Shapes of
Molecules and
Ions
This section covers electron pair repulsion theory and the shapes of simple molecules and ions. It focuses on bonding pairs and lone pairs as charge clouds, how electron pairs arrange themselves to minimise repulsion, and how lone pairs affect bond angles.
Revision Notes
Work through each molecular shape and ion shape in a structured sequence.
Linear
Two electron pairs arranged in a straight line around the central atom.
Start revisingTrigonal Planar
Three bonding regions arranged in one plane with equal repulsion.
Start revisingTetrahedral
Four bonding pairs arranged as far apart as possible in three dimensions.
Start revisingTrigonal Pyramidal
Three bonding pairs and one lone pair give a pyramidal molecular shape.
Start revisingBent
Two bonding pairs and two lone pairs give a non-linear shape.
Start revisingTrigonal Bipyramidal
Five electron pairs arranged with axial and equatorial positions.
Start revisingOctahedral
Six bonding pairs arranged symmetrically around the central atom.
Start revisingSquare Planar
Four bonding pairs arranged in one plane with two lone pairs opposite each other.
Start revisingSquare Pyramidal
Five bonding pairs and one lone pair give a square-based pyramid.
Start revisingDistorted T
Three bonding pairs and two lone pairs give a T-shaped arrangement.
Start revisingSeeSaw
Four bonding pairs and one lone pair give a seesaw shape.
Start revising3.1.3.5 Shapes of Simple Molecules and Ions – AQA A Level Chemistry
The following AQA specification point outlines the knowledge and skills students are expected to demonstrate for molecular and ionic shapes.
Bonding pairs and lone (non-bonding) pairs of electrons as charge clouds that repel each other.
Pairs of electrons in the outer shell of atoms arrange themselves as far apart as possible to minimise repulsion.
Lone pair-lone pair repulsion is greater than lone pair-bond pair repulsion, which is greater than bond pair-bond pair repulsion.
The effect of electron pair repulsion on bond angles.
Students should be able to:
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