Matter & Energy

Matter is composed of atoms or groups of atoms called molecules. The arrangement of particles in a material depends on the physical state of the substance. In a solid, particles form a compact structure that resists flow. Particles in a liquid have more energy than those in a solid. They can flow past one another, but they remain close. Particles in a gas have the most energy. They move rapidly and are separated from one another by relatively large distances.


Carbon, nonmetallic chemical element, known by the symbol C, that is the fundamental building block of material in living organisms and is important to many industries. Carbon occurs in nature in nearly pure form in diamond and graphite. It is also the major component of coal, petroleum, asphalt, limestone, and most materials made by plants and animals. The name carbon is derived from the Latin word carbo, meaning charcoal, a material that is composed primarily of carbon.

A carbon atom can chemically combine with atoms of other elements, as well as with other carbon atoms, to form molecules. Molecules that contain two or more elements make up compounds. Carbon can form more compounds than can any other element except hydrogen.

Carbon is present in all substances known as organic compounds (see Organic Chemistry). Originally, scientists used the term organic compounds for materials that could only be obtained from living or dead organisms. Today chemists consider nearly any compound that contains carbon to be organic, whether they obtain it from organisms or synthesize it in a laboratory or in factories. Compounds that do not contain carbon are called inorganic compounds.

Carbon atoms form part or all of the backbone for the major molecules of all living things on Earth, including sugars, proteins, fats, and deoxyribonucleic acids (DNA), the molecules that carry the genetic code of living organisms. Many of the materials that we use in everyday life contain carbon-rich organic compounds. For instance, we wear clothing made of organic compounds—either natural fibers, such as wool, silk, or cotton; or synthetic ones, such as nylon or polyester. We construct our houses and furnishings from organic materials, such as wood and plastics. We burn carbon-rich fossil fuels, including gasoline, natural gas, and coal, for heat and energy. In addition, we use organic compounds as pesticides and medicines, and the foods we eat are carbon compounds.


Scientists use the carbon atom as the basic unit of mass and as a clue to the age of an object. Industries use carbon to make steel from iron, purify metals, and add strength to rubber. In the form of diamond, carbon can cut most other substances and shine more brilliantly in jewelry than most other gems. Carbon compounds can be burned as fuel to heat food or homes, as well as form many different molecules for all sorts of human needs.

Carbon has many industrial uses. At high temperatures, carbon combines with iron to make steel. The chemical composition of steel determines its physical properties. Carbon steel with about 1.5 percent carbon is used to make sheet steel and tools. Steel used for automobile and aircraft engine parts contains about 1 percent carbon. High strength steel used for transportation equipment and structural beams contains about 0.25 percent carbon. Stainless steel for engine parts or kitchen utensils contains from 0.03 to 1.2 percent carbon. Carbon, in the form of coke, can also react with tin oxide and lead oxide to yield the pure metals tin and lead. Carbon black, made of fine particles of amorphous carbon, is produced by incomplete combustion of natural gas. It is mainly used as a filler and reinforcing agent for rubber.

Natural and synthetic diamonds can cut nearly every other known material. Gem cutters, surgeons, and manufacturers use diamond knives and drills. General Electric Company produced the first synthetic diamond in 1955. Today tiny synthetic diamonds are commonly used as abrasives. Producers of metal tools use lasers to heat carbon dioxide over a metal surface, making the carbon atoms coat the surface with a diamond film. This diamond coating can make cutting tools last much longer than untreated tools.

People burn fossil fuels to generate energy. Burning, or combustion, is the reaction of a substance with oxygen to produce new substances and energy (in the form of heat). When coal burns, carbon reacts with oxygen to yield carbon dioxide and heat. The higher the carbon content, the greater the energy released in combustion. Therefore, anthracite (containing the most carbon) is the most valuable coal, and lignite (containing the least amount of carbon) is the least valuable. In petroleum, oil, and natural gas, burning releases energy when bonds between the atoms break and when carbon and hydrogen atoms recombine with oxygen to form carbon dioxide and water.

Carbon compounds are the basis of the synthetic organic chemicals, which account for many of the products of the chemical industry. Pharmaceuticals, pesticides, paints, and coatings are among the products made from synthetic organic chemicals. The synthetic fiber, synthetic rubber, and plastics industries depend upon the unique ability of carbon to form stable, long chains, or polymers, made from small organic molecules bonded together. Carbon-based polymers form synthetic fibers, such as nylon, rayon, and polyester. All the plastics, from polyethylene terephthalate (PET) in soft drink bottles to polyvinyl chloride (PVC) in window frames to styrene in car parts, depend on the properties of carbon.