# How do you know what the maximum bond angle is for a molecule?

Aug 1, 2017

Well, the "maximum" bond angle is the VSEPR-predicted bond angle, i.e. the ideal bond angle that minimizes electron repulsions and distributes atoms evenly in space (whatever "evenly" means), and you can find that in your textbook. We generally talk about deviations from ideal bond angles as contractions.

An example using tetrahedral electron geometry is shown here, and we obtained ${109.5}^{\circ}$ for, e.g. ${\text{CH}}_{4}$, ${\text{CCl}}_{4}$, etc.

There is no higher bond angle than that for tetrahedral electron geometries, unless one identifies the bond angle from the wrong side of the molecule...

(i.e. if one looked at water,

whose bond angle is ${104.4776}^{\circ}$, that is the acute angle, and we do not care about the ${255.5224}^{\circ}$ obtuse angle. The contraction from ${109.5}^{\circ}$ is due to the lone pair of electrons on the oxygen atom, repelling against the bonding-electron pairs to crunch the molecule together by ${5.0224}^{\circ}$.)