Halides
Born-Haber cycle for
the synthesis of a halide compound:
In general, fluorine stabilises high oxidation
state compounds.
Explaination of trends:
1. Weak F-F bond (also kinetic argument).
2. Strong B(E-F) bonds, (F > Cl > Br > I).
3. High electron affinity, cf. DHf[X-(g)].
4. High lattic energy, small F-
ion (F>Cl>Br>I), Kapustinskii approximation.
Low to intermediate oxidation states. EF2
unstable with respect to disproportionation (eg. SF2).
Covalency increases with oxidation state.
Covalency increases down the series F 
I.
Lower oxidation state tends to be formed with
Br and I.
High oxidation state fluorides tend to be molecular.