2. Localized electrons to Molecular orbitals

3. Hybridization The s, p, d, and f orbitals work when defining electron configurations in single atoms; however, when atoms bond the s, p, d, f arrangement no longer applies. Hydridization is the combination of s and p orbitals to make bonding orbitals.

4. Types of Hybridization HybridizationElectron density areas/Bonding areas Shapes sp 3 4Tetrahedral Trigonal pyramidal Bent 105° sp 2 3Trigonal planar Bent 120° sp2Linear

5. Bond Types Sigma (σ) bonds: Bonds formed on a line between atoms due to overlapping orbitals. Single bonds and the first bond in double and triple bonds are σ bonds. Highest energy/strongest bonds. Pi (π) bonds: Bonds formed above/below/to sides of the sigma bonds. They form between parallel orbitals. Lower energy and weaker than σ bonds.

6. Molecular Orbitals The molecular orbital model better describes much of covalent bonding in stating that new molecular orbitals (around the entire molecule) form in molecules. For instance, in H 2, there are no longer 1s orbitals for each hydrogen atom, but there is a MO 1 ( or σ 1s ) orbital filled with 2 electrons. MO 1 is lower in energy (so more stable) than the 1s orbitals, so H 2 forms. There is then a MO 2 (or σ 1s *) orbital that is higher in energy (less stable) than the 1s orbitals. This σ 1s * is an anti-bonding orbital.

7. Some simple Molecular orbital diagrams H2H2H2H2 H2-H2-H2-H2- He 2 Li 2 Be 2

8. An interruption Before we look at some more advanced molecular orbital diagrams we need to talk about magnatism Paramagnatism causes a substance to be attracted to a magnetic field. Paramagnetism is associated with unpaired electrons in molecular orbitals. Diamagnetism causes a substance to be repelled from a magnetic field. Diamagnetism is associated with paired electrons in molecular orbitals.

9. So when you get to boron… B2 expected But B2 is paramagnetic So they figured that orbitals mix and it goes like this.

10. Bond Order Bond order determines the strength of bonds. A positive bond order indicates bonds should form, and the greater the number the stronger the bond. A bond order that is zero indicates that a bond should not form. Bond order = (Number of bonding electrons-Number of anti-bonding electrons)/2 H2H2H2H2 He 2 N2N2N2N2 O2O2O2O2

11. Molecular Orbitals and Bond Order You can use these molecular orbital diagrams and bond order for heteronuclear molecules. NO NO + CN - And to even explain bond polarity. HF

12. Combining Localized electron models and Molecular orbital models When we draw resonance structures like for ozone, the only thing switching places is the double bond. So the the single σ bond can be drawn as localized and the π bond is delocalized.

13. Another example Benzene resonance structures: Benzene with delocalized π bonding: