1. Valence Shell Electron Pair
Repulsion Theory
M.SARAVANAKUMAR
M.TECH –I YEAR
Centre for Nanoscience and Technology,
Pondicherry University
11/9/2012

2. INTRODUCTION
• VSEPR Theory was suggested by Sidgwick and
Powel[1940]
• It was developed by Gilllespe and Nyholm in
1957.
• Based on that in a polyatomic molecule the
direction bonds around the central atom
depends on the total number of Bonding
&Non-bonding electron pairs in its valance
shell.

3. VSEPR Theory
• The shape of the molecule is determined by
repulsions between all of the electron present in the
valance shell.
• Electron pairs in the valence shell of the central
atom repel each other and align themselves to
minimize this repulsion.
• Lone pair electrons takes up more space round the
central atom than a bondpair.
• Lone pair attracted to one nucleus, but bond pair is
shared by two nuclei.
• The minimum repulsions to the state minimum
energy and maximum stability of the molecule.

4. Repulsion strengths
• Lone pair -Lone pair  Lone pair
-Bond pair  Bond pair-Bond pair

5. Repulsion strengths
Triple bond >double bond >single bond

6. • Presence of lone pairs on the central atom causes
slight distortion of the bond angles from the ideal
shape.
• The magnitude of repulsions between bonding pairs
of electrons depends on the electronegativity
difference between the central atom &the other
atoms .

7. Steps in the prediction of geometry
• Determine the central atom.
• Draw the electron dot structure and bar diagram
• Find arrangement of electron pairs.
• Find arrangement of bonding pairs.
• Determine the geometry based on of bonding pairs.

8. SHAPES OF MOLECULES CONTAINING
BONDED PAIRS OF ELECTRONS ONLY

9. Central atom with Two Electron Pairs
There are two electron pairs in the valance shell
of Beryllium. [1s2 2s2 ]
Molecular geometry-Linear arrangement
H Be H

10. Central atom with Three Electron Pairs
Trigonal Planar
Three electron pairs in the valance shell of
Boron. [1s2 2s2 2p1 ]
Molecular geometry- Trigonal Planar
arrangement
F
B
F F

11. Central atom with Four Electron Pairs
Tetrahedral
Four electron pairs in the valance shell of
Carbon. [1s2 2s2 2p2 ]
Molecular geometry- Tetrahedral
Bond angle -109.5:

12. Central atom with Five Electron Pairs
Five electrons in the valance shell of
Phosphorus. [1s2 2s2 2p6 3s2 3p3 ]
Molecular geometry- Trigonalbipyramid
Bond angle -120: &90:

13. Central atom with Six Electron Pairs
Six electrons in the valance shell of
Sulphur. [1s2 2s2 2p6 3s2 3p4 ]
Molecular geometry- Octahetral
Bond angle-90:

14. SHAPES OF MOLECULES CONTAINING
BONDED PAIRS AS WELL AS LONE PAIRS
OF ELECTRONS

15. Central atom with Four Electron Pairs
Tetrahedral
Five electrons in the valance shell of
Nitrogen. [1s2 2s2 2p3]
Molecular geometry- Tetrahedral
Electron pairarrangement - Trigonal Pyramidal
Presence of lonepair causes slight distortion from
109:28′ to 107:48′

16. Central atom with Four Electron Pairs
Tetrahedral
Six electrons in the valance shell of Oxygen atom.
[1s2 2s2 2p4 ]
Molecular geometry- V-Shaped or Bent shape
Electron pairarrangement- Tetrahetral
Repulsions between Lonepair- Lonepair ,
Lonepair -Bondpair is possible.
It causes slight distortion from 109:28′ to 104:27′

17. Central atom with Five Electron Pairs
Five electrons in the valance shell of
Sulphur. [1s2 2s2 2p6 3s2 3p4 ]
Molecular geometry- seesaw[or distorted octahedron]
Electron pair arrangement- Trigonalbipyramidal
Lonepair –bondpair repulsion

18. Central atom with Six Electron Pairs
Seven electrons in the valance shell of
xenon : 1s2 2s2 2p6 3s2 3p6 3d104s2 4p6 4d10 5s2 5p6
Molecular geometry- square planar
Electron pairarrangement- octahedral
Lonepair –bondpair repulsion

19. EFFCT OF ELECTRONEGATIVITY
Five electrons in the valance shell of
Nitrogen. [1s2 2s2 2p3]
Molecular geometry- Tetrahedral [e-pairs arrangement]
orTrigonal Pyramidal[VSEPR]
Presence of lonepair causes slight distortion from 109:28′ to
107:48′to102:30′
Repulsion between bonpair-bondpair is less in NF3 than inNH3
102:30′

23. Limitations of VSEPR
• It fails to predict the shapes of isoelectronic
species[CH4&NH4+] and transition metal
compounds.
• This model does not take relative sizes of
substituents .
• Unable to explain atomic orbitals overlap.

24. Seven electrons in the valance shell of
xenon : 1s2 2s2 2p6 3s2 3p6 3d104s2 4p6 4d10 5s2 5p6
Molecular geometry-
Pentagonalbipyramid[VSEPR], DistortedOctahedral[actu
al]
Lonepair –bondpair repulsion

25. REFERENCES
• Concise Inorganic chemistry-J.D.LEE[Fifth
edition]-Black well publishing.
• Chemistry-Raymond chang.
• Pictures from Wikipedia- free encyclopedia-
www. Wikipedia.org.
• Pictures from Google Images.
Thanks to my Teachers & friends

26. THANK YOU