What Do You Think?

1. What Do You Think? • Provide the Lewis structure for CH4. • Give the orbital notation for a carbon atom. • Describe the inconsistency that exists between the number of bonds that carbon forms and its electron arrangement.

2. Hybridization • VSEPR theory is useful for predicting and explaining the shapes of molecules. • A step further must be taken to explain how the orbitals of an atom are rearranged when the atom forms covalent bonds. • Consider CH4 • 4 equivalent bonds that form a tetrahedral molecule • Issue with atomic orbitals and overlap • Only two half-filled orbitals yet we know that carbon wants to form 4 covalent bonds.

3. How does carbon form four equivalent, tetrahedrally arranged, covalent bonds? • To achieve four equivalent bonds, carbon’s 2s and three 2p orbitals hybridize to form four new, identical orbitals called sp3 orbitals. • Hybridization – mixing of two or more atomic orbitals of similar energies on the same atom to produce new hybrid atomic orbitals of equal energies. • In this process, the number of hybrid orbitals equals the number of atomic orbitals that are mixed.

4. This usually occurs only with the central atom in a molecule of polyatomic ion. • In order to produce hybrid orbitals, electrons are “promoted” to empty orbitals then these half-filled orbitals hybridize. • Hybrid orbitals have a different shape compared to the original atomic orbitals used to make them.

5. The Formation of sp3 Hybrid Orbitals

6. In the case of CH4 • Electron promoted from 2s to 2p • This creates 4 half-filled orbitals • These orbitals hybridize to form 4 equivalent orbitals • Since we mixed an s-orbital and three p-orbitals, we produce 4 equivalent “sp3” orbitals.

7. The four (s + p + p + p) hybrid orbitals in the sp3-hybridized methane molecule are equivalent: they all have the same energy, which is greater than that of the 2s orbital but less than that of the 2p orbitals. • Hybrid orbitals are orbitals of equal energy produced by the combination of two or more orbitals on the same atom. • Hybridization explains the bonding and geometry of many molecules.

8. The number of electron pairs on the central atom will determine the type of hybridization. • H2O • 4 electron pairs – 2 bp / 2 nbp • Each pair roughly equally spaced. • Need 4 equivalent orbitals. • Still “sp3” hybridization • Two of the hybrid orbitals hold nonbonding pairs of electrons

9. Hybridization and Multiple Covalent Bonds • Consider CH2O • Double bond formed between carbon and oxygen • Trigonal planar shape – counted as 3 electron pairs • Hybridization for 3 electron pairs is “sp2” • The second bond in the double bond involves an overlap of unhybridized p oribitals

10. The second and third bonds of a multiple bond involve unhybridized p-orbitals. • Consider: CO2 • Molecule contains two double bonds. • Linear shape – counted as 2 electron pairs • Hybridization for 2 electron pairs is “sp” • Like with molecular geometry, multiple bonds only count as one electron pair when determining hybridization.

11. The number of electron pairs contained by the central atom will determine the type of hybridization that occurs.