Now, I don't pretend to understand molecular bonds, but a scientist once explained how refrigerants are made this way. He said that each carbon atom can bond to four other atoms. So, methane (natural gas) is made up of single carbon atoms, which are each bonded to four hydrogen atoms. And to make R-12, for example, they strip the hydrogen atoms off of each carbon atom and bond four chlorine atoms in their place. This makes the solvent, carbon tetrachloride.
The next step is to strip two chlorine atoms off of each carbon tetrachloride molecule and replace them with fluorine atoms. So, the end product (R-12) is made up of single carbon atoms that are bonded to two chlorine and two fluorine atoms.