Does a lone pair count as a sigma bond?

1 Answer
Truong-Son N.
Feb 15, 2016

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

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