Linear Shape
- BeH2
- 180°
- 2 bonding pairs
Trigonal Planar
- BF3
- 120°
- 3 bonding pairs
Tetrahedral
- CH4
- 109.5°
- 4 bonding pairs
V-Shaped
- H2O
- 104.5º
- 2 bonding pairs and 2 lone pairs
Pyramidal
- NH3
- 107º
- 3 bonding pairs and 1 lone pair
Electron Pair Repulsion Theory the electron pairs in the outer shell of the central atom repela each other and end up as far apart as is geometrically possible
Since lone pairs are closer to the nucleus of the central atom, they are closer together, so their mutual repulsion is greater than that between bond pairs >>>> distorted shape
Order of Strength of Repulsions
- lone pair:lone pair
- lone pair:bond pair
- bond pair: bond pair
Symmetry and Polarity
Symmetrical Atoms
- Linear
- Tetrahedral
- Trigonal Planar
- Non- polar (even if bonds are polar)
E.g. BF3
Boron (central atom) is slightly positive >>> centre of positive charge is here
Each flourine is slightly negative >>> centre of positive charge is the central point between these atoms
Centre of positive coincides with centre of negative >>> non-polar
Non-Symmetrical Atoms
- V-Shaped
- Pyramidal
- Polar
E.g. NH3
Nitrogen (central atom) is slightly negative >>> centre of negative charge will be at apex of pyramid
Hydrogen atoms areslightly positive >>> centre of positive charge at base of pyramid
Centre of negative does not coincide with centre of positive >>> polar
