Identify the molecule in which the arrangement of electron pairs around the central atom is octahedral and…

Identify the molecule in which the arrangement of electron pairs around the central atom is octahedral and shape is not octahedral.
  1. $\mathrm{SF}_6$
  2. $\mathrm{XeF}_6$
  3. $\mathrm{BrF}_5$
  4. $\mathrm{XeO}_2 \mathrm{~F}_4$

Solution

The arrangement of electron pairs around the central atom is octahedral and shape is not octahedral can be identified with the help of presence of lone pair (lp) of electrons and bond pair $(b p)$ of electrons associated with the central atom. The structure of given species are : (i) $\mathbf{S F}_6$ Central atom sulphur has 6 valence electrons, which are bonded with 6F-atoms, thus have octahedral shape.
(ii) $\mathbf{X e F}_{\mathbf{6}}$ Central atom, Xe have 8 valence electrons, out of which 6 are bonded with $6 \mathrm{~F}$-atoms and one $l p$ of electron is associated with Xe-atom. Thus, has distorted octahedral shape.
$\mathbf{B r F}_5$ Central atom $(\mathrm{Br})$ have 7 valence electrons, out of which 5 are bonded with $5 \mathrm{~F}$-atoms and one $l p$ of electron is associated with $\mathrm{Br}$-atom having square pyramidal shape.
$\mathbf{X e O}_{\mathbf{2}} \mathbf{F}_{\mathbf{4}}$ Central atom, Xe have 8 valence electrons, out of which 4 are bonded through 4-sigma $(\sigma)$ bonds with 4F-atoms and two oxygen atoms each having one sigma $(\sigma)$ bond and one pi $(\pi)$ bond is associated with Xe-atom. Thus, has octahedral shape.
Hence, option (c) is the correct answer.

Asked in: AP EAMCET 2019 (21 Apr Shift 1)

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