Do double and triple bonds count as one region of electron density?

Yes, in IB Chemistry VSEPR counting, a single bond, double bond, and triple bond each count as one electron domain. That’s because the electron density is still located between the same two atoms, so it acts like one “cloud” in terms of spatial arrangement. However, it’s helpful to remember that multiple bonds contain more electron density within that one domain. This can increase repulsion slightly and cause small angle distortions in real molecules. On exams, the safe method is: count it as one domain first, then mention “slightly greater repulsion” only if the question asks about deviations from ideal angles. Practise a few examples and you’ll start spotting when the examiner wants that extra sentence.

Why do lone pairs repel more strongly than bonding pairs?

Lone pairs are attracted to only one nucleus, so their electron density stays closer to the central atom. In IB Chemistry language, that usually means they occupy more space in the valence shell and create stronger repulsive effects. Bonding pairs are shared between two nuclei, so their density is pulled outward and feels less “bulky” near the central atom. This difference matters because VSEPR is really an energy story: lower energy comes from less repulsion. When lone pairs are present, they push bonding pairs closer together, compressing bond angles. That’s the logic behind 109.5° in CH₄, smaller angles in NH₃, and even smaller in H₂O. If you write that chain clearly, you usually earn full marks.

Does electron pair repulsion explain polarity too?

Electron pair repulsion explains shape, and shape is one of the two ingredients of polarity (the other is electronegativity differences). In IB Chemistry, you often first predict the 3D geometry using VSEPR. Then you consider bond dipoles and whether they cancel due to symmetry. For example, CO₂ is linear and symmetrical, so dipoles cancel and the molecule is non-polar. H₂O is bent, so dipoles don’t cancel and the molecule is polar. So VSEPR doesn’t directly “create” polarity, but it sets the stage for it. If your shape is wrong, your polarity conclusion will usually be wrong too. That’s why VSEPR is a high-leverage topic.

This site uses cookie tracking technologies. Learn more in our Cookie Policy.

IB Chemistry: Why Electron Pair Repulsion Sets Shape

IB Chemistry

RevisionDojo Team

•12/8/2025•6 min read

Molecules don’t “choose” to be bent or tetrahedral because they like aesthetics. They do it because electrons hate being crowded.

In IB Chemistry, this is one of those ideas that feels almost too simple at first: negative charges repel, so electron pairs spread out. But that simple push-away instinct becomes a reliable prediction tool on exam day. Once you see molecular shape as an energy-saving decision, VSEPR stops being memorisation and starts being logic.

The core idea: electron pairs maximise distance

VSEPR (Valence Shell Electron Pair Repulsion) theory says regions of electron density around a central atom arrange themselves as far apart as possible to minimise repulsion and lower energy. In IB Chemistry, these “regions” are often called electron domains, and they include: