Describe anomalous behaviour of fluorine with the other elements of group 17 with reference to :
(a) Hydrogen bonding (b) Oxidation state
(c) Polyhalide ions.

Explanation

Anomalous behaviour of flurone with the other elements of group 17 : Fluorine shows anomalous behaviour with the other elements of group 17 due to : (1) small size, (2) high electronegativity and (3) non-availability of - orbitals in its valence shell.
(a) Hydrogen bonding : O account of high electronegativity of fluorine atom, extensive hydrogen bonding occurs in HF molecule while it is absent in HCl, HBr and HI. The presence of hydrogen bonding in HF is explained as under hydrogen bonding in HF is explained as under :
(1) HCl,HBr and HI are gaseous while HF is a liquid with an abnormally high boiling points.
(2) HF forms a number of compounds containing `HF_(2)^(-)` ion (e.g., `KHF_(2)`) while such compounds are not given by other HX molecules.
`HF* * * * * * * * H-F * * * * * * * *underset("H-bond")underset(uarr)(H)-F" "(HF)_(n)`
(b) Oxidation state : Due to maximum electronegativity of fluorine, it shows only a negative oxidation state of - 1. It does not show any positive oxidation state. The other members of group 17 show negative as well positive oxidation states of `+1,+3," "+5and +7`.
(c) Polyhalide ions : Because of the absence of d-orbitals in its valence shell, fluorine does not combine with `F^(-)` ions to give polyhalide ions (like `F_(3)^(-)` ) while other members of group 17 give such polyhalide ions like `Cl_(3)^(-),Br_(3)^(-),I_(3)^(-),I_(5)^(-)` etc., because they contain d-orbilats and also there electronegativity is low.