Organic Chemistry Chapter 10: The Alkanes Part 02: The Alkanes

Organic Compounds Hydrocarbons Aliphatic Alkanes Aromatic CycloalkanesAlkenesAlkynes UnsaturatedSaturated

Hydrocarbons Simplest family of organic compounds Carbon and hydrogen only Aliphatic or aromatic – Aliphatic Saturated or unsaturated – Aromatic Rings, double bonds, distinctive odors

Saturated vs. Unsaturated Saturated hydrocarbons – Single bonds only – Alkanes or cycloalkanes Unsaturated hydrocarbons – At least one double or triple bond – Alkenes (double bond) or alkynes (triple bond)

Alkanes Simplest family General formula: C n H 2n+2 Homologous series – Differ by constant number of atoms ( CH2 ) Names: Greek prefix for # of Carbon atoms + -ane ending

CH 4 (g) C 2 H 6 (g) C 3 H 8 (g) C 4 H 10 (g) C 5 H 12 (l) The First 10 Alkanes methane ethane propane butane pentane

C 6 H 14 (l) C 7 H 16 (l) C 8 H 18 (l) C 9 H 20 (l) C 10 H 22 (l) The First 10 Alkanes, cont. hexane heptane octane nonane decane These are all molecular formulas. Doesn’t give information about structure or geometry, which is very important.

Molecular formula Carbon Skeleton Complete structural formula Condensed structural formula Butane

Each Carbon bonded to 4 atoms Tetrahedral geometry Single bonds = free rotation Zig-zag conformation Best represented by ball and stick models Molecular Geometry

Petroleum – High molar mass alkanes (more carbon atoms) Natural gas – Low molar mass alkanes (few carbon atoms) methane, ethane, propane, butane Separated by fractional distillation – Based on differences in boiling points (which is based on molar masses) Sources of Alkanes

Nonpolar Insoluble in water Most are less dense than water – Density increases with molar mass No or low odor Colorless Tasteless Physical Properties of Alkanes

Low reactivity Flammable Chemical Properties of Alkanes

Not very toxic, but... Can dissolve lipid layer in lungs causing pneumonia Effect on skin – Lower molar mass alkanes dry out skin – Higher molar mass alkanes sold as mineral oils, petroleum jelly Physiological Properties of Alkanes

Boiling points and melting points dependent on intermolecular forces of attraction – All alkanes are nonpolar – Only type of IMFA is London forces – London forces increase as the number of atoms in the molecule increase Methane has minimal London forces. Methane is a gas at room temperature. IMFA for alkanes