VSEPR theory with postulates and shapes

1. VSEPR THEORY AND
MOLECULAR GEOMETRIES
Presented by
SHUMAILA MUNAWAR

2. VSEPR Theory
Valence shell electron pair repulsion theory
Valence electrons(e pair) are of 2 types
1.Lone pair ..
2.Bond pair -
Electron pair determine the shape of molecules
Shapes of molecules
given by sidgwick and powell
1940

3. Principle
Pairs of electrons would repel each other and
take up positions so as to remain as far apart as
possible.
Lone pair-lone pair ≥ lone pair-Bond pair ≥ bond pair-bond pair
.. .. ≥ .. - ≥ - -
Electrons pairs should be at maximium distance so
repulsion between them minimum

4. Postulates
1) The arrangement of electron pair in the
valenece shelll is that which makes them to
remain at maximum distance apart.
2) Lone pair occupy more space than bonding pair.
Lone pair under the influence of 1 nuclues
Bonding pair is under the influence of 2 nuclei.
Y X Y

5. 1) The influence of bonding electron pair decrease
with increasing value of electronegtivity.
2) The 2 electrons pair of a double bond = or 3
electron pair of triple bonds ≡ takes more
position than 1 electron pair of single bond -.

6. AB2
AB3
AB4
AB5
AB6

7. Applications of VSEPR theory
AB2 Type
 In case of 2 e pair the
possible shape to
remain them at
maximum distance is
to arrange them at
angle of 180.
 This will give linear
shape
2 means 2 electrons pair
that mightbe lone pair or
bond pair

8. Shape Linear
AB2 type

9. AB3 Type
3 bond pair 2 bond pair 1 lone pair
v shaped
triangular plane

10. 3 bond pair
triangular
2 bond pair
1 lone pair
Here greater repultion takes place that why distortion of shape takes place
so v shaped

11. AB4 Type
4 bond pair 3 bond pair 1 lone pair
Trigonal pyramidTetrahedral
2 bond pair 2 lone pair
V shaped

12. CH4 NH3
 4 bond pair
 Angle is 109.5
 shape tetrahedral
 3 bond pair 1 lone pair
 Angle is 107
 shape trigonal pyramidal
In case of NH3 lone pair is also present so greater repultion takes placethat will
distort the shape
H2O
 2 bond pair 2 lone pair
 Angle is 104.5
 bent or V shape
In case of water 2 lone pairs are present so more and more repulsion
distotort the shape

13. Due to lone pair ,bond pair
and bond pair bond pair
repulsion angle distorted
Due to lone pair ,bond pair
bond pair bond pair and
lone pair lone pair
repulsion angle distorted more
3 Types of replusion
takes place in H2O

14. AB5 Type
5 bond pair 4 bond pair
1 lone pair
Irregular
Tetrahedorn
Trigonal
bipyramidal
3 bond pair
2 lone pair
T shaped
2 bond pair
3 lone pair
Linear

15. 5 Bond pairs present
trigonal bipyramidal
Due to 1 lone pair ,
repulsion takes place
angle and shape distorted
irregular terahedron
Due to 2 lone pair greater
repulsion angle and shape
distorted
T shaped
5 lone pairs so greater
repulsion takes place
shape and angle
distorted Linear shape

16. AB6 Type
6 bond pair
5 bond pair
1 lone pair
Square
pyramid
Octahedral
shape
4 bond pair
2 lone pair
Square
planar

17. 6 Bond pairs present
Octahedral shape
5 Bond pairs present1 lone pair
due to repulsion shape distorted
Square pyramid
4 Bond pairs and 2 lone
pair present due to repulsion
shape distorted
Square planer

18. AB7 Type
7 bond pair
6 bond pair
1 lone pair
Irregular
octahedron
Pentagonal
bipyramidal