Halides and halide complexes

Almost all elements create thermodynamically stable halides. The general stability sequence is F>Cl>Br>I, that in covalent compounds follows the supposed order of bond strengths, and in ionic compounds which of lattice energies. The thermodynamic stability of fluorides (and the kinetic reactivity of F2) is also aided through the weak F-F bond. Several halides can be made through direct combination, but fluorinating agents like ClF₃ are sometimes employed in preference to F₂, that is very difficult to handle.

The bonding and structural trends in halides follow identical patterns to those in oxides. Several nonmetallic elements create general molecular compounds where halogen atoms each have a single bond to another element. This is right also for metals in high oxidation states (example UF₆ and TiC_l4). The compounds might be solids, gases or liquids, with volatility in the order F>Cl>Br> I as expected from the strength of van der Waals' forces. HF is exceptional due to strong hydrogen bonding, in the hydrogen halides. HF is a weak acid in water, another HX compounds being strong acids.