Describe anomalous behaviour of fluorine with the other elements of group 17 wilh reference to :
(a) Hydrogen bonding
(b) Oxidation state
(c) Polyhalide ions
Fluorine exhibits anomolous behaviour as compared to other halogens atom in the group. The reasons for anomolous behaviour of fluorine are as follows.
(i) The smallest size of fluorine
(ii) The highest electronegativity
(iii) Low bond dissociation enthalphy of F- F. bond
(iv) Non availbility of d-orbitals in the valence shell
(a) Hydrogen bonding : Fluorine has the highest electronegativity other halogens. Fluorine forms strong hydrogen bonding in its hydrides unlike other halogens, because H-F bond is highly polar in nature. Hence HF is a liquid while other hydrogen halide are gauses at room temperature.
(b) Oxidation state : Fluorine is smallest in size and highly electronegativity thus fluorine shows only one oxidation state –1, while other halogen show variable oxidation states like –1,+1,+3,+5 and +7
(c) Polyhalides ions : Fluorine is smallest in size and d-orbitals are not availble in the valence shell of fluorine. hence it has no tendency to form polyhalide in where as other halogen form polyhalide ions like
`Cl_3^-, Br_3^-, I_3^-`