Vsepr Theory Notes
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Vsepr Theory Notes
Jul 25, 2022, 16:45 IST
VSEPR THEORY
For molecules that contain only single bonds.
This theory is known as valence shell electron pair repulsion theory, which determines the shape and molecular geometry in a polyatomic molecule. There is a central atom, which is surrounded by bonded electron pairs or lone pairs of electron and shared pair of electrons in its valence shell. These electron pairs extend a repulsion force on one another and so lie as far apart from one another as possible so that the force of repulsions are minimized. The repulsive forces between various types of electron pairs are in the order
lp-lp > lp-bp > bp-bp
Thus the Molecular geometry is determined by the number and nature of pairs of electrons surrounding the central atom. If there are only bond pairs in the valence shell around the central atom it has regular geometry; but when there are lone pairs also in the valence shell, the geometry becomes irregular due to increase in force of repulsion. Geometry corresponding to number of bond pairs and lone pairs are given in the following table.
Table of valence shell electron pair repulsion theory VSEPR
Shape of Molecules/Ions having only bond Pairs of Electrons
|
No.of bp of electrons at
the central atom |
Hybridization | Bond angle | Shape of molecule | Examples |
| 2. | Sp | 180° | Linear |
BeX
2
,CO
2
,HgCl
2
,ZnCl
2
,HCN,
MgCl 2 ,C 2 H 2 (alkynes) (X=F,Cl,Br,l) |
| 3. | Sp2 | 120° | Trigonal Plana r |
BF
3
,BCl
3
,BBr
3
,BH
3
,AlCl
3
,SO
3
,C
2
H
4
AlCl 3 ,SO 3 ,C 2 H 4 |
| 4. | Sp3 | 109.5° | Tetrahedral |
(alkanes),NO
2-
3
,C
6
H
6
SiX 4 ,SnCl 3 ,CH 4 ,(alkanes),CX 4 SO 2- 4 ,ClO - 4 ,NH + 4 ,BF - 4 |
| 5. | Sp3d | 90° 120° | Trigonal bipyramidal |
PCl
5
,PF
5
SbCl
5
SF 6 ,SeF 6 ,TeF 6 |
