Question

How can I determine molecular geometry?

Answer 1

VESPR stands for valence shell electron pair repulsion. This theory basically says that bonding and non-bonding electron pairs of the central atom in a molecule will repel (push away from) each other in three dimensional space and this gives the molecules their shape.

We can use the following notations when examining a Lewis structure of a molecule.
A = central atom
X = peripheral atoms
E = non-bonding electron pairs of the central atom

`AX_2` = linear molecule (example `CO_2`)
`AX_3` = trigonal planar (example `AlH_3`)
`AX_3E` = trigonal pyrimidal (ex. `NH_3`)
`AX_2E_2` = bent (ex. `H_2O`)
`AX_4` = tetrahedral molecule (ex `CH_4`)