The Chemistry of Carbon

There are more compounds composed of carbon than any other element. Since carbon is always found in organic (living) compounds, the chemistry of carbon is referred to as organic chemistry. Carbon is the key element in plastics, synthetic fibers, foods, medicines, and all petroleum products. Petroleum products are composed of hydrogen and carbon and are called hydrocarbons. The oil used to make petroleum products came from once living things that died long ago. So petroleum is considered organic chemistry because the oil which made the petroleum products came from once living things. The only carbon compounds that do not exist in living things are carbon monoxide and carbon dioxide. These two are the only carbon compounds which are not considered organic.

Carbon forms so many compounds because it has four valence electrons. Carbon has an atomic number of six. Therefore, it has two electrons in its first energy shell and four in its outer energy shell. Since carbon wants eight electrons in its outer energy shell, it has the potential to form four covalent bonds with other carbon atoms or with different atoms. The valence electron configuration of carbon allows it to bond chemically with almost all other elements.

Carbons often bond with hydrogen to form hydrocarbons. Hydrocarbons are compounds which contain only hydrogen and carbon. The simplest hydrocarbon is methane. Methane is CH4. Other hydrocarbons are: ethane--C2H6, propane--C3H6, butane--C4H10, pentane--C5H12, hexane--C6H14, heptane--C7H16, octane--C8H18, nonane--C9H20, decane--C10H22. All of these are the alkane series. The alkane series consists of hydrocarbons which have only a single covalent bond between the carbon atoms which form the backbone of the compound. The alkane series all have names which end in "ane."

In these hydrocarbons, the carbon atoms form the backbone of the molecule. The hydrocarbons with a short backbone consisting of 1-5 carbons are gases. Those having 6-20 carbon backbones are liquid. Those having above 20 carbons tend to be solids such as waxes and asphalt.

Because carbons can link with each other in so many different ways, carbon compound exist in many isomers. Isomers are compounds with the same molecular formula, but different structural formulas. Molecular formulas show the number and kind of atoms which form the molecule. Structural formulas show how these atoms are arranged in the molecule. Butane and methyl propane are hydrocarbons which are isomers of each other. The molecular formula for both is C4H10.

In a saturated hydrocarbon, the carbon backbone is formed of carbons which share a single pair of electrons. These are called single bonds. However, carbons can bond to each other by sharing more than one pair of electrons. The hydrocarbons that have one or more double or triple bonds are called unsaturated hydrocarbons.

Hydrocarbons with at least one double bond between the carbon atoms are called the alkene series. All alkenes have a name ending in "ene." An example is ethylene (C2H4). The prefix "poly" means many. So polyethylene is many ethylenes linked together.

Many different compounds can be made from hydrocarbons by replacing one of the hydrogens with a different functional group. A functional group is an atom or a group of atoms that replaces one or more hydrogens in a hydrocarbon. An example of a functional group is the hydroxyl ion (OH-). When the hydroxyl ion replaces one of the hydrogens in a hydrocarbon, it forms an alcohol.

The alkyne series of hydrocarbons have at least one triple bond between the carbons. An example is propyne, a gas often used by welders.

The organic compounds which are most important to living things are carbohydrates. Carbohydrates are composed of carbon, hydrogen and oxygen, and include sugars, starch and cellulose. The carbohydrates are used by living things for energy. The main carbohydrate used by animals to produce energy is glucose--C6H12O6. Fructose, a sugar found in plants is an isomer of glucose. Therefore its molecular formula is also C6H12O6. Table sugar is called sucrose and is produced from sugar cane. Its molecular formula is C12H22O11. Starch is a long chain of sugar molecules used by plants to store energy. Starch is converted to glucose when needed. Animals store energy as glycogen (animal starch) and fat.

Two other important organic compounds are fats (lipids) and protein. Carbohydrates do not contain an organic acid. Fats and protein do contain an organic acid. If the carbon backbone of a fat is composed of carbons bonded to each other with single bonds, each carbon can be saturated with hydrogens. This is a saturated fat. If there are some double bonds between the carbons forming the backbone of the fat, the carbons cannot be saturated with hydrogens, and it is an unsaturated fat. If there are a lot of these double bonds, it is a polyunsaturated fat. Polyunsaturated fats are better foods than saturated fats.

Proteins are polymers of amino acids. Amino acids are composed of an organic acid, plus the amine group (NH4).

Carbon Study Sheet