Vsper

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CONTENTS:
Introduction
Postulates of VSEPR Theory
Generic formula of AB
Generic formula of AB3E
Generic formula of AB4E2
Limitations
Conclusion
Reference

2.  INTRODUCTION
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VSEPR [Valence shell electron pair repulsion]
This theory is developed by RONALD GILLESPIE and RONALD
NYHOLM in the year 1957.
This theory is also called GILLESPIE-NYHOLM theory.
The main idea of VSEPR that is “pairs of electrons in bond pair
and in lone pair repel each other”.
Thus far, we have used two dimentional lewis structure to
represent molecule. However molecular structure is actually
three-dimensional.

3. POSTULATES OF VSEPR THEORY
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The central metal atom is surrounded by only bond pair not lone pair,
hence the molecule have REGULER GEOMETRY.
When both the bond pair and lone pair present on central metal
atom, the molecule will have IRREGULER OR DISTORTED GEOMETRY.
One pair of electron in valence shell repel another pair of electron
because they are electro negative.
Triple bond have more repulsion than double bond similarly double
bond have more repulsion than single bond.
The lone pair takes more space around a central atom than a bond
pair.
This theory is used to predict the molecular shapes of various
molecular from the electron pairs that surrounded the central atom
of the molecule

4. Total
domain
s
Electron
Geometry
Generic
formula
Bonde
d Pairs
Lone
Pairs
Molecular Shape Exemple
1 Linear AB 1 0 Linear H2
2 Linear
AB2
ABE
2
1
0
1
Linear
CO2
CN
3
Trigonal
Planar
AB2E
ABE2
AB3
2
1
3
1
2
0
Bent
Linear
Trigonal Planar
O3
O2
BF3
4
Tetrahedr
al
AB4
AB3E
AB2E2
ABE3
4
3
2
1
0
1
2
3
Tetrahedral
Trigonal
Pyramidal
Bent
Linear
CH4
NH3
H2O
Cl2

5. 5
Trigonal
Bipyramid
al
AB5
AB4E
AB3E2
AB2E3
5
4
3
2
0
1
2
3
Trigonal
Bipyramidal
See saw
T shape
Linear
PF5
HF4
CF3
I3
6
Octahedra
l
AB6
AB5E
AB4E2
6
5
4
0
1
2
Octahedral
Square
Pyramidal Square
SF6
IF4
XeF4

6. GENERIC FORMULA – AB
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A – The Central atom
B – An atom bonded to A
Ex: H2
It contains one bond pair and zero lone pair.
Dihydrogen is an element molecule consisting of the two
hydrogen joined by a single bond.
Two hydrogen atoms are bonded together.
It is axial overlap.
It forms linear structure.
The bond angle is 1800.
H H

7. GENERIC FORMULA - AB3E
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A-The central atom
B-An atom bonded to A
E-A lone pair on A
Ex:NH3
It contains three bond pair and one lone pair.
Outermost shell contains 8 electron i.e 4 electron pair in that 3
bond pair and 1 lone pair.
Four electron pairs raise to tetrahedral structure and in this case
three positions is occupied by H atoms and fourth position is
occupied by lone pair of electron.

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Presence of lone pair causes
slight distortion from bond angle
of 109.50 to 107.50.
The electron geometry of NH3 is
tetrahedral where as molecular
geometry is trigonal pyramidal.

9.  GENERIC FORMULA – AB4E2
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Ex:- XeF4
Here the central metal atom is Xe,
and it is surrounded by four F
atoms and two pairs of lone pair
electron.
XeF4 contains 6 electron pairs,
means 12 electrons in that 4
electron pairs are bond pair and
the other 4 electron i.e 2 lone pair.
The electron geometry of XeF4 is
octahedral but due to presence of
two lone pair electron the
molecular geometry is square
planar.
The bond angle is 900 or 1800

10.  LIMITATIONS
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This theory can’t explain the structure of the
transition metals compounds and ions.
This theory can’t be used to obtain the exact
bond angles between the atoms in a molecule.
Halides of group two elements should have a
linear structure according to this theory, but
their actual structure is a bent one.

11. CONCLUSION:-
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VSEPR Theory can be used to predict the
shapes of molecule.
The molecular shape gives the arrangement
of atoms in a molecule.
The electron pair geometry gives the
arrangement of bonding and non-bonding
pairs around a central atom.