1. Lecture 43 Molecular Shapes Ozgur Unal 1

2.  Using the formula or the lewis structure of the following molecule, can you determine its three-dimensional shape? CH4H2O CO2H2 2  The shape of a molecule determines many of its physical and chemical properties.  After the lewis structure is drawn, we can determine the molecular shape of a molecule.  The model used to determine the molecular shape is referred to as the Valence Shell Electron Pair Repulsion Model, or VSEPR model.

3.  The electron pairs in a molecule repel one another.  These forces cause the atoms in a molecule to be positioned at a fixed angles relative to one another.  The angle formed by two terminal atoms and the central atom is a bond angle. 3  Electron pairs in a molecule are located as far apart as they can be.  Two pairs form a linear shape.  Three pairs form a trigonal planar shape.  Four pairs form a tetrahedral shape.  Check out Figure 8.18.

4.  A hybrid occurs when two things are combined and the result has characteristics of both.  Example: Hybrid automobile  During chemical bonding, different atomic orbitals undergo hybridization.  Hybridization is a process in which atomic orbitals mix and form new identical hybrid orbitals. 4 Example: CH4  Carbon atom has 4 valence electrons  2s 2 and 2p 2  These four electrons are in a hybrid sp 3 orbital.  The hybrid orbital is called sp 3 because the four hybrid orbitals form from one s orbital and three p orbitals.

5.  The total number of atomic orbitals that mix and form the hybrid orbital equals the total number of pairs of electrons.  Examples:  PH3  sp 3 hybrid orbital  H2O  sp 3 hybrid orbital  NbBr5  sp 3 d hybrid orbital  SF6  sp 3 d 2 hybrid orbital  For the bond angles, check out Table 8.6  Note that single, double and triple bonds contain only 1 hybrid orbital. 5  Example: What is the shape of a oxygen dichloride molecule? Identify the bond angle and hybrid orbitals.

6.  CO2 molecule 6