By the following method you can predict the geometrical shape of species with only one central atom, without first drawing the Lewis structure :
Total number of electron pairs = (number of valence electrons $\pm$ electrons (for ionic) charge)/2
Number of bond electron pairs = number of atoms - 1
Number of electron pairs around central atom = total number of electron pairs - 3 [number terminal atoms (except H)]
Number lone pair = (number of central electron pairs - number of bond pairs)

How many of the following have trigonal bipyramidal shape based on this method?
$(a) P C l_{5} (b) N H_{3} (c) H_{2} O$ $(d) {C l O_{3}}^{-} (e) {I C l_{4}}^{-}$

Open in App

Solution

Step

Species 1 2(x) 3 4(E) VSEPR notation Structure
(a) $P C l_{5}$
$\frac{5 + (5 \times 7)}{2} = 20$
5 $20 - 15 = 5$ $5 - 5 = 0$ $A X_{5}$ trigonal bipyramidal
(b) $N H_{3}$
$\frac{5 + 3}{2} = 4$
3 $4 - 0 = 4$ $4 - 3 = 1$ $A X_{3} E$ trigonal pyramidal
(c) $H_{2} O$
$\frac{2 + 6}{2} = 4$
2 $4 - 0 = 4$ $4 - 2 = 2$ $A X_{2} E_{2}$ angular
(d) $C l O_{3}^{-}$
$\frac{7 + 18 + 1}{2} = 13$
3 $13 - 9 = 4$ $4 - 3 = 1$ $A X_{3} E$ Pyramidal
(e) $I C l_{4}^{-}$
$\frac{7 + 28 + 1}{2} = 18$
4 $18 - 12 = 6$ $6 - 4 = 2$ $A X_{4} E_{2}$ Square planar
All the structures determined by this new method is similar to that used by VSEPR theory and is widely acceptable.

Suggest Corrections

Similar questions

(X)

(Y)

I_{3}^{-}

X + Y

O F_{2}

A σ

M X_{3}

T -

Join BYJU'S Learning Program

	Step
Species	1	2(x)	3	4(E)	VSEPR notation	Structure
(a) $P C l_{5}$	$\frac{5 + (5 \times 7)}{2} = 20$	5	$20 - 15 = 5$	$5 - 5 = 0$	$A X_{5}$	trigonal bipyramidal
(b) $N H_{3}$	$\frac{5 + 3}{2} = 4$	3	$4 - 0 = 4$	$4 - 3 = 1$	$A X_{3} E$	trigonal pyramidal
(c) $H_{2} O$	$\frac{2 + 6}{2} = 4$	2	$4 - 0 = 4$	$4 - 2 = 2$	$A X_{2} E_{2}$	angular
(d) $C l O_{3}^{-}$	$\frac{7 + 18 + 1}{2} = 13$	3	$13 - 9 = 4$	$4 - 3 = 1$	$A X_{3} E$	Pyramidal
(e) $I C l_{4}^{-}$	$\frac{7 + 28 + 1}{2} = 18$	4	$18 - 12 = 6$	$6 - 4 = 2$	$A X_{4} E_{2}$	Square planar