When do bond angles deviate

Ideal bond angles are determined by ideal geometry. However, when some molecule geometries are evaluated experimentally, the bond angles deviate from the ideal angles. Usually, deviation of bond angles occurs in molecules with lone pairs on the central atom.

Lone pair electrons spread out more than bonding electrons. This is because bonding electrons are confined to the space between two atoms. The lone pairs are therefor larger and can push the bonding pair electrons closer together. This causes a decrease in the bond angle compared to the ideal angle. Water molecules are a great example of bond angle deviation. It was something along the lines of that bond angles can be rationalized using vdW repulsions alone. I suspect your prof may have wanted to avoid getting into certain gray areas which are numerous in chemistry ; I've certainly seen this plenty of times with my own profs.

Steric effects which is kind of a catch-all term mostly referring to Pauli electron-electron repulsion are certainly quite dominant in many cases, especially in simple and highly symmetrical structures, but they're not the whole story. Show 1 more comment. Active Oldest Votes. Electronegativity: If the electronegativity of the central atom decreases, bond angle decreases. Good Side note: Triple bonds repel other bonding-electrons more strongly than double bonds. Improve this answer. Being a concept, hybridization has nothing to do with the actual energetics of why a molecule adopts a certain geometry.

In fact, there are many cases were hybridization fails to explain reality, the water molecule being a case in point. But what it allows us is classification. It allows us to associate particular arrangements with particular geometries. And with Chemistry, there are a ton of exceptions, so it's definitely not perfect. But when thinking about bond angles its helpful to associate like things so we can see patterns.

And by Repel, I mean simply to push away, as in more often a more significant change in bond angle. Not only is hybridisation, in this way of using it, a man-made concept of purely mathematical considerations - it is also always only the result of a geometrical arrangement of atoms in a molecule.

And as this is true, it can only be applied to molecules composed out of the first and second period. Apart from the obvious water example ron already mentioned. This exercise will also give students practice in drawing lewis structures because they will need to decide if a multiple bond is present before they can correctly explain why the molecule does conform to ideal geometry.

Variations From Ideal Geometry Many factors lead to variations from the ideal bond angles of a molecular shape. Suggested activity 1: If students did activity 1 in the "VSEPR" topic, they will have already noticed that although there are specific angles that create an ideal tetrahedron or trigonal planar molecule, molecules of those shapes don't often possess angles of exactly The lone pair occupies more space around the central nucleus than a bond would because the orbital is not stretched between two nuclei as it would be in a bond.