trends in properties

electronegativity down the group

electronegativity decreases

atomic radius increases because electron shielding increases

Less attraction between nucleus and electrons in the covalent bond

Boiling point down the group

Boiling point increases

Molecular structures

Atoms get larger and have more electrons

Strength of Van Der Waals between halogen molecules increases

Need more energy to break them

Halogens are

Oxidising agents

Oxidising ability of the halogens down the group

Oxidising ability decreases

atomic radius increases because electron shielding increases

Less attraction between nucleus and electrons on the reducing agent

Chlorine in solution

Green

Bromine in solution

Yellow

Iodine in solution

Brown

Halides are

Reducing agents

Reducing ability down the group

Reducing ability increases

Atomic radius increases because electron shielding increases

Less attraction between nucleus and outer electrons so electrons are donated more easily

Sodium fluoride and concentrated sulfuric acid

NaF (s) + H2SO4 (l) → NaHSO4 (s) + HF (g)

Misty fumes of HF

Sodium chloride and concentrated sulfuric acid

NaCl (s) + H2SO4 (l) → NaHSO4 (s) + HCl (g)

Misty fumes of HCl

Why isn't NaCl and NaF a redox reaction and what is it

F- and Cl- aren't strong enough reducing agents to reduce the S in H2SO4

It's an acid-base reaction

Sodium bromide and concentrated sulfuric acid

acid-base step

Br- is a strong enough reducing agent to reduce S to SO2

H2SO4 + 2H+ + 2Br- → SO2 + Br2 + 2H2O

SO2 is a colourless gas

sodium iodide and concentrated sulfuric acid

acid-base step

I- is a strong enough reducing agent to reduce S to SO2, H2S and S

redox equation for S

H2SO4 + 6H+ 6I- → S + 3I2 + 4H2O

H2SO4 + 8H+ + 8I- → H2S + 4I2 + 4H2O

H2S has a bad egg smell

S is a yellow solid

how to test for halides

Add nitric acid then add silver nitrate

Why is nitric acid added

To remove any carbonate ions which could give a false positive

Observations

Chloride - white precipitate

Bromide - cream precipitate

Iodide - yellow precipitate

why is ammonia solution added after

colours are difficult to distinguish

solubilities in ammonia

silver chloride precipitate soluble in dilute

silver bromide precipitate soluble in concentrated

silver iodide precipitate not soluble