2.2.2 The Shapes of Simple Molecules and Ions

Electron-pair repulsion theory: electron pairs….

repel each other as far away as possible

Electron-pair repulsion theory: the shape of the molecule/ion is determined by….

the number of electron pairs on the central atom

Electron-pair repulsion theory: lone pairs…

repel more than bonded pairs as they sit closer to the nucleus

Electron-pair repulsion theory: the total number of electron pairs and how many of them are lone/bonding pairs determines….

the shape and the bond angles

How do you work out the shape?

draw a dot and cross diagram

count number of pairs of electrons on outer shell of the central atom

This will give you the basic shape

count how many of the pairs are bonding pairs and how many are lone pairs

this will give you the final shape and the bond angles

Linear

2 boding regions, no lone pairs, bond angle 180°

Trigonal Planar

3 bonding regions, no lone pair, bond angle 120°

Tetrahedral

4 bonding regions, no lone pairs, bond angle 109.5°

Octahedral

6 bonding regions, no lone pairs, bond angle 90°

Lone Pairs repel….

more than bonding pairs this causes a reduction in the bond angle between any bonding pairs of 2.5° for each lone pair present

Trigonal Pyramidal

3 bonding regions, 1 lone pair, bond angle 107°

Non-linear/Bent

2 bonding regions, 2 lone pairs, bond angle 104.5°