1. Bonding Theories
Part 2: VSEPR Theory

2. Objectives
Describe how VSEPR theory helps predict the shapes of molecules
Identify ways in which orbital hybridization is useful in describing molecules

3. Important Vocabulary
Tetrahedral angle
VSEPR theory
Hybridization

4. VSEPR Theory
States that the _______ between electron pairs causes molecular shapes to adjust so that the ___________ pairs stay as far apart as possible
For example, methane molecules are three-dimensional
The hydrogen in the molecule are at the four corners of a geometric solid called a regular tetrahedron
In this arrangement, all of the H-C-H angles are 109.5°, the _________________

5. Methane
The four shared pairs are NOT at the maximum distance apart when on a flat plane
Instead, they position themselves at the corners of a tetrahedron
Its shape, then is tetrahedral

6. Electron Pairs & Molecular Shape
_______________ of electrons are also important in predicting the shapes of molecules
For example: CO2
The two shared pairs that form each double bond repel each other and remain as far apart as possible
Thus, this molecule is __________

7. Carbon Dioxide

8. What about BF3? Remember _____________________________
The three unshared pairs of electrons on each F atoms will repel each other to the maximum distance apart.
Its molecular shape is called _______________

9. BF3

10. What about Unshared Electron Pairs?
When the _________ has an _______ pair of electrons, they influence the shape of the molecule
In VSEPR theory, unshared pairs occupy more space around the central atom than shared pairs
Thus, the shared pairs and the unshared pair cause the shape to be ________

11. Examples of Bent Molecules

12. 9 Possible Molecular Shapes

13. Predicting Molecular Shapes
Draw the Lewis structure for the molecule
Count the shared and unshared pairs of electrons around the central atom
Use VSEPR theory to find the shape that allows the shared and unshared pairs of electrons to be spaced as far apart as possible
Verify the structure by making sure that all the atoms, except hydrogen, obey the octet rule

14. Examples
1. BeCl2 2. SO SO3 4. PF5

15. Hybrid Orbitals
The VSEPR theory works well when accounting for molecular shapes, but it does not help much in describing the types of bonds formed
_______________________ provides information about both molecular bonding and molecular shape
In hybridization, several ______________ mix to form the same total number of equivalent hybrid orbitals

16. Hybridization Involving Single Bonds
Considering methane CH4
The carbon atom’s outer electron configuration is 2s22p2
But one of the 2s electrons is promoted to a 2p orbital
This gives one 2s electron and three 2p electrons, allowing carbon to bond to 4 hydrogen atoms
All of these bonds are identical and can be explained by orbital hybridization

17. Hybridization Involving Single Bonds
The one 2s orbital and three 2p orbitals of a carbon atom mix to form four _____________
These are at the tetrahedral angle of 109.5°
The sp3 orbitals extend further into space than either s or p orbitals, allowing a great deal of overlap with the hydrogen 1s orbitals
The 8 available valence electrons fill the molecular orbitals to form four C‒H sigma bonds
The overlap results in unusually strong covalent bonds

18. Hybridization of Methane

19. Hybridization Involving Double Bonds
Ethene is a relatively simple molecule that has one carbon-carbon double bond and 4 carbon- hydrogen single bonds
The bond angles in ethene are 120°
Two ______________ form from the combination of one 2s and two 2p atomic orbitals
Five sigma bonds and one pi bond hold the molecule together

20. Hybridization of Ethene

21. Hybridization Involving Triple Bonds
Ethyne (C2H2) also called acetylene, forms a carbon-carbon triple bond
It is a linear molecular
It creates two __________ for each carbon
In total 3 sigma bonds and two pi bonds hold the molecule together

22. Hybridization of Ethyne