Why is making bleach a disproportionation reaction?

Answer 12

Cl2(g) has an OS of 0
Cl in NaClO has an OS of +1
Cl in NaCl has an OS of -1
Chlorine has been simultaneously oxidised and reduced.

Question 13

What are the uses of sodium chlorate (I)?

Answer 13

Cleaning agents as bleach
Treating water
Bleaching paper and fabrics

Question 14

How can bacteria in water be killed?

Answer 14

By adding chlorine

Question 15

What happens when chlorine is added to water

Answer 15

It produces chlorate (I) ions (ClO-) that kill bacteria.

Question 16

What is the equation of water sterilisation?

Answer 16

H2O(l) + Cl2(g) -> 2H+(aq) + Cl-(aq) + ClO-(aq)

Question 17

Why is water sterilisation a disproportionational reaction?

Answer 17

Cl2(g) has an OS of 0
Cl-(aq) has an OS of -1
Cl in ClO-(aq) has on OS of +1
Chlorine is being simultaneously reduced and oxidised.

Question 18

What happens to water sterilisation in the presence of sunlight?

Answer 18

Sunlight can decompose chlorinated water but no ClO- is made.

Question 19

What is the equation for water sterilisation in the presence of sunlight?

Answer 19

2H2O(l) + Cl2(g) -> 4H+(aq) + 2Cl-(aq) + O2(aq)

Question 20

What are the advantages and disadvantages of chlorinating drinking water?

Answer 20

Advantages:
- Destroy diseases causing microorganisms
- Long lasting so reduces bacteria build up further down the supply
- Reduces the growth of algae which can discolour water and give it a bad taste and smell

Disadvantages:
- Chlorine gas is toxic and irritates the respiratory system
- Liquid chlorine causes severe chemical burns to the skin
- Chlorine can react with organic compounds present in the water and make chloroalkanes which have been linked to causing cancer