Question

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

Answer 1

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…`ddotNH_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 `/_H-N-H` bond down from `109.5^@` to approx. `105^@` in ammonia.

On other hand, the lone pair explains the basicity of the ammonia molecule. Ammonium ion, `NH_4^+`, is a REGULAR tetrahedron.

And they are normally represented by a double-dot...alternatively we could try to draw the `sp_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 `/_H-N-H=109.5^@`,,