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Hydrocarbons

Hydrocarbons. Organic Chemistry. Chemistry of carbon compounds First carbon compounds studied came from living organisms ∴ Organic Approx 90% of all compounds are organic Other compounds are referred to as inorganic. Properties of Organic Compounds.

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Hydrocarbons

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  1. Hydrocarbons

  2. Organic Chemistry • Chemistry of carbon compounds • First carbon compounds studied came from living organisms ∴Organic • Approx 90% of all compounds are organic • Other compounds are referred to as inorganic

  3. Properties of Organic Compounds • All contain carbon. Usually contain hydrogen and often oxygen and nitrogen. Sometimes sulfur, phosphorus and chlorine • All covalent compounds: • Generally insoluble in water • Have low melting and boiling points • Don’t conduct heat or electricity • Almost all burn and many are used as fuels

  4. Properties of Organic compounds • Organic reactions proceed slowly because they require the breaking and forming of strong covalent bonds. Heat and catalysts are often used to speed up organic reactions

  5. Carbon • Atomic number: 6 • Electronic configuration 2,4 • Tetravalent: Forms four covalent bonds • Bonds can be Single, Double or Triple • Can form covalent bonds with other carbon atoms to form chains of any length

  6. Hydrocarbons Hydrocarbons often contain long chains of C-C bonds

  7. Homologous series • Conform to a general formula • Have the same functional group which is the reactive part of the molecule • Each members formula differs from the one before it by CH2 • Similar chemical properties due to the functional group

  8. Example CH4 C2H6 C3H8 Propane Ethane Methane

  9. Homologous series • Physical properties gradually change as chain length changes • Melting and boiling points increase with increasing chain length • Solubility in water decreases as the chain length increases

  10. General Formula:

  11. Naming Organic compounds • Referred to as Nomenclature • Unsystematic (common) names are often used for many chemicals • Eg Acetic acid for ethanoic acid • Often a new substance will be given a common name because its structure is not completely understood

  12. Naming Organic compounds

  13. Alkanes

  14. Systematic Nomenclature • Find the longest continuous chain of carbon atoms • Identify side chains (not part of the main chain) • Number the main chain so that side chains are numbered as low as possible • If there are two or more identical groups use the following prefixes

  15. Systematic Nomenclature

  16. Side groups

  17. Structural Isomers 1 2 3 Longest C chain = 3 Propane Butane Methyl Side Chain at 2 position 2 Methyl Propane

  18. C13H28 1 2 3 4 5 6 7 8 9 Longest C Chain = 9 Nonane 2 Methyl Side Chains at 3 and 5 positions  3,5 Dimethyl Ethyl Side Chain at 6 position  6 Ethyl 6 Ethyl 3,5 Dimethyl Nonane

  19. Physical Properties of Alkanes • Non polar compounds • Insoluble in water • Less dense than water and so will float on top of the water • Dissolve in organic solvents (eg dry cleaning fluid) and in each other (eg Petrol is a mixture of alkanes) • Low melting and boiling points

  20. Chemical Properties of Alkanes • Very unreactive • Don’t react with concentrated sulfuric acid or concentrated bases • Don’t react with strong oxidants (dichromate or permanganate ions) • Will react with bromine but only if heated or in strong sunlight

  21. SubstitutionReactions • Where an atom or group of atoms is displaced by an atom or group of atoms • CH4 + Br2→ CH3Br + HBr • Non specific reaction. Can not control which hydrogen is substituted or how many are substituted • CH3Br + Br2→ CH2Br2 + HBr

  22. Substitution reactions • Very slow with heat or sunlight • Product is a mixture of bromoalkanes • Products would need to be separated by fractional distillation giving only a very small yield of each

  23. Combustionof Alkanes • Very useful group as fuels • Fuels burn completely when there is sufficient oxygen, forming CO2and H2O • If oxygen is limited then incomplete combustion occurs and carbon (soot) and carbon monoxide (CO) are formed as well as CO2 & H2O

  24. Combustion of Alkanes • Incomplete combustion is less efficient and so produces less energy per mole that complete combustion

  25. Balancing Combustion Equations • Write correct formula Alkane + O2→ CO2 + H2O • Balance carbon • Balance hydrogen • Balance oxygen (Fractional coefficients are acceptable in combustion equations)

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