2.7Compound Structure and Properties

VSEPR and Hybridization — AP CHEMISTRY Revision Notes & Topical Questions

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Lesson summary

2.7 VSEPR and Hybridization — Notes — AP CHEMISTRY notes: Use VSEPR theory and hybridisation to predict molecular geometry, polarity and the types of bonds in covalent species.VSEPR uses Coulombic repulsion between electron domains to predict the arrangement of electron pairs aro…

Four domains
Five domains
Six domains
Sigma bond
An electron domain is a bond or a lone pair, and a multiple bond counts as one domain
Lone pairs repel more than bonding pairs, so they reduce bond angles

Section 1 of 10VSEPR theory

VSEPR uses Coulombic repulsion between electron domains to predict the arrangement of electron pairs around a central atom.

An electron domain is a bond or a lone pair, and a multiple bond counts as one domain.

Lone pairs repel more than bonding pairs, so they reduce bond angles.

Both Lewis diagrams and VSEPR are used to predict structure of covalent molecules and polyatomic ions.

Section 2 of 10Electron-domain geometry

Domains	Electron-domain geometry	Angle	Hybridisation
2	Linear	180°	sp
3	Trigonal planar	120°	sp²
4	Tetrahedral	109.5°	sp³
5	Trigonal bipyramidal	90° and 120°	Not assessed in detail
6	Octahedral	90°	Not assessed in detail

Section 3 of 10Molecular geometry

Molecular geometry describes only the positions of the atoms.

Four domains

Four domains no lone pair is tetrahedral (CH₄, 109.5°), one lone pair is trigonal pyramidal (NH₃, about 107°), two lone pairs is bent (H₂O, about 104.5°).

Five domains

Five domains seesaw (one lone pair), T-shaped (two) and linear (three).

Six domains

Six domains square pyramidal (one lone pair) and square planar (two).

Section 4 of 10Sigma and pi bonds

A single bond is one sigma (σ) bond; a double bond is one σ and one pi (π); a triple bond is one σ and two π.

Sigma bonds form by end-to-end overlap; pi bonds form by side-by-side overlap of unhybridised p orbitals.

The overlap is stronger in sigma bonds, so sigma bonds have greater bond energy than pi bonds.

Pi bonds prevent rotation about double bonds.

Section 5 of 10Polarity

Polarity

A molecule is polar if it has polar bonds whose dipoles do not cancel because of an asymmetrical shape.

H₂O is polar, whereas CO₂ is nonpolar.

Symmetrical shapes with identical terminal atoms are nonpolar, namely linear, trigonal planar, tetrahedral, square planar and octahedral.

Section 6 of 10Predicting shape

Draw the Lewis diagram.

Count the electron domains on the central atom.

Assign electron-domain geometry and hybridisation.

Name the molecular geometry from the bonding domains only.

Adjust the bond angles for lone pairs and decide polarity from symmetry.

Section 7 of 10Examples

Species	Domains	Hybridisation	Shape	Angle	Sigma and pi bonds
CO₂	2	sp	Linear	180°	2σ, 2π
BF₃, C₂H₄	3	sp²	Trigonal planar	120°	Ethene: 5σ, 1π
CH₄	4	sp³	Tetrahedral	109.5°	4σ
NH₃	4	sp³	Trigonal pyramidal	about 107°	3σ
H₂O	4	sp³	Bent	about 104.5°	2σ

Section 8 of 10More from the specification

Section 9 of 10Key terms

Term	Meaning
VSEPR	Electron domains arrange as far apart as possible to minimise repulsion.
Electron domain	A bond (single, double or triple) or a lone pair around a central atom.
Hybridisation	Mixing of atomic orbitals into equivalent hybrid orbitals.
Sigma bond	Bond from head-on orbital overlap, present in every single bond.
Pi bond	Bond from side-on overlap of p orbitals, present in double and triple bonds.
Molecular geometry	Arrangement of the atoms only.

Section 10 of 10Exam technique

Counting a double bond as two electron domains — a multiple bond is one domain

Giving the electron-domain geometry when asked for the molecular shape

Assuming polar bonds always give a polar molecule — symmetry can cancel dipoles

Describing a pi bond as head-on overlap — it is side-by-side overlap

Last updated: 18 October 2026