Homologous Families Properties & Uses

Properties of Alkanes  Change systematically with number of C’s  As the number of C’s increases, the boiling point increases. The molecules get heavier & harder to change into the gas phase. The molecules get heavier & harder to change into the gas phase. IMF (van der Waals/Dispersion) increases IMF (van der Waals/Dispersion) increases

Properties of Alkanes  Low Reactivity  Except readily undergo combustion – fuels  Nonpolar – Don’t dissolve well in water.  Low melting pts & boiling pts. M.P. & B.P. increase with molecular mass M.P. & B.P. increase with molecular mass  High vapor pressures

Properties of Alkenes & Alkynes  Nonpolar – low solubility in H 2 O  Fairly low M.P. & B.P.  More reactive than alkanes Multiple Bond  site of reactivity. Multiple Bond  site of reactivity.  USES: Ethene causes fruits to ripen; used as starting material in the synthesis of polyethylene. Ethene causes fruits to ripen; used as starting material in the synthesis of polyethylene. Ethyne, or acetylene, is used as a fuel in welding torches. Ethyne, or acetylene, is used as a fuel in welding torches.

Cycloalkanes  Ring structures with general formula: C n H 2n

Naming Cycloalkanes  Parent Chain Use the cycloalkane as the parent chain if it has a great number of carbons than any alkyl substituent. Use the cycloalkane as the parent chain if it has a great number of carbons than any alkyl substituent. Otherwise, use the alkyl chain as the parent and cycloalkane as substituent. Otherwise, use the alkyl chain as the parent and cycloalkane as substituent.  Numbering the Cycloalkanes Start with a substituted carbon so it has the lowest number and go in direction of lowest numbers. Start with a substituted carbon so it has the lowest number and go in direction of lowest numbers. When two or more alkyl groups are present, number according to alphabetical order. When two or more alkyl groups are present, number according to alphabetical order.

Aromatic Hydrocarbons  Contain one or more benzene rings  Have strong, pungent odors  Produced by substitution on benzene ring

Hydrocarbons from Earth  Natural Gas Composed of 80% methane, 10% ethane, 4% propane, and 2% butane Composed of 80% methane, 10% ethane, 4% propane, and 2% butane Separated by liquefractionSeparated by liquefraction Readily undergo Combustion Readily undergo Combustion Fracking utilizes water to extract oil and natural gas from shale and tight-rock formations.Fracking utilizes water to extract oil and natural gas from shale and tight-rock formations. Creates micro-fractures that are held together by the grains of sand. Creates micro-fractures that are held together by the grains of sand.

Hydrocarbons from Earth  Petroleum Refining process starts with the distillation of petroleum (crude oil) to divide it into fractions according to their boiling point. Refining process starts with the distillation of petroleum (crude oil) to divide it into fractions according to their boiling point. Cracking is a controlled process by which hydrocarbons are broken down into smaller, more useful molecules.Cracking is a controlled process by which hydrocarbons are broken down into smaller, more useful molecules. Needs high heat and a catalyst in the absence of oxygen. Needs high heat and a catalyst in the absence of oxygen. Used for high yield of gasoline and starting material for a variety of chemical synthesis reactions. Used for high yield of gasoline and starting material for a variety of chemical synthesis reactions.

Fractional Distillation

 Separates a mixture into a number of different parts  fractional  Works because different substances in the mixture have different boiling points  Gases condense at the top, liquids in the middle, solids settle to the bottom  Hydrocarbons with small molecules make better fuels: volatile, flow easily and are easily ignited

In the Laboratory…

Boiling Point and Carbon Chain

Hydrocarbons from Earth  Coal Formed from decayed plants over millions of years. First stage is the formation of peat. Formed from decayed plants over millions of years. First stage is the formation of peat. Consists largely of aromatic compounds of large molar mass. Consists largely of aromatic compounds of large molar mass.