1. Shapes of Covalent Molecules

2. VSEPR Theory
VSEPR stands for Valence shell electron pair repulsion theory
It describes how the shape of a molecule is determined by the number of pairs of electrons in the outer shell of the central atom in a bond
The electrons will always arrange themselves to be as far apart as possible as the negative charges repel eachother

3. The Shapes of covalent Molecules

4. Linear
A Linear molecule 180° between atoms this will form when there are 2 pairs of electrons around the central atom

5. Trigonal Planar
A Trigonal Planar molecule will occur if there are 3 pairs of electrons around the central atom the electrons are 120° apart

6. Tetrahedral
A tetrahedral molecule will occur if there are 4 bond pairs around the central atom
The electrons are 109.5° apart

7. Exceptions
In all the examples we have seen there are no lone pairs of electrons in the outer shell of the central atom
If there are lone pairs they will have a stronger force of repulsion and will change the shape of a molecule
An example is seen in ammonia NH3

8. The lone pair of electrons (ie those not involved in a bond) have a strong force of repulsion and cause the shape of the molecule to change

9. Pyramidal molecules Ammonia is an example of a pyramidal molecule
This shape occurs if there are 3 bond pairs and 1 lone pair of electrons around the central atom
The bond angle is 107°

10. V shaped molecules
If there are 2 lone pairs and 2 bond pairs around the central atom a v shaped molecule ocurrs
The bond angle
in this case is
104.5°

11. A table to help you remember
Total number of electron pairs
Number of bond pairs
Number of lone pairs
Shape of molecule
Examples 2
Linear 3
Trigonal planar 4
Tetrahed-ral 1
Pyramid-al
V-shaped

12. Try to use VSEPR theory to deduce the shape of the following molecules
BeH2
SiCl4
PBr3
CH4
H2O
AlH3