Halogen Substitution Groups 
The group seven elements, the halogens, are very reactive. They will, if given the chance, displace H from the carbon chain and take its place. When in place they take on special prefix names; fluorine becomes fluoro, chlorine becomes chloro, bromine becomes bromo and iodine becomes iodo.
 
          H                              H
           |                                |
eg. H-C-H + Cl2 ----->  H-C-Cl + HCl
           |                                |
          H                              H
 
Dupont and Anachem were the leading manufacturers of a special class of halocarbon compounds called Freon's. A partial list follows and you should try drawing two or three of them to get familiar with them.
Trade Name Molecular Formula IUPAC Name
Freon 11 CCl3F trichloro-fluoromethane
Freon 12 CCl2F dichloro-difluoromethane
Freon 13 CClF3 chloro-trifluoromethane
Freon 14 CF4  tetrachloromethane
Freon 22 CHClF2 chloro-difluoromethane
Freon 23 CHF trifluoromethane
Freon 113 C2Cl3F3 1,1,2-trichloro-1,2,2-trifluoroethane
Freon 114 C2Cl2F 1,2-dichloro-1,1,2,2-tetrafluoroethane
Freon 142b C2H3ClF3 1-chloro-1,1-difluoroethane
Freon 13b1 CBrF3 bromo-trifluoromethane
Freon 318 C4F8 octafluoro-cyclobutane