1. Alkenes IB Chemistry Topic 10.3

2. What is the difference between alkanes and alkenes? Which do you think would be more reactive?

3. 4.2.4 State and explain the relationship between the number of bonds, bond length and bond strength. The more pairs of Electrons that are shared between two atoms (bonds) in a molecule will make the attraction between the atoms stronger and shorter Length nm Strength (kj mol-1) C-O0.143356 C-C0.154348 C=O0.121736 C=C0.134657 C 0.120908

4. Then why are alkenes MORE reactive than alkanes???

5. 10.3 Alkenes Asmt. Stmts 10.3.1 Describe, using equations, the reactions of alkenes with hydrogen and halogens. 10.3.2 Describe, using equations, the reactions of symmetrical alkenes with hydrogen halides and water. 10.3.3 Distinguish between alkanes and alkenes using bromine water. 10.3.4 Outline the polymerization of alkenes. 10.3.5 Outline the economic importance of the reactions of alkenes.

6. 10.3.1 Describe, using equations, the reactions of alkenes with hydrogen and halogens.

7. 10.3.1 Reactions of Alkenes: The general mechanism Alkenes react with many substances to form a new substance. Catalysts, acids or other substances may be required to complete the reaction: C 2 H 4 + XY → CH 2 X CH 2 Y Process occurs by breaking the double bond.

8. Addition Reactions An addition reaction occurs when atoms are added to a molecule There are different types of addition reactions: Hydrogenation Bromination / chlorination Hydration Polymerization http://www.youtube.com/watch?v=8G1NXYZK GL0

9. 10.3.1 Reactions of Alkenes: with hydrogen Alkenes react hydrogen gas to create an alkane, using nickel as a catalyst at 150ºC: C 2 H 4 + H 2 → CH 3 CH 3

10. 10.3.1 Reactions of Alkenes: with halogens Alkenes react readily with chlorine or bromine to create a di-halo-alkane (what is this?): C 2 H 4 + 2 Cl 2 → CH 2 Cl CH 2 Cl

11. 10.3.2 Describe, using equations, the reactions of symmetrical alkenes with hydrogen halides and water.

12. 10.3.2 Reactions of Alkenes: with hydrogen halogens Alkenes react readily with hydrogen halides to create a halo-alkane: C 2 H 4 + HBr → CH 3 CH 2 Br

13. 10.3.2 Reactions of Alkenes: with water Alkenes do not react readily with water. If sulfuric acid is used (an intermediate substance will be made), an alcohol will be created : C 2 H 4 + H 2 O → CH 3 CH 2 OH Remember that H 2 O is the same as HOH, which can be dissociated into H+ and OH-

14. 10.3.3 Distinguish between alkanes and alkenes using bromine water. Bromine water (a red liquid) tests for unsaturated hydrocarbons (alkenes) Alkanes (cyclohexane) → stay yellow/orange no reaction Alkenes (cyclohexene) → turn clear / colourless because of reaction with unsaturated hydrocarbon

15. 10.3.3 Distinguish between alkanes and alkenes using bromine water. The Fuse School: https://www.youtube.com/watch?v=1r9aYS4Nd ac&list=PLW0gavSzhMlReKGMVfUt6YuNQsO 0bqSMV&index=84 https://www.youtube.com/watch?v=1r9aYS4Nd ac&list=PLW0gavSzhMlReKGMVfUt6YuNQsO 0bqSMV&index=84 http://www.youtube.com/watch?v=NjIuBvod2e Mhttp://www.youtube.com/watch?v=NjIuBvod2e M

16. 10.3.4 Outline the polymerization of alkenes.

17. 10.3.4 Reactions of Alkenes: Polymerization Mono- = one -mer = part Poly- = many So if several monomers are connected (think Lego’s), you get a … ???

18. 10.3.4 Reactions of Alkenes: Polymerization Naming polymers: put “poly-” in front of the name of the monomer There are 3 polymerization mechanisms that you need to be familiar with: 1. Polyethene 2. Polychloroethene 3. Polypropene

19. 10.3.4 Reactions of Alkenes: Polymerization: Polyethene Monomer: ethene (aka ethylene), CH 2 =CH 2 Conditions: Temp: 200º C Pressure: 2000 atm Initiator: O 2

20. Polyethene Undergoes additions reactions with itself to make a chain n CH 2 =CH 2  [-CH 2 -CH 2 -] n

21. 10.3.4 Reactions of Alkenes: Polymerization: Polychloroethene Each chloroethene contains 1 chlorine Therefore when the chloroethene molecules polymerize, every other carbon will bond to 1 chlorine This is PVC

23. 10.3.4 Reactions of Alkenes: Polymerization: Polypropene +=+=

24. 10.3.4 Reactions of Alkenes: Polymerization: Types Addition: All of the examples we’ve seen are classified as “Addition Polymerization” vs. Condensation The Fuse School: https://www.youtube.com/watch?v=nz1ucI6gCIg&list=PL W0gavSzhMlReKGMVfUt6YuNQsO0bqSMV&index=3

25. 10.3.4 Reactions of Alkenes: A Hint Draw the structure of your alkene so that the C=C is in the middle and the other parts bond above and below the carbons. For example. A polymer of but-2-ene should look like: = +

26. 10.3.4 Reactions of Alkenes: Practice Draw the structure for 7 units of Poly-2-chloropropene.

27. 10.3.4 Reactions of Alkenes: Reaction Type Definitions Addition: Bromination: Dehydration: Hydration: Hydrogenation:

28. 10.3.5 Outline the economic importance of the reactions of alkenes.

29. 10.3.5 Uses of alkene products Ethene can be used for a variety of purposes: Steam → ethanol Polymerize → polyethene React with chlorine → chloroethene… which interacts with ethanol → PVC React with benzene → phenylethene (styrene)… which interacts with ethanol → polystyrene

30. Outline the economic importance of the reactions of alkenes (10.3.5) Making margarine Hydrogenation (addition of H) of vegetable oils (alkenes)

31. Making ethanol Ethene + water Alcoholic beverages or use as fuel

32. Making plastics Teflon Tetrafluoroethene PVC Polychloroethene

33. Teflon non-stick pans