1. Chapter 20 Organic Chemistry Organic chemistry = the study of compounds containing carbon and their properties. Carbon forms many biomolecules (molecules that maintain and reproduce life) Carbon and silicon form the basis of most natural substances.

2. 20.1 Carbon bonding Because carbon has four valence electrons, it can form four covalent bonds. A unique feature of carbon is its ability to form strong bonds with other carbons to form long chains or rings of various length. Carbon forms single, double, and triple bonds to achieve a filled octet.

3. 20.2 alkanes The simplest organic compounds are hydrocarbons, compounds containing only carbon and hydrogen. saturated hydrocarbons, hydrocarbons with only single bonds between the carbon atoms. (alkanes) unsaturated hydrocarbons, hydrocarbons that contain double or triple bonds between carbon atoms.

4. Alkanes The alkanes are acyclic, saturated hydrocarbons that form a homologous series of compounds, with the general formula C n H 2n+2. The simplest hydrocarbon is methane, CH 4. molecular formula structural formula

5. Figure 20.1: Methane is a tetrahedral molecule.

6. Alkanes The structural formulas for the first four straight-chain (or normal) alkanes are shown below. (Not really straight because of the tetrahedron shape. C-C bonds have a 109.5 o angle). methaneethanepropanebutane

7. Figure 20.3: Structure of propane.

8. Figure 20.3: Structure of butane.

9. Alkanes condensed structural formulas methaneethanepropanebutane

10. 20.3 Isomers In addition to straight-chain alkanes, branched-chain alkanes are possible. Note that isobutane, C 4 H 10, has the same molecular formula as normal butane. Butane and isobutane are structural isomers, compounds with the same molecular formula but different structural formulas. (Different structure means different properties.)

11. Models of isobutane and butane.