In Praise of Isomers

For the past two weeks I have been working hard to finish Chemistry 11. With just one more unit to go, my mission is almost complete. En route, however, isomers have given me a bit of a bumpy ride.

To understand isomers, you have to know that a hydrocarbon is a molecule composed of only carbon and hydrogen atoms. You write it as CH4. The 4 after the H means that there are four hydrogens bonded to the carbon. Keep in mind there are many kinds of hydrocarbons other than CH4, such as C9H20. Fun stuff, huh?

Now you need to know a little bit about carbon and hydrogen:

• Carbon has four electrons in its outer shell. A full outer shell has eight electrons, meaning carbon has to bond with four other atoms to fill its shell and be happy.
• Hydrogen has one electron in its outer shell but needs two to be happy. (Don't we all?)
• Electrons float around atoms in a shell––two in the first shell, eight in the second and third shells and 18 in the fourth.
• So if one hydrogen bonds with one carbon, the hydrogen will be happy but the carbon will still have three spots to fill, which it usually fills with hydrogen.

This is why CH4 is the simplest hydrocarbon. There are not many ways you can restructure this molecule. But take C3H8. You can write out all the carbon atoms in one line, with the hydrogens surrounding the carbons. But you can also put one of the carbons below the other carbon atoms. This is a different molecule from all three carbons in a straight line. And it has a different name. Welcome to the mathematical world of isomers.

Once you get to molecules such as C9H20 there are many different isomers. A Chemistry 11 requirement is that you have to be able to figure out all the isomers, draw them and name them. Which can be exhausting. I hope that if isomers make an appearance on the test, they will be easier molecules or we'll be told how many isomers there are.

This link explains isomers in a more detailed and clearer way than I can manage just now.