Give two examples to show the anomalous behaviour of fluorine.

Explanation

The anomalous behaviour of fluorine is due to its 1. small size 2. highest electronegativity 3. low F - F bond dissociation enthalpy and 4. non-availability of d -orbitals in its valence shell.
(i) Fluorine is the most electronegative element with -1 oxidation state. With the exception of HOF, it does not exhibit +1 oxidation state. It is due to non-availability of a more electronegative element than fluorine, with which it can share its unpaired electrons. Moreover, due to absence of d -orbitals,it cannot show higher positive oxidation states of +3 , +5 and +7 which ( + 1 , +3 , +5 and + 7 ) are shown by other halogens, besides - 1. As a result, fluorine does not show dispropor-tionation reactions in alkaline medium like any other halogen. (ii) F forms the strongest H -bonds, owing to its small size and high electronegativity. As a result, HF is a liquid with a boiling point of 293K while all other hydrogen halides are gases at room temperature.