1. Chapter 1 Structure and Bonding Lecture 3 I.Molecular Orbitals and Covalent Bonding A.H 2 Molecule 1)Bonds are made by the in-phase overlap of atomic orbitals 2)H 2 and He 2 Bonding a)2 A.O.’s lead to 2 M.O.’s b)Bonding Molecular Orbital is energy stabilized (-  E) c)Antibonding M.O. is energy destabilized (+  E) d)Electrons fill lowest energy M.O.’s first

2. B.Sigma and Pi Molecular Orbitals 1)Sigma Bond (  ): atomic orbitals parallel with nuclear axis 2)Pi Bond (  ): atomic orbitals perpendicular with nuclear axis II. Hybrid Orbitals A.sp Hybridization: BeH 2 1)Need unpaired electrons to form bonds 2)Promotion of electron from 2s to 2p orbital

3. 3)BeH 2 is linear not bent 4)Orbital Hybridization: mixing of A.O.’s to form an equal number of new hybrid orbitals with new geometries and energies a)Linear b)Symmetric c)Be has 2 empty p orbitals left B.sp 2 Hybrids: BH 3 1) Trigonal 2) Symmetric 3) 1 p-orbital left

4. C.sp 3 Hybrids: CH 4 1)Tetrahedral 2)No p-orbitals left D.Ethane: sp 3 hybridization in a C-C sigma bond E.Ammonia and Water: sp 3 hybridization and lone pairs F.Ethene and Ethyne:  -bonding with p-orbitals

5. III.Structures of Organic Molecules A.Structural or Constitutional Isomers = molecules with the same molecular formula, but different connectivities 1)Completely different compounds: ethanol and dimethyl ether 2)Completely different chemical and physical properties B.Drawing molecular structures Lewis/Kekule Condensed Bond-Line Dashed-Wedged Line EthanolDimethyl Ether