Group 7

Explain the trend in electronegativity

DECREASES DOWN GROUP

• Increased shielding and atomic radius, which means attraction between the electrons and nucleus has weakened, and the atoms ability to attract a shared pair of electrons towards itself in a covalent bond decreases

Explain the trend in boiling point

INCREASES DOWN GROUP

• Size of molecule increases, van de waal forces become stronger so take more energy to overcome

What is oxidising ability?

Ability of an atom to attract/ gain electrons (the substance itself is reduced)

Explain the trend in oxidising ability

DECREASES DOWN GROUP

• Atomic radius and shielding increases so the attraction between nucleus and electron decreases, and the ability for the nucleus to attract electrons decreases

What can halogens do?

Displace the halide ions below it in the periodic table

What can Cl₂, Br₂ and I₂ displace?

Cl₂- Br^- and I^-

Br₂- I^-

I₂- nothing

What is reducing ability?

The ability of an atom to donate/ lose electrons (the substance itself is oxidised)

Explain the trend in reducing ability

INCREASES DOWN GROUP

• Atomic radius and shielding increases, so nuclear attraction to electrons weakens and it is easier to lose an electron

• Halide ions become better reducing agents as you go down the group

How do solid sodium chloride and solid sodium fluoride react with conc sulphuric acid and what is the observation?

NaX + H₂SO₄ → NaHSO₄ + HX
Steamy/ misty fumes

How does solid sodium bromide react with conc sulphuric acid?

• NaBr + H₂SO₄ → NaHSO₄ + HBr

• 2HBr + H₂SO₄ → Br₂ + SO₂ + 2H₂O

Brick-red steamy fumes

How does solid sodium iodide react with conc sulphuric acid?

• NaI + H₂SO₄ → NaHSO₄ + HI

• 2HI + H₂SO₄ → I₂ + SO₂ + 2H₂O

• 6HI + SO₂ → 3I₂ + H₂S + 2H₂O

Bad egg smell from h2s

What solution is used to identify between halide ions?

Acidified silver nitrate solution

Why is silver nitrate solution acidified?

To remove any excess ions which could mask the results

What colour precipitates form?

Cl^- white precipitate
Br^- cream precipitate
I^- yellow precipitate

Why may ammonia solution be added?

Sometimes it is hard to distinguish between the colours of the precipitate, so this helps with identification

What do we observe when dilute ammonia is added?

Cl^- precipitate dissolves
Br^- no change
I^- no change

What do we observe when conc ammonia solution is added?

Cl^- ppt dissolves
Br^- ppt dissolves
I^- no change

What is the equation for chlorine reacting with water?

Cl₂ + H₂O → ClO^- + 2H⁺ + Cl^-

What is the equation for chlorine reacting with water in the presence of UV light?

2Cl₂ + 2H₂O → 4Cl^- + 4H⁺ + O₂

What are the advantages of using chlorine in water treatment?

• Kills bacteria/ pathogens

• Prevents algal growth

• Prevents reinfection of water as remains in water

What are the disadvantages of chlorine use?

• Toxic in large quantities; can harm respiratory system

• Can cause chemical burns

• Chlorinated hydrocarbons can cause cancer

What is the reaction of chlorine with dilute aqueous cold sodium hydroxide?

Cl₂ + 2NaOH → NaClO + NaCl + H₂O

NaClO used in production of bleach which kills bacteria

Give an equation for the reaction of solid sodium bromide with concentrated sulfuric acid to form bromine.

2NaBr (s)+3H_2​SO₄​→ 2NaHSO₄​(aq)+Br_2​(l)+SO_2​(g)+2H_2​O (l)

what is the equation between silver chloride and ammonia?

AgCl + 2NH₃ → Ag(NH₃)₂ + Cl^-