Question

Does a lone pair count as a sigma bond?

Answer 1

Lone pairs of electrons are found in nonbonding orbitals, i.e. they are not being used to bond. Therefore, they do not count as `sigma`-bonding pairs.

Lone pairs of electrons are within a defined orbital space, but mostly what they do is take up space, repelling the bonding pairs of any nearby flexible bonds and changing bond angles.

That's why water has a smaller `"H"-"O"-"H"` angle (`104.4776^@`) than the `"H"-"N"-"H"` angle of ammonia (`106.67^@`), and why ammonia has a smaller `"H"-"N"-"H"` angle than the `"H"-"C"-"H"` angle of methane (`109.471^@`).

Try drawing out their lewis structures and notice how many lone pairs each one has.

You can look up the bond angles here:
http://cccbdb.nist.gov/exp1.asp