Carbon

A chemical element with symbol C and atomic number 6

Carbon is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds. Carbon is a member of group 14 of the periodic table. It is the 15th most abundant element in the Earth's crust and the fourth most abundant element in the universe by mass, after hydrogen, helium, and oxygen.

Properties

Carbon is known for its ability to form a vast number of compounds, more than any other element, with almost ten million compounds described to date. This vast number of compounds is due to carbon's ability to form stable bonds with other carbon atoms, as well as with atoms of other elements.

Allotropes

Carbon is known to exist in several different forms, known as allotropes. The most well-known allotropes of carbon are diamond, graphite, and fullerenes.

• Diamond is a transparent crystal that is the hardest naturally occurring material known. It is used in cutting tools and jewelry.
• Graphite is opaque and black, and it is used in pencils and as a lubricant.
• Fullerenes are molecules composed entirely of carbon, taking the form of a hollow sphere, ellipsoid, or tube. Buckminsterfullerene is a well-known example.

Diamond (left) and graphite (right) are two allotropes of carbon.

Isotopes

Carbon has two stable, naturally occurring isotopes: carbon-12 and carbon-13. Carbon-12 is the most abundant, making up about 98.9% of carbon on Earth. Carbon-14 is a radioactive isotope of carbon, used in radiocarbon dating to determine the age of carbonaceous materials up to about 60,000 years old.

Occurrence

Carbon is found in all known life forms and is the second most abundant element in the human body by mass, after oxygen. It is a major component of biomolecules such as proteins, lipids, nucleic acids, and carbohydrates.

In the Earth

Carbon is found in the Earth's crust in the form of carbonates in minerals such as limestone and dolomite, and in organic deposits such as coal, peat, oil, and natural gas.

In the atmosphere

Carbon is present in the Earth's atmosphere primarily as carbon dioxide (CO_), a greenhouse gas that is a major contributor to global warming.

Uses

Carbon is used in a wide variety of applications due to its versatility and abundance.

• Industrial uses: Carbon is used in the form of graphite for high-temperature crucibles, as a lubricant, and in pencils. Diamond is used in cutting, grinding, and drilling tools.
• Chemical industry: Carbon is a key component in the production of steel, where it is used to control the hardness and strength of the alloy.
• Energy: Carbon-based fuels such as coal, oil, and natural gas are major sources of energy worldwide.

Biological Role

Carbon is essential to all known life. It is the backbone of organic chemistry, forming the basis of DNA, RNA, and proteins. The carbon cycle is a fundamental part of the Earth's ecosystem, involving the exchange of carbon between the atmosphere, oceans, soil, and living organisms.

Related pages

• Carbon cycle
• Organic chemistry
• Carbon footprint
• Carbon dioxide