The Valence Shell Electron Pair Repulsion (VSEPR) Model:
The electrons repel each other in covalent bonds and they try to stay as far apart as possible, which results in angles and weird 3D structures.
All of the following count as ONE domain and are equal.
And they are counted as the ones that are ON the CENTRAL atom
- Lone pairs
- Single bond
- Double bond
- Triple bond
Linear (2 domains): 180
Trigonal Planar (3 domains): 120
Tetrahedral (4 domains): 109.5 (not planar)
Trigonal Bipyramidal (5 domains): 3*120 AND 2*180, but kinda 90 compared to other atoms
Octahedral (6 domains): 4*90 AND 2*180, but kinda 90 compared to other atoms
Equatorial pairs/bonds: The horizontal bonds for trigonal bipyramidal.
Axial pairs/bonds: The Vertical bonds for trigonal bipyramidal.
IF there are NO lone pairs on the central atom, then the molecular geometry is the SAME as the electronic geometry.
IF not then the VSEPR structure will be different, as lone pairs have more repulsion and aren’t atoms.
Strengths of Repulsion Order:
This means that the angle is going to decrease, as bonding pairs are there.
- Lone pair TO lone pair
- Lone pair TO bonding pair
- Bonding pair TO bonding pair
For H2O, the angle between H and H is smaller than the angle between the two lone pairs on O.