This unit is called Hydrocarbons. It is an introduction to what used to be called "organic chemistry", the chemistry of living things. In our current technological culture it is considered "the chemistry of carbon" and covers everything from natural gas and other fossil fuels to plastics and polymers. If you tried to list all the different ways that carbon compounds are involved in human activity you would compile a very long list indeed.

The first part of this unit explains what hydrocarbons are, and how they are arranged. As chemicals (but then, what isn’t?) hydrocarbons are subject to typical chemical reactions. You may also want to revise covalent bonding before proceeding.

Some Historical Comments

Way back when, after earth, air, fire and water, but before the scientific method, alchemists tried to make gold out of lead and other common metals. They never succeeded. The scientific method elbowed its way onto the philosophical scene and chemistry, vaguely as we know it, was born. Over time chemists divided chemistry in two. On one hand you had chemicals of the earth; salts, metals and metal ores, things from the ground. On the other hand you had the chemistry of living things. The later was referred to as "organic" (living) chemistry. The former became "inorganic". There didn’t seem to be a practical way to get organic products from inorganic reactants, nor the other way ‘round. In fact, for a long while it was commonly supposed that the two were necessarily separate. Not only had they not found a way, but no way existed, because organic compounds all contained a mysterious élan vital, a life force, which could not be synthesised in a beaker. Then a troublesome German chemist by the name of Wöhler convincingly converted ammonium cyanate (can you work out its formula?), an inorganic compound, to urea (H₂NCONH₂), most definitely an organic compound, and another great theory was out the window. Such is the scientific method.

The real point of all this is that organic compounds were different from inorganic ones. Apart from being found in living things, organic compounds are fragile. Heat them up, they decompose. Inorganic compounds (as a rule) aren’t fussed by a bit of heat. Raise the temperature of a chunk of your local dolerite to a hundred degrees and it will hardly notice, but raise the temperature of egg albumin to a hundred degrees and you’ve got a boiled egg and there’s no way to unboil it. A further point in all this is that organic compounds (as a rule) are either plain or modified hydrocarbons. Hydrocarbons are molecules (covalent bonds, remember?) comprised only of the elements hydrogen and carbon, hence the name. Modified hydrocarbons are plain hydrocarbons that have had oxygen, nitrogen, sulfur, a halide, or some combination thereof added to them.

Carbon is special

Carbon is a most unique element. It is the only element capable of making long chains of itself by means of covalent bonds. This may be the chief reason why it is the backbone of all living things.

Once the water is removed from you, you are, by weight, far and away mostly carbon. Carbon chains are the basic structure of fats, carbohydrates and proteins. Without the ability to form these chains, there would be no life.

Carbon is found in the middle of the second row in the Periodic Table.  A carbon atom has six electrons, two in the inner layer and four in the next.  Thus carbon has four valence electrons.  With this number, carbon is unlikely to either gain or lose four electrons to make a complete shell, so carbon is prone to form covalent bonds with other non-metals. As it has four electrons in its outermost energy level, it can make up to four bonds.