3.1.1 GROUP 7, THE HALOGENS

Question 1

Describe and explain the trend in reactivity down group 7

Answer 1

• Reactivity decreases down the
  group
• Atomic radius increases due to
  increased number of shells
• Greater shielding between
  positive nucleus and an outer
  electron, decreasing the
  electrostatic attraction felt.

Question 2

What are the colours of the halogens? (vapours and solid)

Answer 2

Fluorine - colourless/pale yellow
Chlorine - yellow/green
Bromine - Brownish solution
Iodine - grey crystals/ purple vapour

Question 3

What is the state of each halogen at room temperature?

Answer 3

Fluorine - gas
Chlorine - gas
Bromine - liquid
Iodine - solid
Astatine - solid

Question 4

General properties of the halogens

Answer 4

• Diatomic
• Toxic
• Volatile
• Simple molecular structures
• Very soluble (in water + other)
• React with aluminium to produce
  WHITE TRIHALIDES

Question 5

What is a commercial use of iodine?

Answer 5

As an antibacterial

Question 6

What is electronegativity?

Answer 6

The tendency of an atom to attract a bonding pair of electrons in a covalent bond

(Measured with the Pauling scale)

Question 7

Name the most and least electronegative elements

Answer 7

Most - Fluorine
Least - Francium and Caesium

Question 8

What is the trend in electronegativity across the periodic table?

Answer 8

Electronegativity increases up groups and along periods

Question 9

Describe and explain the trend in electronegativity down group 7

Answer 9

• It decreases down the group
• Larger atomic radius, more shells
• Greater shielding
• Weaker attraction between -
  positive nucleus and electron pair

Question 10

Describe and explain the trend in melting and boiling point down group 7

Answer 10

• Increases down the group
• Larger molecules
• Greater van der waals forces

Question 11

Describe and explain the trend in first ionisation energy down group 7

Answer 11

• Decreases down the group
• Larger atomic radius, more shells
• Greater shielding
• Weaker attraction between outer
  electron and positive nucleus
• More easily removed

Question 12

What are the colours of the halogens in organic solvents?

Answer 12

**

Question 13

Write the equations for halogens acting as oxidising agents, and halides acting as reducing agents

Answer 13

X2 + 2e- —— 2X-
^ Oxidising agent

2X- ——- X2 + 2e-
^Reducing agent

Question 14

How does the oxidising ability of the halogens change down the group?

Answer 14

It decreases
Larger atomic radius, more shells
Greater shielding
Less electrostatic force felt between nucleus and another electron in a compound

Question 15

Describe how the reducing ability of the halogens change down the group

Answer 15

Reducing ability increases
Greater shielding (Ar + shells)
Less attraction between outer electron and positive nucleus
Easier to lose an electron, as less energy is required to remove it

Question 16

Why do redox reactions not happen when fluorine and chlorine react with concentrated sulfuric acid?

Answer 16

Fluorine and Chlorine are not strong enough oxidising agents

(instead undergo reaction with H2SO4 as a proton donor)

Question 17

Write a general form for the (acid) reaction between halide ions and concentrated sulfuric acid

Answer 17

X- + H2SO4 —— HX + NaHSO4

e.g. NaCl + H2SO4 – HCL + NaHSO4

Question 18

What are the properties of hydrogen halides?

Answer 18

• Colourless gases at room
  temperature
• Form steamy fumes in moist air

Question 19

What are the properties of hydrogen sulfide?

Answer 19

• Colourless
• Corrosive
• Flammable

Question 20

What happens in the reaction between bromide ions and sulfuric acid?

Answer 20

Bromide ions reduce SO4 to SO2, and are oxidised to neutral Br2 molecules, producing water as well

H2SO4 + 2Br- + 2H+ – SO2 + Br2 + 2H2O

Question 21

State the charge on the hydrogen sulfate ion, and the oxidation numbers on the elements involved

Answer 21

HSO4 [-1]
H + 1
S - 2
O -2

Question 22

Describe what happens when concentrated sulfuric acid reacts with iodide ions

Answer 22

• Sulfuric acid is reduced from S+6
  then to S+4, then to neutral sulfur.
• Sulfur is then reduced to -2 in
  hydrogen sulfide, if there is
  enough iodine to reduce all the
  sulfur.
• Water is also produced
• Iodine acts as a reducing agent and is oxidised to I2 molecules

Question 23

What is the overall equation for when concentrated sulfuric acid reacts fully with iodide ions?

Answer 23

H2SO4 + 8I- + 8H+ – 4I2 + H2S + 4H2O