= Ammonia molecular orbital diagram
In pyramidal <ammonia>, the hydrogen <symmetry orbitals> span $A_1\oplus E$ of the <C3v molecular point group>. Nitrogen $2s$ and $2p_z$ both have $A_1$ symmetry and $(2p_x,2p_y)$ span $E$. In the planar <D3h molecular point group>, these become $A_1'$, $A_2''$ and $E'$, respectively, while the hydrogen combinations span $A_1'\oplus E'$. Thus the planar out-of-plane <lone pair> is a symmetry-isolated <nonbonding orbital>; pyramidalization permits mixing with the other $a_1$ functions.<Explaining the geometry of simple molecules using molecular orbital energy-level diagrams built by using symmetry principles by Sérgio P. Machado and Roberto B. Faria>[The ammonia molecule, Figures 7–9 and Tables 4–5: orbital symmetries in both geometries]{ref}
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