Hydrocarbons and Organic Chemistry

With everything else we're learning in chemistry, we won't have time to delve into the beautiful world of organic chemistry much. Organic chemistry involves the molecules associated with living things. Because of their carbon backbones (in most cases) they make great geometric shapes. We will be learning the most basic hydrocarbons in this class.

Hydrocarbons have two parts - hydrogen and carbon. One carbon can make four bonds. If the maximum number of bonds are used, we say that it's saturated. If there are double or triple bonds, the molecule is unsaturated. We'll be learning the first ten basic hydrocarbons, making models of two, and learning the rules for naming the unsaturated hydrocarbons.

Saturated hydrocarbons (no double or triple bonds) are called alkanes. Here are the first ten alkanes.
  1. methane
  2. ethane
  3. propane
  4. butane
  5. pentane
  1. hexane
  2. heptane
  3. octane
  4. nonane
  5. decane

Learning the names is pretty easy, once you get past the first four. Methane is the most basic. This is a natural gas and is found in biological gasses as well. (That's a nice way to say "farts.") Meth and eth go together. When I think propane (and propane accessories) I think of three. Perhaps I relate it to a family of three or three pro-fessional athletes on a pedestal, but pro is three. And butane is four. That's the liquid/gas in lighters. People light cigarettes with lighters. Cigarettes leave butts. Butt-ane... Butane. Ok, that was horrible, but memorable. All of the others go back to their Latin prefixes, so they're easy.

If one of these has a double bond, we don't call them alkanes, but alkenes. And that double bond will change the name of the substance. Ethane (C2H6), when it gets a double bond between the carbons, it loses two hydrogens and we now have ethene, or ethylene (C2H4). Propane (C3H8), when receiving a double bond, becomes propene (C3H6), or propylene. This is true of all hydrocarbons with double bonds.

     Can you figure out why there is no methene?

Sometimes, hydrocarbons can form triple bonds. These are alkynes. (They're alphabetical A, E, Y.) If ethane (C2H6) has a triple bond between the carbons, it will lose four hydrogens and ethyne (C2H2) is formed. Any time you see the y in there, you'll have a triple bond. Propyne, butyne, octyne and decyne are other examples of alkynes.

The more you play with hydrocarbons, the more you realize that their models make pretty pictures. The most common models you'll see for simple hydrocarbons are "stick and ball" models. Often the elements will be represented by balls or junctions, and the bonds are represented by sticks. We will be making models for methane and ethane in class using marshmallows and toothpicks. If you miss this exercise, make models at home wout of anything and bring them in to be checked. This is the first taste of chemical geometry the students will have. If you'd like a clearer 3-D rendering of the molecules, click on their pictures.

If this is something you like, I invite you to explore more examples of organic models. Learn some basic combinations. For example, if you replace a hydrogen with a hydroxyl group (-OH) you've made alcohol. Methane becomes methanol, or wood alcohol. Ethane becomes ethanol - the kind of alcohol in some beverages. If you stick the -OH on propane you have propanol, and if you stick it on the middle carbon, you have isopropyl alcohol - or rubbing alcohol.

Speaking of rearranging, when you rearrange a molecule, you create an isomer. Without getting into too much detail, let's say that isomers are molecules that got a little rearranged. It's easier to see than to explain, so I've provided a couple pictures for you. Notice how both of these examples show molecules with the same ingredients, but the parts are found in different places.
There are tons of things that can be learned by studying organic molecules. If you like this kind of thing, I suggest you practice learning the names and shapes and wow your future chemistry teachers.