1. + Wave Mechanics and Covalent Bond Formation Ch 9

2. + 2 successful theories approach the formation of a covalent bond Valence Bond Theory Covalent bond is the overlapping of 2 atomic orbitals when electron spins are paired AP exam tends to focus on the VB approach Molecular Orbital Theory Considers that a molecule is similar to an atom in that both have distinct energy levels that can be populated with electrons

3. + Valence Bond Theory 2 H atoms approach & interact w/ an overlap of their atomic orbitals with e - that have opposing spins When the bond forms, the paired e - spread out over the molecule to form the final e - cloud over the nuclei. Overlap of 2 “s” orbitals – called a SIGMA ( σ )BOND - Every covalent bond has 1 & only 1 σ bond!

4. + Overlap of an “s” & a “p” orbital Overlap of 2 “p” orbitals

5. + Pi (π) bonds Occur if there are double or triple bonds in the molecule Formed by the sideways overlap of 2 “p” orbitals e - density is arranged in the 2 e - clouds, one above and one below the internuclear axis, so the e - in the π bond do NOT interfere with the σ bond Single bond – 1 σ bond Double bond – 1 σ bond & 1 π bond Triple bond - 1 σ bond & 2 π bonds

6. Which represents a double bond and which represents a triple bond?

7. + Hybrid Orbital Model VSEPR theory explains why certain molecules have the geometric shapes that are measureable in the lab. Hybrid orbitals describe how the e - might rearrange in a molecule to explain the experimental data on bond angles. Hybrid orbital – a set of orbitals with identical properties formed from the combination of 2 or more different orbitals with different energies

8. + sp 3 hybrid orbitals Ex. CH 4 Structure is tetrahedral, the C has 4 σ bonds e - configuration 1s 2 2s 2 2p 2 sp 3 hybrid orbital The “s” and 3 “p” orbitals in C reorganize into 4 sp 3 hybrid orbitals. Notice that an sp 3 orbital has energy somewhere between the 2s and the 2p

9. + sp 2 hybrid orbitals Ex. CH 2 O sp 2 hybrid orbitals The C has 3 σ bond & 1π bond Structure is trigonal planar.

10. + sp hybrid orbitals The C has 2 σ bonds & 2 π bonds It’s linear sp hybrid orbital

11. + Correspondence between hybridization and structure StructureHybrid# bonding pairs # lone pairs Linearsp20 Trigonal planarsp 2 30 Bentsp 2 21 Tetrahedralsp 3 43 Trigonal pyramidal sp 3 31 Bentsp 3 22 Scientists have NOT been able to demonstrate the existence of and importance of sp 3 d and sp 3 d 2 hybrid orbitals and are omitted from the AP Test. Therefore, all other structures will not be shown with their hybridization.