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Homologous Families

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. IMF (van der Waals/Dispersion) increases.

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Homologous Families

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  1. Homologous Families Properties & Uses

  2. 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. • IMF (van der Waals/Dispersion) increases

  3. 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 • High vapor pressures

  4. Properties of Alkenes & Alkynes • Nonpolar – low solubility in H2O • Fairly low M.P. & B.P. • More reactive than alkanes • Multiple Bond site of reactivity. • USES: • 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.

  5. Cycloalkanes • Ring structures with general formula: CnH2n

  6. Naming Cycloalkanes • Parent Chain • 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. • Numbering the Cycloalkanes • 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.

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

  8. Hydrocarbons from Earth • Natural Gas • Composed of 80% methane, 10% ethane, 4% propane, and 2% butane • Separated by liquefraction • Readily undergo Combustion • 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.

  9. Hydrocarbons from Earth • Petroleum • 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. • 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.

  10. Fractional Distillation

  11. 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

  12. In the Laboratory… http://www.chem-ilp.net/labTechniques/FractionalDistillationlAnimation.htm

  13. Boiling Point and Carbon Chain

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

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