2. This is ethane, an alkane. Halogens alkane are based on alkane but with one or more of the H atoms replaced by a halogen atom.

3. This is a general structure for a halogenoalkane with one halogen atom, represented by an X.

4. This is a general structure for a halogenoalkane with one halogen atom, represented by an X.

5. The halogen atoms involved are fluorine, chlorine, bromine or iodine.

6. Fluoroalkanes contain fluorine. This is fluoroethane.

7. Chloroalkanes contain chlorine. This is chloroethane.

8. Bromoalkanes contain bromine. This is bromoethane.

9. Iodoalkanes contain iodine. This is iodoethane.

10. Halogenoalkanes are named after the alkane upon which they are based, called the parent alkane.

11. The names of halogenoalkanes with methane as their parent alkane all end in methane.

12. If there is one bromine atom, we get bromomethane.

13. If there are two bromine atoms, we get dibromomethane.

14. If there are three bromine atoms, we get tribromomethane.

15. If there are four bromine atoms, we get tetrabromomethane. Notice that the name ends in 'methane' even though there are no hydrogen atoms at all.

16. Halogenoalkanes with two or more carbon atoms can have position isomers.

17. The carbon atoms are numbered to distinguish the different isomers.

18. The lowest possible numbers are used in the name, so in this case we number from the right.

19. The bromine atom is on carbon 1, so the name begins 1-bromo.

20. There are three carbon atoms, so it is 1-bromopropane.

21. In this isomer the bromine atom is on carbon 2, so the name begins 2-bromo.

22. There are three carbon atoms, so it is 2-bromopropane.

23. This halogenoalkane has two bromine atoms.

24. The carbon atoms are numbered so that we can name it.

25. There is a bromine atom on carbon 1, so the name begins 1.

26. There is another bromine atom on carbon 1, so the name begins 1,1.

27. There are two bromine atoms, so the name begins 1,1-dibromo.

28. There are three carbon atoms, so this halogenoalkane is called 1,1-dibromopropane.

29. This halogenoalkane also has two bromine atoms.

30. There is a bromine atom on carbon 1, so the name begins 1.

31. There is a bromine atom on carbon 2, so the name begins 1,2.

32. There are two bromine atoms, so the name begins 1,2-dibromo.

33. There are three carbon atoms, so this halogenoalkane is called 1,2-dibromopropane.

34. This is chlorobutane with its chlorine atom on one of the end carbon atoms.

35. We use the lowest numbers, so this is 1-chlorobutane.

36. This is chlorobutane with its chlorine atom on one of the middle carbon atoms.

37. We use the lowest number, so this is 2-chlorobutane.

38. There is a branched isomer of chlorobutane. The longest chain has three carbon atoms, so we name it after propane.

39. It is 1-chloromethylpropane.

40. There is a branched isomer.

41. This one is 2-chloromethylpropane.

42. If the carbon atom carrying the halogen atom is directly attached to one other carbon atom, we have a primary halogenoalkane.

43. If the carbon atom carrying the halogen atom is directly attached to two other carbon atoms, we have a secondary halogenoalkane.

44. If the carbon atom carrying the halogen atom is directly attached to three other carbon atoms, we have a tertiary halogenoalkane.

46. The molecular formula shows how many of each type of atom are present in 1-iodopropane.

47. The structural formula shows how the atoms are bonded together in 1-iodopropane.

48. The displayed formula shows all the atoms and all the bonds in 1-iodopropane.

49. The skeletal formula shows the iodine atom but leaves out the carbon atom and other hydrogen atoms.

50. The molecular formula shows how many of each type of atom are present in 2-iodopropane.

51. The structural formula shows how the atoms are bonded together in 2-iodopropane.

52. The displayed formula shows all the atoms and all the bonds in 2-iodopropane.

53. The skeletal formula shows the iodine atom but leaves out the carbon atom and other hydrogen atoms.

54. This halogenoalkane has a bromine atom and a chlorine atom.

55. There is a bromine atom on carbon 1, so the name begins 1-bromo.

56. There is a chlorine atom on carbon 2, so the name begins 1-bromo-2-chloro.

57. There are three carbon atoms, so this halogenoalkane is called 1-bromo-2-chloropropane.

58. Where there are two different halogens in a halogenoalkane, the halogens are named in alphabetical order and not in numerical order.

59. There is a bromine atom on carbon 2, so the name begins 2-bromo.

60. There is a chlorine atom on carbon 1, so the name begins 2-bromo-1-chloro.

61. There are three carbon atoms, so this halogenoalkane is called 2-bromo-1-chloropropane.