Group 7 - Inorganic (4)

Question 1

Explain the trend in melting and boiling point of Group 7 elements (3)

Answer 1

1. The melting and boiling point increases down the group
2. This is because an increase in the number of electrons leads to stronger temporary dipole-dipole interactions (London forces)
3. Therefore, more energy is needed to overcome these forces and separate the molecule

Question 2

Define Electronegativity

Answer 2

1. Electronegativity is the ability of an atom to attract a pair of electrons towards itself in a covalent bond.

Question 3

Explain the trend in electronegativity of group 7 elements (4)

Answer 3

1. Electronegativity decreases down the group
2. An increase in atomic radius results in a larger distance between the outermost electron and the nucleus, resulting in a smaller force of electrostatic attraction
3. Although nuclear charge increases down the group, this is compensated by the increase in electron shielding
4. Overall, the atom becomes less able to attract the bonding pair of electrons and so the electronegativity decreases

Question 4

Explain the trend in reactivity of Group 7 elements

Answer 4

1. Reactivity decreases down the group
2. Because most reactions of the halogens involve them acting as oxidising agents and gaining electrons
3. Therefore, An increase in atomic radius results in a larger distance between the outermost electron and the nucleus, resulting in a smaller force of electrostatic attraction
4. Although nuclear charge increases down the group, this is compensated by the increase in electron shielding
5. Overall, the atom becomes less able to attract the bonding pair of electrons and so the electronegativity decreases and so the reactivity decreases.

Question 5

What are the Halogen/Halide displacement reactions?

Answer 5

1. A more reactive halogen can displace a less reactive halogen from one of its compounds. Therefore, it is used to show the reactivity of Group 7 Halogens
2. The reactions take place in aqueous solutions. An organic solvent (cyclohexane) is used to show a more vivid colour change as the halogens are more soluble in cyclohexane.
3. Without an organic solvent, the colour changes can look similar with the different halogens as the colour also depends on their concentrations

Question 6

Describe the reactions of halogens with metals

Answer 6

1. On heating, halogens react with metals to form halides in the -1 oxidation state (from 0 to -1 so reduction)
2. Metals with variable oxidation states will adopt a different state depending on the Oxidising power of the halogen
3. Metal + halogen = Metal halide

Question 7

Define Disproportionation

Answer 7

1. The simultaneous oxidation and reduction of an element in a chemical species

Question 8

State the disproportionate reaction of chlorine with water

Answer 8

1. Chlorine + water = HCl + HClO (Chloric (I) acid)

0 -1 +1

Question 9

State the disproportionation reaction of chlorine with cold alkali (sodium hydroxide) (include oxidation no.)

Answer 9

halogen + sodium hydroxide (cold) = sodium halide + sodium halate [I] (NaXO) + water
0 -1 +1

Question 10

State the disproportionation reaction of chlorine with hot alkali (sodium hydroxide) (include oxidation no.)

Answer 10

Halogen + Sodium hydroxide = Sodium halide + Sodium halate [V] (NaXO3) + water
0 -1 +5

Further disproportionation occurs

Question 11

State and explain the reactions of Group 1 halides with sulphuric acid to illustrate the trend in reducing ability of halides

Answer 11

1. (sodium) Halide + Sulphuric acid = Hydrogen halide (HCl) + Halogen + Sulphur dioxide + Sulphur + Hydrogen Sulphur
   +6 +4 0 -2

Question 12

Acidic nature of Hydrogen Halides:
State the equations of Hydrogen halides
(i) with ammonia
(ii) with water (to produce acids)

Answer 12

i) NH₃ (g) + HCl (g) = NH₄Cl (s)

ii) HCl + H₂O = H₃O⁺ + Cl⁻