Question 1

How does VSEPR theory handle molecules with double or triple bonds, like carbon dioxide (CO₂)?

Accepted Answer

For the purpose of determining molecular shape, a double or triple bond is treated as a single region of electron density, sometimes called an 'electron domain'. In CO₂, the central carbon atom has two double bonds (O=C=O). We count this as two electron domains. Two domains will arrange themselves linearly to be as far apart as possible, resulting in a 180° bond angle and a linear molecule.

Question 2

Why do we focus only on the valence electrons of the central atom?

Accepted Answer

The valence electrons are the outermost electrons and are the ones involved in bonding and forming lone pairs. The inner-shell (core) electrons are held tightly to the nucleus and do not influence the molecular geometry, so they can be ignored when applying VSEPR theory.

Question 3

Is VSEPR theory always accurate?

Accepted Answer

VSEPR is a simple model that is remarkably effective for predicting the shapes of a vast number of molecules. However, it is a model, not a perfect law. For some very large or complex molecules, or those with heavy central atoms, other factors can come into play, and the predictions may be less accurate. For A-Level Chemistry, VSEPR theory is the primary tool and is considered accurate for the molecules you will encounter.

Shapes of molecules

What you need to know

Electron Repulsion Rules