Hydrocarbon

Hydrocarbons are obtained by refining petroleum at refineries such as this one.

A hydrocarbon is any chemical compound that is constituted of just the elements carbon (C) and hydrogen (H). Each hydrocarbon molecule consists of a carbon backbone, or "carbon skeleton," with hydrogen atoms attached to that backbone.

Hydrocarbons are among the Earth's most important natural resources. They are currently the main source of the world’s electric energy and heat energy (such as for heating buildings) because they produce large amounts of heat when burned. The gasoline that serves as fuel for automobiles consists primarily of hydrocarbons. In addition, many hydrocarbons are useful as starting materials for the synthesis of commercial products such as plastics.

Natural occurrence and extraction

Hydrocarbons are the main constituents of petroleum (literally, "rock oil"), also called "oil," and natural gas. They are commonly found in and extracted from the Earth´s subsurface. Petroleum is a mixture of liquid hydrocarbons, and natural gas is mainly constituted of methane gas.

The extraction of liquid hydrocarbon fuel from a number of sedimentary basins has been integral to modern energy development. Hydrocarbons are mined from tar sands and oil shale. These reserves require distillation and upgrading to produce synthetic crude and petroleum. A future source of methane may be methane hydrates found on ocean floors.

Types of hydrocarbons

A model of the alkane known as hexane.

A model of the alkyne called ethyne.

A model of an arene called benzene.

There are essentially three types of hydrocarbons:

1. Saturated hydrocarbons, also known as alkanes: In each molecule of an alkane, the chemical bonds that join the carbon atoms are single covalent bonds. If the alkane molecule includes a ring of carbon atoms (all connected by single covalent bonds), it is called a cycloalkane.
2. Unsaturated hydrocarbons, which are subdivided into two groups:
   • alkenes: Each molecule of an alkene contains at least one double covalent bond between carbon atoms.
   • alkynes: Each molecule of an alkyne contains at least one triple covalent bond between carbon atoms.
3. Aromatic hydrocarbons, or arenes: Each molecule of an aromatic hydrocarbon contains at least one aromatic ring, in which the bonds between carbon atoms are aromatic bonds.

Some simple hydrocarbons

The simplest hydrocarbon is methane, the main constituent of natural gas. Its chemical formula, CH₄, indicates that each molecule of methane consists of four hydrogen atoms attached to one carbon atom. Ethane, with the formula C₂H₆, is a hydrocarbon (more specifically, an alkane) in which each molecule has two carbon atoms held together with a single covalent bond, and three hydrogen atoms are bound to each carbon atom. Each molecule of propane (C₃H₈) has three carbon atoms, and each molecule of butane (C₄H₁₀) has four carbons.

General chemical formulas

If a hydrocarbon molecule contains "n" carbon atoms, and the type of hydrocarbon is known, its general chemical formula can be written as follows:

• Alkane: C_nH_2n+2.
• Cycloalkane: C_nH_2n (assuming a single ring, with all the carbon atoms in the ring structure).
• Alkene: C_nH_2n (assuming only one double bond in each molecule).
• Alkyne: C_nH_2n-2 (assuming only one triple bond in each molecule).
• Aromatic ring: C_nH_n (assuming a single ring, with all the carbon atoms in the ring structure).

The above chemical formulas are based on the understanding that each carbon atom forms four covalent bonds, including bonds with hydrogen atoms and other carbon atoms. A double covalent bond counts as two bonds; a triple covalent bond counts as three bonds. A carbon atom in an aromatic ring is a special case and can have only one hydrogen atom attached to it.

Molecular graph

A "molecular graph" of a hydrocarbon is a simple representation of the carbon skeleton of the molecule under consideration. Each line in the molecular graph represents a covalent bond that connects two carbon atoms. Thus, although the graph shows no symbols for carbon atoms, a carbon atom is (by convention) located at each end of each line. The symbols for hydrogen atoms are not shown either, but each carbon atom holds as many hydrogen atoms as it needs to form four covalent bonds.

Uses of hydrocarbons

Most hydrocarbons are combustible. When burned, they produce carbon dioxide, water, and large quantities of heat. We rely on this energy to heat our homes and other buildings and to generate electricity. When heating a home, for example, oil or natural gas is burned and the energy released is used to heat water or air. The hot water or air is then circulated around the building.

A similar principle is used to create electric energy in power plants. A hydrocarbon fuel (such as natural gas) is burned, the energy released is used to convert water into steam, and the steam is used to drive turbines that generate electricity.

Hydrocarbons are also raw materials that serve as a feedstock for the production of a wide range of organic chemicals, which in turn are used for such commercial products as plastics, solvents,

Hydrocarbons are constituents of the major fossil fuels (coal, petroleum, natural gas, etc.) and biofuels, as well as plastics, paraffin, waxes, solvents and oils.

Effects on health and the environment

The concentration of hydrocarbon vapors can be harmful if inhaled.

In urban pollution, hydrocarbons, along with nitrogen oxides and sunlight, contribute to the formation of ozone in the troposphere.

In an ideal reaction, the waste would be only water and carbon dioxide but because the coal is not pure or clean there are often many toxic byproducts such as mercury and arsenic. Also, incomplete combustion causes the production of carbon monoxide which is toxic because it will bind with hemoglobin more readily than oxygen, so if it is breathed in, oxygen can not be absorbed, causing suffocation. Incomplete combustion also has a byproduct of carbon in the form of soot.

Coal reserves will last for decades and possibly beyond 2100. Mostly in response to climate concerns, clean coal technology is currently under development. For example, the UK and China have signed an agreement to develop such technology with carbon dioxide emissions capture and storage in both China and the EU by 2020. Similar research is being conducted in the United States and other countries. By some, hydrocarbons in the atmosphere are considered to be dangerous air pollutants.

External links

• The Methane Molecule
• Dismissal of the Claims of a Biological Connection for Natural Petroleum.
• Poten & Partners: Glossary of Hydrocarbon Terms

See also

• Abiogenic petroleum origin
• Energy storage
• Fractional distillation
• Functional group
• Alkanes

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