# What is molecular geometry?

Molecular geometry is a way of describing the shapes of molecules. It applies a theory called VESPR for short.

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

$A {X}_{2}$ = linear molecule
$A {X}_{3}$ = trigonal planar
$A {X}_{3} E$ = trigonal pyrimidal
$A {X}_{2} {E}_{2}$ = bent
$A {X}_{4}$ = tetrahedral molecule

Here are some examples:

${H}_{2} O$ we need to consider the central atom of water which is oxygen. The oxygen has two bonding electron pairs (single bond to each H) and two non-bonding pairs giving water a $A {X}_{2} {E}_{2}$ conformation and a bent shape.

$C {O}_{2}$ is $A {X}_{2}$ = linear molecule
$B {H}_{3}$ is $A {X}_{3}$ = trigonal planar
$N {H}_{3}$ is $A {X}_{3} E$ = trigonal pyrimidal
$C {H}_{4}$ is $A {X}_{4}$ = tetrahedral molecule