2.3 Group 7

Question 1

Trend in atomic radius down group 7

Answer 1

Increases
- Main shells and shielding increases
- Weaker nuclear attraction to the outer electrons

Question 2

Why is the radius of halide ions greater than halogen atoms?

Answer 2

• Ions have more electrons
• Same number of protons
• Weaker nuclear attraction in ions

Question 3

Trend in boiling point down group 7

Answer 3

Increases (halogens become less volatile)
- Larger molecules, more electrons
- Stronger van der Waals forces
- More energy needed

Question 4

Trend in electronegativity down group 7

Answer 4

Decreases
- More main shells and shielding
- Less attraction between shared pair and nucleus

Question 5

Trend in first ionisation energy down group 7

Answer 5

Decreases
- More main shells and shielding
- Less nuclear attraction to outer electron
- Less energy needed to remove it

Question 6

Colour of chlorine

Answer 6

Green

Question 7

Colour of bromine

Answer 7

Red-brown

Question 8

Colour of Iodine

Answer 8

Black

Question 9

State of chlorine (at room temperature)

Answer 9

Gas

Question 10

State of bromine (at room temperature)

Answer 10

Liquid

Question 11

Colour of chlorine in aqueous solution

Answer 11

Pale green

Question 12

Colour of bromine in aqueous solution

Answer 12

Orange

Question 13

Colour of iodine in aqueous solution

Answer 13

Brown

Question 14

Colour of chlorine in cyclohexane

Answer 14

Pale green

Question 15

Colour of bromine in cyclohexane

Answer 15

Orange

Question 16

Colour of iodine in cyclohexane

Answer 16

Pink-purple

Question 17

What are the best solvents for halogens?

Answer 17

Non-polar solvents like cyclohexane

Question 18

Trend in solubility down group 7

Answer 18

Solubility decreases

Question 19

Are halogens oxidising agents or reducing agents?

Answer 19

Oxidising agents (they accept electrons to form halide ions)

Question 20

Trend in oxidising power down group 7

Answer 20

Decreases
- More main shells and shielding
- Less nuclear attraction to electron being accepted
- Less ability to gain electrons

Question 21

Disproportionation

Answer 21

A redox reaction in which the same element is both oxidised and reduced

Question 22

What is formed when chlorine reacts with water?

Answer 22

HCl + HClO (HClO decomposes in sunlight to form HCl and O₂)

Question 23

HClO

Answer 23

Chloric (1) acid

Question 24

Colour change with litmus paper/universal indicator: HClO

Answer 24

Indicator is bleached

Question 25

Benefits and risks of using Cl₂ in water treatment

Answer 25

Benefit: Kills bacteria at non-toxic levels
Risk: Toxic in larger quantities

Question 26

How are sodium chloride, sodium chlorate(1) and water produced from Cl₂?

Answer 26

Reacting Cl₂ with cold dilute sodium hydroxide solution

Question 27

Uses of NaCl, NaClO, and H₂O solution

Answer 27

• As a bleach
• To kill bacteria

Question 28

Test for halide ions

Answer 28

• Make a solution of the test substance
• Add dilute nitric acid (to remove other ions)
• Add silver nitrate solution

Question 29

Positive test for Cl⁻

Answer 29

White precipitate forms (AgCl)

Question 30

Positive test for Br⁻

Answer 30

Cream precipitate forms (AgBr)

Question 31

Positive test for I⁻

Answer 31

Yellow precipitate forms (AgI)

Question 32

Why do F⁻ ions not form a precipitate with silver nitrate?

Answer 32

AgF is soluble in water