Bond Angles

(Polar molecules, Non-polar molecules, etc.)

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Bond Angles

Postby 004643111 » Mon Oct 26, 2015 1:12 pm

Bonding angles for linear, trigonal planar, tetrahedral, and octahedral typically have 180, 120, 109.5, and 90 degree angles, respectively. Are there any exceptions to this? For example, will lone pairs have an effect on the angle measures as opposed to paired electrons?

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Re: Bond Angles

Postby Chem_Mod » Mon Oct 26, 2015 1:44 pm

Hello Maria,

Good question, if you look at page 80 of your course reader, you will see that the strength of repulsion is listed as: lone-lone pair>lone-bonding pair>bonding-bonding pair. As an example consider methane (CH4) and the sulfite ion (SO3 2-). Methane is tetrahedral in shape and has 4 equivalent bond angles of 109.5 DEG. The sulfite ion has 3 zones of electron density (3 bonding pairs and 1 lone pair), because of the lone pair, the bond angles are not the expected 109.5 DEG, they are in fact 106 DEG, which is a smaller value. This is because of the greater repulsion between lone-bonding pairs.

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