existence of halogens as diatomic molecules and explanation of the trend in the boiling points of Cl₂, Br₂ and I₂, in terms of induced dipole–dipole interactions (London forces) (see also 2.2.2k)

the outer shell s²p⁵ electron configuration and the gaining of one electron in many redox reactions to form 1– ions

Throughout this section, explanations of redox reactions should emphasise electron transfer and oxidation number changes and include full and ionic equations (see also 2.1.5 Redox).

the trend in reactivity of the halogens Cl₂, Br₂ and I₂, illustrated by reaction with other halide ions

Including colour change in aqueous and organic solutions.

explanation of the trend in reactivity shown in (c), from the decreasing ease of forming 1– ions, in terms of attraction, atomic radius and electron shielding

explanation of the term disproportionation as oxidation and reduction of the same element, illustrated by:

(i) the reaction of chlorine with water as used in water treatment
(ii) the reaction of chlorine with cold, dilute aqueous sodium hydroxide, as used to form bleach
(iii) reactions analogous to those specified in (i) and (ii)

the benefits of chlorine use in water treatment (killing bacteria) contrasted with associated risks (e.g. hazards of toxic chlorine gas and possible risks from formation of chlorinated hydrocarbons)

the precipitation reactions, including ionic equations, of the aqueous anions Cl^–, Br^– and I^– with aqueous silver ions, followed by aqueous ammonia, and their use as a test for different halide ions.

Complexes with ammonia are not required other than observations.
PAG4 (see also 3.1.4a)