This document describes the properties of alkenes. Alkenes are unsaturated hydrocarbons that contain carbon-carbon double bonds. They undergo addition reactions at the double bond, such as hydrogenation to form alkanes. Common reactions include addition of hydrogen, halogens, water, and oxidation. Alkenes polymerize to form polymers by joining many monomer units. Alkenes are more reactive than alkanes due to the presence of the double bond.

1. ALKENE

3. CCAtom carbon2, 4Atom carbon2, 4

4. CCAtom carbon2, 4Atom carbon2, 4

5. CCAtom carbon2, 6Atom carbon2, 6

6. HAtom hydrogen1CCAtom carbon2, 6Atom carbon2, 6

7. HAtom hydrogen2CCAtom carbon2, 7Atom carbon2, 6

8. HHAtom hydrogen2CCAtom carbon2, 7Atom carbon2, 6

9. HHAtom hydrogen2CCAtom carbon2, 8Atom carbon2, 6

10. HHHAtom hydrogen2CCAtom carbon2, 8Atom carbon2, 6

11. HHHAtom hydrogen2CCAtom carbon2, 8Atom carbon2, 7

12. HHHHAtom hydrogen2CCAtom carbon2, 8Atom carbon2, 7

13. HHHHAtom hydrogen2CCAtom carbon2, 8Atom carbon2, 8

14. It is classified as unsaturated hydrocarbons.(An unsaturated hydrocarbon contains at least one double covalent bonds between carbon atoms).Alkenes are hydrocarbons with the general formula :CnH2n where n = 2, 3, ……, ∞Every alkene has a carbon-carbon double covalent bond, C = C in its molecule.

15. HHHCCHExample : Formation of an ethene molecule(a) Ethene, C2H4HHCCHH Structural formula for ethane, C2H4The first member of alkenes has two carbon atoms in a molecule because ……………………. bond is formed between two carbon atoms.double

16. Naming of AlkenesThe name of straight chain alkenes are also made up of two component parts :(i) Stem/root : indicates the number of carbon atoms in the longest continuous carbon chain.The names of stems for the first nine straight alkanes are :eth, prop, but, pent, hex, hept, oct, non anddec(ii) Suffix/ ending : indicates the group of the compound.For alkene, the suffix is ‘ene’ because it belongs to the alkene group.

17. 4.Naming of Alkenesa) Naming the straight chainalkene :(i) Determine the longest carbon chain containing double bond.give the stem name according to the number of carbon atoms ; eth, prop, but, pent, hex, hept, oct, non anddec(ii) Add the suffix “ene” at the end of the name.(iii) Number the carbon atoms from the end nearer to the double bond and give the double bond the smaller number.

18. .Activity 6 :-Complete the table below :5.Physical properties of Alkenes are similar to alkanes

19. Activity 7 :-Complete the following table :

20. Physical state at room temperature (25 OC) :Ethene, propene and but-1-ene are …………………..Pent-1-ene to non-1-ene are ………………….. and dec-1-ene is …………………..Alkenes have ………………….. melting and boiling points because the ………………….. van deer Waals forces (intermolecular forces) between small molecules need ……………… amount of heat energy to overcome the forces.

21. As the number of carbon atoms per molecule increases, the molecular size of alkene …………………., the ………………….. the intermolecular forces, more ………………….. energy is needed to ………………….. this forces, the melting and boiling points …………………..gasliquidsolidLow weakLow increasesStronger overcomeHeat increases

22. 6.Chemical properties of Alkenesmore(a) Alkenes are chemically ………………….. reactive than alkanes because of the existence of double covalent bond between two carbon atoms.Almost all of the chemical reactions of alkene occur at the double bond.(b) The chemical reactions of alkenes are :I : Combustion ReactionAlkene burns completely in the excess oxygen to produce ……………………. and ……………Alkene + O2 -> CO2 + H2O Carbon dioxidewater

23. Activity 8 :-1.Balance the following equations :C2H4 + O2 -> CO2 + H2OC3H6 + O2 -> CO2 + H2OC4H8 + O2 -> CO2 + H2O2.Write the balanced equation for combustion reaction of :Pentene:………………………………………………………Hexene:………………………………………………………Octene:…………………………………………………………

24. However, alkene burns incompletely (in limited supply of oxygen) to form carbon dioxide, carbon monoxide, carbon (in the form of soot) and water.Example : 2C2H4+ 3O2 2C + 2CO + 2H2OorC2H4+ 2O22CO + 2H2O

26. Addition reactionII : Addition ReactionAs alkenes are unsaturated hydrocarbon, they undergo addition reaction.An addition reaction is a reaction in which other atoms are added to each carbon atom of the ……………….. bond, [C = C ] to form ……………….. covalent bond product [ C - C ].double Single C = C + XY C CXY (unsaturated) (saturated )

28. Simple molecules like hydrogen, H2 ; hydrogen chloride, HCl ; water, H2O or halogens, [F2, Cl2, Br2, I2] can be added to the double bond. (i) Addition of Hydrogen (Hydrogenation)Alkenes react with hydrogen at 180 Cin the presence of nickel/platinum as a catalyst to produce alkanes.

29. Hydrogenation is used to prepare an alkane (saturated compound) from an alkene (unsaturated compound) in industry.Example : Ni / Pt180 CEthene Ethane+ H2

31. (ii) Addition of Halogen (Halogenation)Alkenes react with halogens such as chlorine,Cl2 and bromine, Br2 at room conditions.(nocatalystorultraviolet light needed)Example : + Br2Ethene (bromine water) When ethene gas is passed through bromine water, brown colour of bromine water is decolourised // colourless solution formed.

32. This reaction is used to distiguish a saturated hydrocarbon and unsaturated hydrocarbon. 1,2-dibromoethane

33. C2H4 gasBromine water(nocatalystorultraviolet light needed)

34. beforeafteralkeneAlkane

35. Which is alkene?

37. iii)Addition of Hydrogen Halide [ HX HCl, HBr, HI ]Alkenes react with hydrogen halide such as hydrogen chloride, HCl or hydrogen bromide, HBr at room temperature to form haloalkane.Example : C2H4 + HCl -> C2H5Cl Ethene Hydrogen chloride Chloroethane C3H6 + HBr -> PropeneHydrogen bromide ………………….

38. Activity 9 :-Complete the equation and draw the structural formulae for all the reactants and products in the equation below :1 (a) C3H6 + H2 -> C3H8 (b) C4H8 + H2 -> ………. (c) ………. + H2 -> C6H142 (a) C3H6 + Br2 -> C3H6Br2(b) C4H8 + Cl2 -> ………. (c) ………. + I2 -> C6H12I2

39. iv)Addition of Oxidizing agent : (Oxidation reaction)Acidified Potassium manganate(VII), KMnO4 solution

40. AcidifiedPotassium dichroromate(VI), K2Cr2O7 solution

41. In this reaction, two hydroxyl, -OH groups are added to the carbon-carbon …………………… in an alkene molecule.

42. An alkene…………………… the ………………… colour of acidified potassium manganate(VII)solution //the orangesolution of acidified Potassium dicrhoromate(VI), K2Cr2O7turns to ……………………This reaction is used to distiguish a …………………… hydrocarbon and …………………… hydrocarbondouble bondDecolorized purplegreensaturatedunsaturated

43. Example :KMnO4(aq)[Purple]AlkeneColourlessKMnO4C2H6 gasC2H4 + H2O + [O] -> C2H4(OH)2Ethene Ethan-1,2-diolcolourless

44. Activity10 :-Propan-1,2-diolEthan-1,2-diol☺Complete the following equation :(a) C3H6 + H2O + [O] -> C3H6(OH)2H H(b) H C = C H + H2O + [O] ->HHHHCCOHOH

45. KMnO4

46. v)Addition of Water (Hydration)Alkenes react with water (in the form ofsteam) at high temperature and pressure in the presence of phosphoric acid as a catalyst to produce alchohols.H3PO4300 C / 60 atmAlkene + H2O AlcoholExample :C2H4 + H2O C2H5OH EtheneethanolH3PO4300 C / 60 atm

47. alkenealcohol

49. Activity 11 :-☺Complete the following equation H3PO4300 C / 60 atmC3H6 + H2O H3PO4300 C / 60 atm+H20

50. Addition of steam to alkene is one way to manufacture alcohol in industry H3PO4300 C / 60 atmCnH2n + H2O(g) CnH2n+1OH Alcohol AlkeneExample :C4H8 + H2O H3PO4300 C / 60 atmButene

51. vi)Addition Polymerisation reactionIn this reaction, small alkene molecules undergo addition reaction at a high pressure of 1000 atm and temperature of 200 C. Thousands of alkene molecule join together to form long chain giant molecules called …………………………

52. The smallrepeating units of molecules that join together to form polymer are called …………………………polymermonomernEthenePolythene