A Critique of the Proposed National Education Policy Reform
Vsepr theory
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.
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.
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′
20.
21.
22.
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