Electron affinity : Electron affinity of chlorine, bromine and iodine decrease as the size of the atom increases. The electron affinity of fluorine is, however, lower than that of Cl and Br , because of its small size as a result of which inter-electronic repulsions present in its 2p subshell are comparatively large. Thus chlorine has the highest electron affinity.

The decreasing order of electron affinity is Cl > F > Br > I.

Oxidation states : All the halogens show an oxidation state of –1. Fluorine being the most electronegative element always shows an oxidation state of –1 while other halogens also show positive oxidation states up to a maximum of +7 (i.e. +1, +3, +5 and +7) due to the availability of vacant d -orbitals in the valence shell of these atoms. Some halogens also show +4 and +6 oxidation states in oxides and oxy acids.

Nature of bonds : All the halogens have seven electrons in the valence shell and hence require one more electron to acquire the nearest inert gas configuration either by gaining an electron from the metallic atom to form halide, ion, or by sharing an electron with an electronegative element. Thus, halogens form both ionic and covalent compounds. The halides of highly electropositive metals are ionic while those of weakly electropositive metals and non-metals are covalent. The tendency to form ionic compounds decreases from F to I. Thus, F because of its high electronegativity forms ionic compounds even with less electropositive metals like Hg, Bi, Sn etc. while other halogens form only covalent compounds.