Allotropes of carbon

Carbon is a versatile element capable of forming many different structures. These different forms are known as allotropes. An allotrope is a structurally different form of the same element. Carbon can do this because of its valency, which is its ability to form four chemical bonds. This unique property allows carbon atoms to arrange themselves in many ways. Scientists use the Samara Carbon Allotrope Database (SACADA) to track these forms. Currently, about 500 hypothetical 3-periodic allotropes are known.

One of the most famous allotropes is diamond. In a diamond, each carbon atom is covalently bonded to four other carbons. This creates a tetrahedral geometry, which is a three-dimensional shape. These tetrahedrons form a network of six-membered carbon rings. This specific structure is called a face-centered cubic lattice. Because the bonds are unstrained, the resulting network is extremely strong. This makes diamond the hardest known natural mineral.

Because of its hardness, diamond is used for many industrial tasks. It is an excellent abrasive for cutting and grinding. Engineers use diamond in drill bits, saw blades, and polishing tools. Many diamonds are not used for jewelry but for these heavy-duty jobs. About 80% of mined diamonds are unsuitable for gemstones. This amount equals roughly 100 million carats or 20 tonnes every year. Additionally, humans produce 400 million carats of synthetic diamonds annually.

Graphite is another very common allotrope of carbon. It was named by Abraham Gottlob Werner in 1789. The name comes from the Greek word for "to draw" or "to write." Unlike diamond, graphite is an electrical conductor. This is because each carbon atom uses only three of its four outer electrons for bonding. This leaves one electron per atom to move freely in a delocalized system. These electrons can move throughout the planes of the carbon layers.

Graphite has many different uses due to its stability. It is the most stable form of carbon under standard conditions. Because it is heat-resistant, it is used in nuclear reactors and crucibles. Some forms of graphite are used in reentry shields for missile nosecones. Other types are used in fire seals around doors. These are called intumescent graphites. During a fire, they expand and char to block heat and fumes.

Scientists have also discovered much smaller, specialized structures. In 1985, researchers discovered buckminsterfullerenes, often called "buckyballs." These molecules are shaped like hollow spheres or tubes. They resemble the geodesic structures designed by Richard Buckminster Fuller. There is also graphene, which is a single layer of graphite. Graphene has extraordinary electrical and thermal properties. Researchers are studying if it can replace silicon in electronic devices.

Other unusual forms of carbon exist in extreme environments. Lonsdaleite, or hexagonal diamond, forms when meteorites hit the Earth. The massive heat and pressure transform graphite into this denser form. Carbon can also be found in space as diatomic carbon. This is often detected in comets and certain stars using spectroscopy. Finally, there is amorphous carbon, which has no long-range atomic pattern. This includes common substances like soot and coal.