Molecular Geometry and VSEPR

VSEPR stands for Valence Shell Electron Pair Repulsion. Bonding electrons are (mostly) shared in the space between the two atoms in the bond. When multiple bonds are connected to a single atom the bonding pairs repel each other. The electrons try to position themselves as far from each other as possible. We must remember that molecules are 3-dimensional shapes and hence have a Molecular Geometry that looks different from the 2D Lewis diagrams.

Non-bonding (lone pair) electrons also repel bonding electrons and therefore must be taken into account when considering electron geometry. However, these electrons are often not represented in molecular shape diagrams. Additionally, lone pair electrons have a stronger repulsion than bonding electrons and push bonding pair electrons together more thereby reducing bond angles.

Remember that electrons in an energy shell are not all in the same place. They exist in differently shaped orbitals.

Because different orbitals have different shapes, we might expect that bonds made between different types of orbitals would have a different shape or bond length. However this is not what scientists observe.

Let's take a look electron configuration in carbon making 4 bonds:

Carbon has electrons in the 2s orbital and three 2p orbitals. S and P orbitals are not the same shape. However, all 4 bonds are exactly the same. How does carbon do this?

When atoms share electrons the orbitals that those electrons inhabit overlap.