Group 7 halogens

How does atomic radius change down group 7

Increases due to additional electron shells

How does reactivity of group 7 elements change down the group

Reactivity decreases due to additional shielding

How does first ionisation energy change down group 7

First ionisation energy decreases due to greater atomic radius and shielding

How does boiling point change down the group 7 halogens

Increases due to greater atomic mass, which increases the strength of van der vaals forces

Halogens are good ……… agents

Oxidising agents

How does oxidising power of halogens change down the group

Decreases due to greater atomic radius, which increases shielding which decreases their ability to attract electrons

How does the relative oxidising strength of the halogens affect their reactions with halide ions

A halogen will displace any halide ion beneath it in the periodic table

Halide ions are good ……..

Reducing agents

How does the reducing power of halide ions change down the group

Reducing power increases down the group due to a larger atomic radius causing more shielding. This makes electrons easier to lose

Redox reaction of Fluoride and Chloride ions with H2SO4

NaF + H2SO4 ——> NaHSO4 + HF

Redox reaction of bromide ions with H2SO4

NaBr + H2SO4 ——> NaHSO4 +HBr

2HBr + H2SO4 ——→ Br2 + SO2 + 2H2O

Redox reaction of Iodide ions with H2SO4

NaI + H2SO4 ——> NaHSO4 + HI

2HI + H2SO4 ——> Br2 + SO2 + 2H2O

6HI + H2SO4 —→ 3I2 + S + 4H2O

8HI + H2So4 —> 4I2 + H2S + 4H2O

Test for halide ions

Acidified silver nitrate

Why do you add HNO3 and not HCl when testing for halide ions

To remove CO3 (2-)

Adding HCl would produce Cl- ions, giving a false positive result

What happens (+equations) to each of the silver halide precipitates when dilute/conc NH₃ are added

AgCl dissolves in both dilute and conc

AgCl + 2NH₃ —> [Ag(NH₃)₂]⁺ +Cl^-

AgBr- only dissolves in conc

AgBr + 2NH3 —> {Ag(NH₃)₂}⁺ + Br^_

AgI will not dissolve in either

Reaction of chlorine with cold water

Produces Chlorate (I) ions and chloride ions

Cl2 + H2O —> HClO + HCl

Why is the reaction of chlorine with cold water a disproportionation reaction

Chlorine is both oxidised and reduced

Reaction of chlorine with water in the presence of UV light

2Cl2 + 2H2O —→ 4HCl + O2

Why is chlorine added to drinking water

Chlorate ions oxide microorganisms in water, health benefits outweigh the risks

Reaction of chlorine with cold, aqueous sodium hydroxide (Bleach production)

2NaOH + Cl2 —> NaClO + NaCl + H2O