Question

What is the common oxidation number of bromine in its compounds?

Answer 1

Usually `-I`, but not always.

Explanation:

As a halogen, bromine commonly exhibits a `-I` oxidation state (i.e. valency) in its ionic compounds as the bromide anion, but it does not do so exclusively. Bromine does form so-called interhalogen compounds, e.g `BrF_3`, or even `BrF` (and what is the formal oxidation state of `Br` in these two examples; they are different in each case). Oxidation numbers of `+I`, `+III`, `+V`, and `+VII` are known with its oxides, and oxoanions.

Both valency and oxidation number are of course a formalism; can you assign the oxidation number of bromine in its elemental state?