hberla8atgh6snneeugasY8Poo A HHHH 1 The Big Picture 1.o of then 2.The overlap model for bonding: the valence electron count with the 1 Important Concepts Important Concepts 1. Chemistry of carb 7. Shape of Molecules-Strongly by 8. 3. nicBoadsg-dReetfomcoucmbicatactono Covalent Bonds -Result from electron sharing Re8onanCan5omeYeeaacee nd Length rage distance between two oar Bonds 9 9 Several types of drawings are used to represent molecular structures. Tetrahedral carbon structures can be accurately represented in three dimensions using the dashed-wedged line notation. 1 The Big Picture 1. The importance of Coulombs Law: • Atomic attraction • Relative electronegativity • Electron repulsion model for shapes of molecules • Choice of dominant resonance contributors. 2. The tendency of electrons to spread out (delocalize): • Resonance forms • Bonding overlap 3. The correlation of the valence electron count with the Aufbau principle. • Associated stability of the elements in noble gas-octet￾closed-shell configurations obtained by bond formation. 1. The characteristic shapes of atomic and molecular orbitals: 1. Provides a feeling for the location of the “reacting” electrons around the nuclei. 2. The overlap model for bonding: • Allows a judgment of energetics, directions and overall feasibility of reactions. 1 Important Concepts 1. Organic Chemistry – Chemistry of carbon and its compounds. 2. Coulomb’s Law – Relates attractive or repulsive force between charges to the distance between them. 3. Ionic Bonds – Result from coulombic attraction of oppositely charged ions. 4. Covalent Bonds – Result from electron sharing between two atoms. 5. Bond Length – Average distance between two covalently bonded atoms 6. Polar Bonds – Formed between atoms of differing electronegativity 1 Important Concepts 7. Shape of Molecules – Strongly Influenced by electron repulsion. 8. Lewis Structures – Describe bonding using valence electron dots. Hydrogen receives a duet while other atoms receive an octet. Charge separation should be minimized but may be enforced by the Octet Rule. 9. Resonance Forms – When a structure is described by two or more Lewis structures differing only in their electron positions. The actual molecule is an average of the resonance forms. Some resonance structures may be more important that others. 10. De Broglie Relation – Relates wavelength of an electron to its mass and velocity