# What are lone pairs and how are they represented in a Lewis dot diagram?

Jun 23, 2018

These are conceived to be pairs of electrons present on the central atom, that DO NOT participate in bonding....

#### Explanation:

And ammonia is a go to example....

For nitrogen, $Z = 7$, and thus there are 7 electrons, of which TWO are inner core, and not conceived to participate in intermolecular bonding....and FORMALLY there are 3 nitrogen based electrons in EACH of the $N - H$...the other electron that constitutes the bond derives from hydrogen....

And so we gots…$\ddot{N} {H}_{3}$...and now the LONE PAIR is stereochemically active..electronic geometry is tetrahedral, and molecular geometry is trigonal pyramidal. And because the non-bonding nitrogen lone pair lies fairly close to nitrogen it compresses the $\angle H - N - H$ bond down from ${109.5}^{\circ}$ to approx. ${105}^{\circ}$ in ammonia.

On other hand, the lone pair explains the basicity of the ammonia molecule. Ammonium ion, $N {H}_{4}^{+}$, is a REGULAR tetrahedron.

And they are normally represented by a double-dot...alternatively we could try to draw the $s {p}_{3}$ hybrid orbital...

Note that ammonia is a rather potent donor, and as well as binding to a proton ${H}^{+}$, it could bind to transition metal centres to give ammonia complexes....

Ammonium ion is more or less a regular tetrahedron...with $\angle H - N - H = {109.5}^{\circ}$,,