Carbon

Carbon is a chemical element with the symbol C and atomic number 6. It is nonmetallic and can form up to four covalent bonds, making it very versatile. Carbon has been known since ancient times and makes up about 0.025 percent of Earth's crust. 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.

Carbon is important because it is a key part of all known life. It is the second most abundant element in the human body by mass, making up about 18.5% of our bodies. The atoms of carbon can bond together in many different ways, creating various forms called allotropes, such as graphite, diamond, amorphous carbon, and fullerenes. These forms have very different properties; for example, graphite is soft and can be used for writing, while diamond is the hardest natural material known.

Carbon can form a huge number of compounds, with about two hundred million already described. This ability to form many compounds is why carbon is central to chemistry and life on Earth. It is found in many places, including limestones, dolomites, carbon dioxide, coal, oil, and even deep under the ocean in methane clathrates.

Characteristics

Carbon can be found in several different forms, called allotropes. Two common ones are graphite, which is soft and slippery, and diamond, which is the hardest natural substance. These differences come from how the carbon atoms are arranged.

Carbon is very good at forming stable connections, or chemical bonds, with many elements, especially other carbon atoms. This helps create millions of different chemicals. Carbon also has a very high point at which it turns from solid to gas, called sublimation.

In its gaseous form, carbon can appear as diatomic carbon, which glows green when excited. Liquid carbon is a dark, shiny liquid that needs very high temperatures and pressures to exist. Carbon’s electrons give it unique properties, like how easily it bonds with other atoms.

Occurrence

Carbon is the fourth most abundant chemical element in the observable universe by mass after hydrogen, helium, and oxygen. It is found in the Sun, stars, comets, and the atmospheres of most planets. Some meteorites contain tiny diamonds formed when the Solar System was still developing.

In 2014, NASA updated a database to track polycyclic aromatic hydrocarbons (PAHs) in space. These complex carbon and hydrogen compounds may have played a role in the formation of life. They were formed a few billion years after the Big Bang and are found throughout the universe, near new stars and exoplanets.

On Earth, carbon is found in many places. It makes up about 12% of carbonate rocks like limestone, dolomite, and marble. It is also in fossil fuels such as coal, petroleum, and natural gas, and in methane hydrates in polar regions and under the oceans. Carbon moves through the environment in a process called the carbon cycle. Plants take in carbon dioxide from the air or water and use it to grow. Animals eat plants or other animals and release carbon dioxide when they breathe out. Some carbon ends up in oceans, and some becomes fossil fuels over millions of years.

Formation in stars

Main articles: Triple-alpha process and CNO cycle

Carbon is created inside giant and supergiant stars through a process called the triple-alpha process. This process needs three helium nuclei to collide at the same time. It happens in stars where temperatures are very high. When large stars end their lives in explosions called supernovas, they scatter carbon into space. This carbon becomes part of new stars and planets. Our Solar System has plenty of carbon, which is important for life as we know it.

The CNO cycle is another way stars produce energy, using carbon as a helper in combining hydrogen.

Carbon cycle

On Earth, the total amount of carbon stays about the same. It moves between different places in a cycle. Plants take in carbon dioxide from the air or water to grow through a process called photosynthesis. Animals eat plants or other animals and release carbon dioxide when they breathe out. Some carbon dissolves in oceans. Over long periods, dead plants and animals can turn into fossil fuels like coal and oil, which release carbon when burned.

Compounds

Carbon is special because it can form long chains of bonds with itself. These strong bonds let carbon create many different compounds. Most compounds in the world contain carbon.

The simplest carbon molecules are called hydrocarbons. These are made of hydrogen atoms attached to a chain of carbon atoms. By adding other atoms like oxygen or nitrogen, carbon can form many important molecules. For example, with oxygen and hydrogen, carbon helps make sugars and fats. With nitrogen, it forms important compounds like DNA, which carries the instructions for life.

Carbon also forms many minerals and other useful materials. One common compound is carbon dioxide, which we breathe out and which helps plants grow. Another is carbon monoxide, which is produced when there isn’t enough oxygen to burn something completely. Carbon also teams up with metals to make very strong materials used in many tools and machines.

History and etymology

The word "carbon" comes from the Latin word carbo, meaning coal or charcoal. Many languages have similar words for carbon, often related to coal. People have known about carbon for thousands of years in the form of soot and charcoal. Diamonds were found as early as 2500 BCE in China.

Important discoveries about carbon were made over time. In 1722, a scientist showed that carbon helps turn iron into steel. In 1772, another scientist proved that diamonds are a type of carbon. Later, scientists found that graphite, once thought to be lead, is also carbon mixed with a little iron. In 1985, scientists discovered a new form of carbon called fullerene, which includes interesting shapes like buckyballs and nanotubes. These discoveries helped scientists learn more about carbon and its different forms.

Main article: allotrope

Production

Main article: Graphite

Main article: Diamond

Graphite is a form of carbon found in many places, such as China, India, Brazil, and North Korea. It forms in certain types of rocks and can be turned into pencil leads by crushing the rock and separating the graphite. There are three types of natural graphite: amorphous, flake, and vein. Amorphous graphite is the most common and least expensive. Flake graphite is rarer and more valuable, used in products like flame retardants. Vein graphite is the rarest and most valuable type.

Diamonds are another form of carbon found deep within the Earth. Most diamonds come from a few places, like Russia, Botswana, Australia, and the Democratic Republic of Congo. Diamonds are found in rocks and separated using special tools. In the past, diamonds were mainly found in India, but now they come from many countries. Scientists can also make diamonds in labs using high pressure and temperature or other methods.

Applications

Carbon has many important uses in our everyday lives. It is a key part of all living things, and we need it to survive. We find carbon in fuels like methane gas and crude oil, which are used to make many products such as gasoline and plastics.

Carbon is also used in many other ways. Graphite, a form of carbon, is what makes the "lead" in pencils. It is also used in electrodes, electric motors, and as a lubricant. Charcoal, another form of carbon, is used for drawing, grilling food, and in some industrial processes. Diamonds, which are made of carbon, are used in jewelry and also in tools for cutting and drilling because they are very hard. Carbon fiber, which is strong and lightweight, is used to make things like sports equipment and aircraft parts.

Precautions

Pure carbon, like graphite or charcoal, is not harmful to humans and can be handled safely. However, inhaling too much coal dust or soot can irritate the lungs and cause health problems. Diamond dust can also be dangerous if inhaled or swallowed.

Carbon can burn very brightly when there is enough air and high temperatures. Large piles of coal that have been stored for a very long time can sometimes catch fire suddenly when exposed to air.