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most places you can find crude oil were once sea beds. Crude oils
vary in color, from clear to tar-black, and in viscosity, from water
to almost solid.
Crude oils are such a useful starting point for so many
different substances because they contain hydrocarbons.
Hydrocarbons are molecules that contain hydrogen and carbon and
come in various lengths and structures, from straight chains to
branching chains to rings.
There are two things that make hydrocarbons exciting to
chemists:
— Hydrocarbons contain a lot of energy. Many of the things
derived from crude oil like gasoline, diesel fuel, paraffin wax and
so on take advantage of this energy.
— Hydrocarbons can take on many different forms. The
smallest hydrocarbon is methane (CH 4), which is a gas that is a
lighter than air. Longer chains with 5 or more carbons are liquids.
Very long chains are solids like wax or tar. By chemically cross-
linking hydrocarbon chains you can get everything from synthetic
rubber to nylon to the plastic in tupperware. Hydrocarbon chains
are very versatile!
The major classes of hydrocarbons in crude oils include:
— Paraffins general formula: C nH 2n+2 (n is a whole number,
usually from 1 to 20) straight- or branched-chain molecules can be
gasses or liquids at room temperature depending upon the
molecule examples: methane, ethane, propane, butane, isobutane,
pentane, hexane;
— Aromatics general formula: C 6H 5 –Y (Y is a longer,
straight molecule that connects to the benzene ring) ringed
structures with one or more rings rings contain six carbon atoms,
with alternating double and single bonds between the carbons
typically liquids, examples: benzene, napthalene;
Napthenes or Cycloalkanes general formula: C nH 2n (n is a
whole number usually from 1 to 20) ringed structures with one or
more rings that contain only single bonds between the carbon

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