Discuss anomalous behaviour of fluorine.

Explanation

Fluorine shows anomalous behaviour due to :
(i) Small size
(ii) High ionisation enthalpy
(iii) Absence of d-orbitals in valance shell
(iv) High positive electrode potential Fluorine shows (-1) oxidation state only while other elements show (+1), (+3) (+5) and (+7) oxidation states. HF is liquid due to H-bonding while HCl, HBr and HI are gaseous in state. Fluorine does not form poly fluorides, for
example : `F_3` is not known. This is due to absence of d-orbitals in valance shell.
Fluorine forms only one oxoacid (HOF) while other halogens form number of oxoacids. The maximum covalency of fluorine is one due to absence of d-orbital in valance shell while other halogens show covalence of 7.
Hydrofluoric acid is a dibasic acid (`H_2F_2`) while other hydrohalic acids are monobasic. `F_2` is highly reactive due to low bond (F - F) dissociation enthalpy.
Fluorine forms hexafluoride (`SF_6`) while other halogens do not form hexahalides with sulphur.