# What is the orbital overlap diagram for "NH"_3?

Feb 12, 2016

The atomic orbital of $\text{H}$ that is both compatible and close enough in energy with the $n = 2$ atomic orbitals of $\text{N}$ is the $1 s$.

The $1 s$ atomic orbital of $\text{H}$, with $E = - \text{13.6 eV}$, is close enough in energy (less than $\text{12 eV}$ away) to the $2 p$ atomic orbitals of $\text{N}$, with $E = - \text{13.1 eV}$, that it can overlap with SOME of them.

In a nonlinear molecule, the $2 {p}_{y}$ orbitals of nitrogen line up directly (head-on, colinear) with hydrogen---the $y$ direction of the $\text{N"-"H}$ bond is along the bond. The $z$ direction is through the tip of the trigonal pyramid.

The MO diagram for ${\text{NH}}_{3}$ is:

[Do note though that this diagram has a typo; the $1 s$ atomic orbital of nitrogen should be a $2 s$.]

As you can see, the $2 p$ atomic orbitals of $\text{N}$ are indeed very close in energy with the hydrogen $1 s$ atomic orbitals.

The nonbonding orbital holding the lone pair is the $3 {a}_{1}$, which ends up being contributed to mostly by the $2 {p}_{z}$ of $\text{N}$ and slightly by the $1 s$ orbitals of the three $\text{H}$ atoms as a group.

So, the "orbital overlap" diagram would look something like this: