This document discusses valence shell electron pair repulsion (VSEPR) theory, which is used to predict the shape of covalent molecules and polyatomic ions based on the arrangement of electron pairs around the central atom. According to VSEPR theory, electron pairs around the central atom repel each other and arrange themselves as far apart as possible to minimize repulsion. The type of electron pair repulsion determines the molecular shape, with lone pairs repelling each other more than lone pairs and bonding pairs or just bonding pairs alone. Examples are provided to illustrate VSEPR theory predictions of molecular geometry.

1. Molecules and Molecular Structure
Valence Shell Electron Repulsion Theory
(VSEPR)
Sharifah Mona Abdul Aziz Abdullah
Abdul Al-Hafiz Ismail
Centre for Pre-University Studies
Universiti Malaysia Sarawak
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2. Introduction
The covalent bonds have directions in space,
which can give rise to different molecular
shapes.
Lewis structure shows the number of bonding
but can not be used to predict the molecular
shape.

3. VSEPR Theory
VSEPR theory is used to predict the shape for
covalent molecules and polyatomic ions.
The shape of a molecule or ion is governed by
the arrangement of the electron-pairs (bond
and lone pairs) around the central atom.

4. VSEPR Theory
According to VSEPR theory:
a) The electron-pairs around the central atom will
repel one another.
b) The electron-pairs (bond and lone pairs) arrange
themselves to be as far apart as possible in the
valence shell to minimise the force of repulsion.

5. VSEPR Theory
The order of repulsion between electron pairs is:
• 2 lone pairs will repel each other the most (leading to a
wider bond angle).
• A lone pair and a bond pair will repel each other less
(smaller bond angle than for 2 lone pairs).
• 2 bond pairs will repel each other much less (smallest
bond angle).
lone pair-lone pair > lone pair-bonding pair > bonding pair-bonding pair

6. The molecule below shows a repulsion between
electron pairs (bonding pair-bonding pair):
VSEPR Theory
F
F
F
BF F
H
H
H
C
H
Be
Beryllium fluoride
2 bond pairs
Bond angle: 180°
Shape: Linear
Boron triflouride
3 bond pairs
Bond angle: 120°
Shape: Trigonal planar
Methane
4 bond pairs
Bond angle: 104.5°
Shape: Tetrahedral

7. The molecule below shows a repulsion between
electron pairs (lone pair-bonding pair and lone
pair-lone pair):
VSEPR Theory
H H
N
H H
H
O
Ammonia
3 bond pairs, 1 lone pair
Bond angle: 107°
Shape:Trigonal bypyramidal
Water
2 bond pairs,2 lone pairs
Bond angle: 104.5°
Shape: V-shape