8.2 The halogens

appearance and state of fluorine at RTP

pale yellow gas

appearance and state of chlorine at RTP

pale green gas

appearance and state of bromine at RTP

red-brown liquid

appearance and state of iodine at RTP

shiny grey-black solid

appearance and state of astatine at RTP

unknown

explain why the boiling point of group 7 elements increases down the group

more electrons

stronger London forces

more energy required to break the London forces

boiling point increases

state the most common type of reaction of the halogens

redox

why are halogens oxidisng agents

high electronegativity and electron affinity

can remove electrons from other elements/ high tendency to accept electrons

how to tell solutions of iodine and bromine in water

add cyclohexane (organic, non-polar solvent) and shake the mixture

iodine becomes a deep violet colour

chlorine solution + bromide ions =

chloride ions + bromine

orange

chlorine solution + solution of iodide ions =

chloride ions + iodine

violet

bromine solution + solution of iodide ions =

bromide ions + iodine

violet

iodine solution + solution of chloride ions

no reaction

iodine solution + solution of bromide ions

no reaction

which type of reaction shows that the reactivity of the halogens decreases down the group

halogen-halide displacement reactions

explain why reactivity decreases down the group and the halogens become weaker oxidising agents down the group

atomic radius increases

more inner shells so shielding increases

less nuclear attraction to capture an electron from another species

reactivity decreases

define disproportionation

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

formula of the reaction of chlorine with water including state symbols

Cl₂(aq) + H₂O(l) = HClO(aq) + HCl(aq)

formula of the reaction of chlorine with cold dilute aqueous sodium hydroxide including state symbols

Cl₂(aq) + 2NaOH(aq) = NaClO(aq) + NaCl(aq) + H₂O(l)

risks of chlorine use in water

chlorine in drinking water can react with organic hydrocarbons (eg. methane) formed from decaying vegetation. chlorinated hydrocarbons are formed which are linked to cancer

general formula of a precipitation reaction of aqueous halide ions with aqueous silver ions

Ag⁺(aq) + X^-(aq) = AgX (s)

colour of Cl₂ solution in water

pale green

colour of Br₂ solution in water

orange

colour of I₂ solution in water

brown