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Hydrocarbons

Hydrocarbons are molecules containing only hydrogen and carbon obtained from crude oil by fractional distillation. Learn about different hydrocarbon families and their unique properties such as flammability and boiling point. Dive deeper into the world of alkanes, cycloalkanes, alkenes, and more. Discover the concepts of saturation, addition reactions, isomers, and the process of cracking. Explore the fascinating world of these essential organic compounds.

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Hydrocarbons

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  1. Hydrocarbons

  2. Hydrocarbons Molecules which contain the elements HYDROGEN and CARBON ONLY Obtained from crude oil by FRACTIONAL DISTILLATION: Increasing molecular size Decreasing Flammability Increasing boiling point Increasing viscosity

  3. Hydrocarbon Families Hydrocarbons are divided up into families A family of hydrocarbons which all fit the SAME GENERAL FORMULA and which all have SIMILAR CHEMICAL PROPERTIES is called a HOMOLOGOUS SERIES Alkanes Cycloalkanes Alkenes

  4. Alkanes All members are in STRAIGHT CHAINS and have only SINGLE carbon-to-carbon bonds All members of the family have an individual name 1st part of name tells you how many carbon atoms are in the hydrocarbon: Meth = 1 But = 4 Hept = 7 Eth = 2 Pent = 5 Oct = 8 Prop = 3 Hex = 6 2nd part of name tells you which family the hydrocarbon belongs to: -ANE = Alkanes

  5. Mnemonic

  6. H C H H H Methane • Each carbon atom forms 4 bonds • Each hydrogen atom forms 1 bond

  7. Formulae CH4 CH4 C2H6 CH3 CH3 C3H8 CH3 CH2 CH3 Shortened structural Molecular Full structural

  8. General Formula CnH2n+ 2 E.g. If there are 5 carbon atoms, the number of hydrogen atoms is 2 x 5 + 2 = 12 Each family member differs by a CH2 unit:

  9. Properties This REGULAR INCREASE in a CH2 unit means that as you move through the family, there is a gradual change in PHYSICAL PROPERTIES e.g. boiling point The CHEMICAL PROPERTIES in each member of the family are all very SIMILAR e.g. flammability

  10. Titan: Saturn’s largest moon

  11. CH2 CH2 CH2 CH2 CH2 CH2 CH2 Cycloalkanes Are another HOMOLOGOUS SERIES of hydrocarbons This time, each member forms a RING shape C3H6 Cyclopropane C4H8 Cyclobutane CnH2n

  12. H H C C H H Alkenes Are another HOMOLOGOUS SERIES of hydrocarbons Each member is in a straight chain Each member contains a carbon-to-carbon DOUBLE BOND Ethene - The first member of this family CnH2n

  13. H H C C H H H H H H H H C C C H H C C C C H H H H H H Members of the Alkene Family Ethene C2H4 CH2=CH2 Propene C3H6 CH3CH=CH2 C4H8 Butene

  14. H H C C C H H H H Saturated vs Unsaturated Saturated: Alkanes, cycloalkanes Only carbon-to-carbon SINGLE bonds No other atoms will join on to the molecule Unsaturated: Alkenes Contains at least one carbon-to-carbon DOUBLE bond Other atoms can join on to the molecule

  15. 1 2 Addition Reactions Hydrocarbons with a C=C can react with other atoms to let them ADD ON. This is called an ADDITION REACTION The new atoms join on to EITHER SIDE of the DOUBLE BOND

  16. Test with bromine solution Hydrocarbon Saturated / unsaturated Br2 (aq) Test for Unsaturation Bromine solution can be used to distinguish between alkanes and alkenes, or cycloalkanes and alkenes Alkane Saturated Stays brown / red Cycloalkane Saturated Stays brown / red Alkene Unsaturated Changes from brown / red to colourless

  17. Less produced High demand Lots produced Low demand Supply vs Demand

  18. Cracking • Is used to make smaller, more useful molecules from larger molecules Bond breaks (random) High temperature

  19. Aluminiumoxide Cracked gas Alkane Cracking in the Lab • Can be done in the laboratory:

  20. H H C C C H H H H Isomers Hydrocarbons with the SAME NUMBER of atoms but DIFFERENT structures are called ISOMERS Isomers can be of hydrocarbons in the SAME FAMILY: C4H10 Or in DIFFERENT FAMILIES: C3H6

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