National 5 Chemistry

1. National 5 Chemistry Unit 2 – Nature’s Chemistry Section 6 – Homologous Series

2. Section 6 – Homologous SeriesPupils should be able to… • State that hydrocarbons are compounds of hydrogen and carbon • Define a homologous series • State that alkanes are a homologous series of saturated hydrocarbons • Define saturated hydrocarbons as having single carbon-carbon bonds • Represent the alkanes by a general formula • Describe the pattern of physical properties of a homologous series such as melting and boiling points. • State common uses of alkanes, chemical and physical properties • Explain this pattern of physical properties in relation to the increasing strength of intermolecular forces as molecular size increases

3. What are Hydrocarbons? • A hydrocarbon is a molecule which contains only the elements Carbon and Hydrogen. • Hydrocarbons are obtained from the Fractional Distillation of crude oil. • We use them for fuels in cars (octane) and in cookers (methane).

4. How do we Group all these Hydrocarbons Together?

5. What is a Homologous Series? Homologous Series • A group of chemically similar compounds which can be represented by a general formula. • Physical properties change gradually as you go down the series • There are three groups that we are going to look at Alkanes 2. Alkenes 3. Cycloalkanes

6. Alkanes Methane Monsters Ethane Eat Propane Pupils Butane But Pentane Prefer Hexane Hairy Heptane Haggis Octane Occasionally

7. Alkane Structure 3D Full Structural  2D Full Structural Formula Formula

8. Alkanes • Each member can be represented in three different ways: Methane Propane • Full Structural Formula • Shortened Structural Formula • Molecular Formula

9. Alkane Information • The Alkanes are a family of hydrocarbons and all share the same chemical properties: • Single Carbon to carbon bonds (- C – C -) • They are insoluble in water • Burn in oxygen to produce carbon dioxide and water • All end in -‘ane’ • Saturated hydrocarbons • All share a General Formula

10. Trends of the Alkanes • CH4 • CH4 • C3H8 • - 42 CH3CH2CH3

11. Trends of the Alkanes

12. Trends of the Alkanes

13. Alkane Trend Summary

14. Alkanes General Formula The no. of Hydrogen atoms = 2 times the number of Carbon atoms plus 2 General Formula for alkanes is CnH2n+2

15. Alkanes – Physical Properties • M.p/B.p– gradual increase from methane to octane • Viscosity - increases as you move down the group • Colour – darker in colour as you move down the group • Density – less dense than water

16. Intermolecular Forces between Molecules • Larger molecules have more places for intermolecular forces. • More intermolecular forces requires more energy to overcome these forces thus the larger the molecule the higher the melting and boiling point.

17. Uses of Alkanes https://www.bbc.co.uk/bitesize/guides/zw4tw6f/revision/1

18. Section 6 – Homologous SeriesPupils should be able to… • State that alkenes are a homologous series of unsaturated hydrocarbons • State that alkenes contain the C = C double bond • State common uses of alkenes, chemical and physical properties • Represent the alkenes by a general formula • Write molecular as full and shortened formula

19. Alkenes XMonsters EtheneEat Propene Pupils ButeneBut Pentene Prefer HexeneHairy HepteneHaggis OcteneOccasionally

20. Alkene Structure • 3D Full Structural  2D Full Structural Formula Formula

21. Alkenes • Each member can be represented in three different ways: Ethene Propene • Full Structural Formula • Shortened Structural Formula • Molecular Formula

22. Alkenes • The Alkenes are a family of hydrocarbons and all share the same chemical properties: • Double Carbon to carbon bonds ( - C = C - ) • All end in -‘ene’ • Unsaturated hydrocarbons • All share a General Formula

23. Trends of Alkenes

24. Trends of Alkenes

25. Trends of Alkenes

26. Alkene Trend Summary

27. Alkene General Formula The no. of Hydrogen atoms = 2 xthe number of Carbon atoms General Formula for alkenes is CnH2n

28. Properties of Alkenes • Physical Properties • The alkenes increase in size down the group • Their melting and boiling points increase down the group • Chemical Properties • All burn completely to produce carbon dioxide and water • Undergo addition reactions

29. Uses of Alkenes • Making polymers (plastics) • Industrial production of ethanol • Fuels • Solvents https://www.bbc.co.uk/bitesize/guides/zw4tw6f/revision/3

30. Section 6 – Homologous SeriesPupils should be able to… • State that cycloalkanes are a homologous series of saturated cyclic hydrocarbons • State common uses of cycloalkanes, chemical and physical properties • Represent the cycloalkanes by a general formula

31. Cycloalkanes Information • Cycloalkanes are a homologous series of cyclic hydrocarbon Uses Cyclohexane for making nylon Solvents for compounds that don’t dissolve in water Used in motor oil, kerosine, diesel and other heavy oils

32. Cycloalkanes X Monsters X Eat CyclopropanePupils CyclobutaneBut CyclopentanePrefer Cyclohexane Hairy CycloheptaneHaggis CyclooctaneOccasionally

33. Cycloalkane Structure • 3D Full Structural  2D Full Structural Formula Formula

34. Cycloalkanes • Each member can be represented in three different ways: Cyclopropane • Full Structural Formula • Shortened Structural Formula • Molecular Formula

35. Cycloalkanes Information • The Cycloalkanes are a family of hydrocarbons and all share the same chemical properties: • Single Carbon to carbon bonds ( - C – C - ) • All end in -‘ane’ • Saturated hydrocarbons • All share a General Formula • Instead of forming straight chain molecules they form circular or cyclical molecules. • Burn to produce carbon dioxide and water • Cycloalkanes are isomers of alkenes

36. Physical Properties • They increase in size • The m.p/b.p increases as the size increases

37. Trends in Cycloalkanes • C4H8 • CH2CH2CH2CH2 • CH2CH2CH2CH2CH2

38. Trends in Cycloalkanes • CH2CH2CH2CH2CH2CH2 • C7H14 • CH2CH2CH2CH2CH2CH2CH2 • CH2CH2CH2CH2CH2CH2CH2CH2

39. Cycloalkane Trend Summary

40. Cycloalkanes – General Formula The number of Hydrogen atoms = 2 times the number of Carbon atoms General Formula for cycloalkanes is CnH2n https://www.bbc.co.uk/bitesize/guides/zw4tw6f/revision/4

41. Section 6 – Homologous SeriesPupils should be able to… • Describe how to distinguish an unsaturated and saturated compound using bromine solution • State that alkenes can undergo addition reactons: • With hydrogen forming alkanes, known as hydrogenation • With halogens forming dihaloalkanes • With water forming alcohols known as hydration

42. How can we tell these Hydrocarbons apart? • We need to be able to experimentally tell whether a hydrocarbon is an alkane, an alkene or even a cycloalkane so how might we do this? • What chemical property do they have that is different that we may be able to exploit? Answer: the reactive C=C bond which we can break. We use the Bromine Test.

43. Testing for Saturation Collect: goggles, three test tubes, bromine solution, test tube rack, an alkane, alkene and cycloalkane for testing. • Method: add 2cm3 alkane to a test tube then add in a few drops of bromine water, shake and observe what happens • Repeat with the alkene and the cycloalkane then record your results in a table.

44. Conclusion: Alkanes decolourise red/brown bromine solution _______ _______ therefore alkanes are saturated hydrocarbons. Alkenes decolourise red/brown bromine solution ________ therefore alkenes are unsaturated hydrocarbons very slowly quickly

45. Testing for Unsaturation Alkane + Bromine Cycloalkane + Bromine Alkene + Bromine

46. Why?

47. Addition ReactionDihaloalkane Pentene Bromine 1,2 -dibromopentane Colourless Red/Orange Colourless This is called an Addition Reaction

48. Addition Reaction Hydrogenation Pentene Hydrogen Pentane

49. Addition Reaction Hydration Pentene Water Pentanol

50. Saturation Summary • We can use Bromine solution to test for unsaturation in an addition reaction • Alkanes are saturated hydrocarbons. Alkanes decolourise red/brown bromine solution very slowly • Alkenes are unsaturated hydrocarbons. Alkenes decolourise red/brown bromine solution quickly