Geometry of molecule
- It is the relative arrangement of bonded atoms in a molecule.
- The way in which the bonded atoms direct themselves around the central atom is explained on the basis of this theory.
- This theory was given by Sid wick and Favell.
- In this only the valence electrons participate in bond formation.
- The bonded atoms around central metal atom will have repulsions between them
- Therefore, they will arrange themselves in such way that the repulsion is minimum.
In BF3 the arrangement is like it is shown below:
To minimize the repulsion, the fluorine directs them around boron in such a way as shown above in figure.
Postulates of VSEPR theory
The basic idea behind it is that the bonded atoms in a molecule adopt the particular arrangement in space around the central metal atom which keeps them as far as possible.
- The shape of molecule depends upon the number of valence shell electron pairs.
- Bonded electrons = participate
- Lone pair = do not participate
- The electron pairs occupy the positions such as to minimize repulsions
- The valence shell is taken as sphere in which the surrounding atoms takes places as far as possible from each other.
- The repulsions are between bond pair –bond pair, lone pair –lone pair and also bond pair –lone pair.
- The magnitude is: L.P-L. P>L, P-B. P>B.P-B. P
- The repulsive forces decrease as distance between bonded atoms increase therefore bond angle increases.