Historia

Crude oil is the term for "unprocessed" oil, the stuff that comes out of the ground. It is also known aspetroleum. Crude oil is a fossil fuel, meaning that it was made naturally from decaying plantsand animals living in ancient seas millions of years ago -- 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 toalmost solid.
Crude oils are such a useful starting point for so many different substances because they containhydrocarbons. Hydrocarbons are molecules that contain hydrogen and carbon and come invarious 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 ofthe 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 hydrocarbonis methane (CH4), 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 youcan 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 generalformula: CnH2n+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: C6H5 - Y (Y is a longer, straight molecule that connects to the benzene ring) ringed structures with one or more ringsrings contain six carbon atoms, with alternating double and single bonds between the carbons typically liquids examples: benzene, napthalene
* Napthenes or Cycloalkanes general formula: CnH2n (n is...