Using VSEPR to Predict the Shapes of Molecules
Electron
Groups on
central atom1
Electron-Group
Shape Bonds2 Lone
Pairs AXmEn3Molecular
Shape Bond
angles Polarity Hybrid
-ization Appearance
2
Linear 2 0 AX2 linear 180° nonpolar4sp
180°
3
Trigonal Planar
3 0 AX3 trigonal
planar 120° nonpolar4sp2
120°
2 1 AX2E bent <120°5 polar sp2
<120°
4
Tetrahedral
4 0 AX4 tetrahedral 109.5° nonpolar4sp3
109.5°
3 1 AX3E trigonal
pyramidal <109.5° polar sp3
<109.5°
2 2 AX2E2 bent <109.5° polar sp3
<109.5°
1 “Electron groups” include bonds, lone pairs, and odd (unpaired) electrons. A multiple bond (double bond or triple bond) counts as one electron group.
2 A multiple bond (double bond or triple bond) counts as one bond in the VSEPR model.
3 A = central atom, X = surrounding atoms, E = lone pairs
4 Molecules with this shape are nonpolar when all of the atoms connected to the central atom are the same. If the atoms connected to the central atom are different from each other, the molecular
polarity needs to be considered on a case-by-case basis.
5 Since electrons in lone pairs take up more room than electrons in covalent bonds, when lone pairs are present the bond angles are “squashed” slightly compared to the basic structure without lone
pairs.
