1. Chapter 10 Properties of Solids and Liquids
10.2 Shapes of Molecules and Ions (VSEPR Theory)
Learning Goal Predict the three- dimensional structure of a molecule or a polyatomic ion and classify it as polar or nonpolar.

2. VSEPR
In the valence shell electron repulsion theory (VSEPR), the three-dimensional shape of a molecule is determined by
drawing the electron-dot formula
counting the number of electron groups (one or more electron pairs) around the central atom
placing the electron groups as far apart as possible around the central atom

3. VSEPR
According to VSEPR theory, the shape of a molecule is determined by the
number of electron groups surrounding the central atom
number of atoms bonded to the central atom

4. VSEPR—Two Electron Groups
Central atoms with two electron groups (two double bonds) such as CO2 have a
linear electron-group geometry
linear shape with a bond angle of 180° to minimize repulsion

5. VSEPR—Three Electron Groups
Central atoms with three electron groups (two single bonds, one double bond) such as H2CO have a
trigonal planar electron-group geometry
trigonal planar shape with a bond angle of 120° to minimize repulsion

6. VSEPR—Three Electron Groups
Central atoms with three electron groups (a single bond, double bond, lone pair) such as SO2 have a
trigonal planar electron-group geometry
bent shape with a bond angle of 120° to minimize repulsion

7. VSEPR—Four Electron Groups
Central atoms with four electron groups (four single bonds) such as CH4 have a
tetrahedral electron-group geometry
tetrahedral shape with a bond angle of 109° to minimize repulsion
The carbon-hydrogen dash indicates the bond is behind the plane of the paper,
and the wedge indicates the carbon-hydrogen bond is in front of the paper plane.

8. VSEPR—Four Electron Groups
Central atoms with four electron groups (three single bonds, one lone pair) such as NH3 have a
tetrahedral electron-group geometry
trigonal pyramidal shape with a bond angle of 109° to minimize repulsion
The wedge-dash notation represents the three-dimensional shape of the molecule.

9. VSEPR—Four Electron Groups
Central atoms with four electron groups (two single bonds, two lone pairs) such as H2O have a
tetrahedral electron-group geometry
bent shape with a bond angle of 109° to minimize repulsion
The wedge-dash notation represents the three-dimensional shape of the molecule.

10. Molecular Shapes

11. Molecular Shapes

12. Guide to Predicting Molecular Shape (VSEPR Theory)

13. Learning Check
Use VSEPR theory to predict the shape of N2O.

14. Solution
Use VSEPR theory to predict the shape of N2O. Step 1 Draw the electron-dot formula. In the electron-dot structure with 16 e−, octets are acquired using two double bonds in the central N atom.

15. Solution
Use VSEPR theory to predict the shape of N2O. Step 2 Arrange the electron groups around the central atom to minimize repulsion. Repulsion is minimized with two electron groups at 180°, a linear arrangement.

16. Solution
Use VSEPR theory to predict the shape of N2O. Step 3 Use the atoms bonded to the central atom to determine the molecular shape. The shape of a N2O molecule with two bonded atoms and no lone pairs on the central N is linear.

17. Learning Check
State the number of electron groups, lone pairs, and bonded atoms, and use VSEPR theory to determine the shape of the following molecules:
(1) tetrahedral (2) trigonal pyramidal
(3) bent
PF3 B. H2S
CCl4 D. PO43–

18. Solution
State the number of electron groups, lone pairs, and bonded atoms, and use VSEPR theory to determine the shape of the following molecules:
(1) tetrahedral (2) trigonal pyramidal
(3) bent
A. PF3 4 electron groups, 3 bonded atoms, lone pair, trigonal pyramidal (2)
H2S 4 electron groups, 2 bonded atoms, lone pairs, bent (3)

19. Solution
State the number of electron groups, lone pairs, and bonded atoms, and use VSEPR theory to determine the shape of the following molecules:
(1) tetrahedral (2) trigonal pyramidal
(3) bent
C. CCl4 4 electron groups, 4 bonded atoms, lone pairs, tetrahedral (1)
PO43– electron groups, 4 bonded atoms, lone pairs, tetrahedral (1)