Shapes with double bonds and more than one centre

5 minAS Level3.5.13.5.2

AI-drafted, independently checked · not yet teacher-reviewed

By the end of this lesson

By the end you can predict the shape and bond angles around each central atom in molecules with double or triple bonds, such as $\text{C}_2\text{H}_4$ , $\text{HCN}$ , $\text{SO}_2$ and $\text{CH}_3\text{OH}$ .

Big molecules have a shape at every atom

Ethanol doesn't have "a" shape the way water does. It has a shape around each C and around the O.

So work one atom at a time: treat each atom with two or more neighbours as a centre, and run VSEPR on it.

Rule for multiple bonds

A double or triple bond counts as one region of electron density. All its electrons sit between the same two atoms, pointing the same way.

So you count regions, not electrons:

regions around the atom	lone pairs	shape there	VSEPR-predicted angle
2	0	linear	180°
3	0	trigonal planar	120°
4	0	tetrahedral	109.5°
4	2	non-linear	104.5°

The angles in these tables are idealized VSEPR predictions, not exact measured values for every molecule.

Quick check

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