Carbon is a chemical element with symbol C and atomic number 6. It is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table.
History and Discovery
The discovery of carbon dates to prehistoric times and was used by ancient human civilizations as in the form of charcoal and coal. Diamonds were discovered in China in around 2500BCE. The name carbon has been derived from the word carbo (Latin for coal and charcoal). Carbon was discovered as a novel element by 1722 by Antoine Ferchault de Réaumur, who proposed that this novel element can be used to transform iron into steel. Later in 1786, A. Vandermonde, Claude Louis Berthollet, and Gaspard Monge confirmed that graphite was a form of carbon in the same way as diamond (discovered earlier in 1772) .
|Periodic Table Classification||Group 14
|State at 20C||Solid|
|Electron Configuration||[He] 2s2 2p2|
|Electron Shell||2, 4|
|Density||2.26 g.cm-3 at 20°C|
|Atomic Mass||12.01 g.mol -1|
|Electronegativity according to Pauling||2.55|
Carbon is characterized as the 4th most abundant element in the universe and the 15th most abundant element in the Earth’s crust. Biologically, carbon holds a significant position and is part of all living systems. In humans, carbon makes about 18.5% of body mass and is the second most abundant element in the body . Atomic form of carbon is very short lived and readily stabilizes in multi-atomic configurations. Carbon exists in various forms, termed as allotropes (variation in bonding of carbon atoms due to its valency). The common allotropes of carbon include diamond, graphite, amorphous carbon (charcoal and carbon black) and nanoforms of carbon including graphene and fullerenes . Carbon is major hydrocarbons present in fossil fuels including coal, natural gas, and crude oil. Carbon is also present in stars and sun and in the atmosphere of many planets. Natural reserves of diamond are present in Canada, Congo, Russia and South Africa.
The different allotropic forms of carbon have different physical properties. Graphite is black, opaque and extremely soft, while crystal is highly transparent and is the hardest natural element. The electrical conductivity of graphite is very good as compared to diamond, which is an outstanding electrical insulator . Carbon and its allotropes have the highest thermal conductivities as compared to all elements. Elemental carbon is insoluble in water, organic solvents and acids and bases. Graphite is the most thermodynamically stable allotrope of carbon at standard temperature and pressure. All allotropes of carbon are solid under standard conditions. Carbon and its allotropes are resistant to melting at atmospheric pressure and remain solid at considerably high temperature. Mostly, the oxidation state of carbon is +4 (in inorganic compounds) and +2 in organic compounds. Carbon has the ability to sublime (ability to transform directly from solid to gas state at high temperature) and have the highest sublimation point. The density of graphite and diamond are 2.25 g/cm³ and 3.51 g/cm³, respectively .
Carbon is quite reactive and forms about one million different compounds, and there is a significant increase in their number each year. Graphite is more reactive than diamond. Carbon is quite resistant to oxidation by strongest oxidizers at normal conditions. At higher temperatures, however, carbon forms carbon oxides by reacting with oxygen, which is an exothermic reaction. There are three oxides of carbons: carbon suboxide (C3O2), carbon dioxide (CO2) and carbon monoxide (CO). Carbon can form carbides by reacting with certain metals at high temperatures, such as tungsten carbide. Fluorine is the only halogen gas that can react with carbon in elemental form .
Significance and Uses
- Graphite is widely used in refractory applications and making greasy lubricants .
- Graphite is used in making furnace lining, carbon brushes in motors.
- Activated carbon or charcoal is used in making filters for respirators and kitchen hoods.
- Diamond is used in making drills and cutter for cutting rocks and other hard material, due to its immense strength and durability.
- Carbon fiber is used in making fishing rods, tennis rackets, airplanes as it is extraordinarily strong and light weight.
- Carbon has revolutionized nanotechnology by the discovery of carbon nanotubes, that are widely used in electronic industry.
- Carbon is widely used in carbonated and fuzzy drinks.
- It is used in various metallurgy processes.
- Carbon black is used in making pigments and inks.
- Carbon dioxide is used in fire extinguishers and as dry ice.
The increased atmospheric concentration of carbon has become a major health and environmental challenge. And carbon oxides (CO2 and CO) are characterized as the major contributors of Global warming. About 2 decades ago, the natural concentration of CO2 in the Earth’s atmosphere was around 280 ppm and has increased to 390 ppm (in 2013) due to human activities, such as burning of fossil fuels with oxygen. The natural concentration of atmospheric carbon dioxide controls a certain phenomenon known as greenhouse effects, which allows visible light to escape the Earth’s atmosphere but prevents some infrared rays from escaping. This leads to an increase in the atmospheric heat and temperature, which naturally helps in sustaining the life on Earth. But a considerable increase in the greenhouse, due to a anthropogenic emission of CO2 have become a global challenge and is bringing an unprecedented climatic change that can affect the natural balance of life . Carbon is characterized as low toxicity metal. Inhalation of carbon black can lead to damage of lungs, but it is an occupational hazard. Certain compounds of carbon are also toxic, including cyanide and carbon monoxide.
Isotopes of Carbon
There are three naturally occurring isotopes of carbon, 12C and 13C (stable isotopes), while 14C is a radionuclide, that have a half-life of about 5,730 years. Carbon-12 is the most abundant, with a natural abundance of 98.93. Carbon-14 is only present in trace amount on Earth and is mostly present in the atmosphere, where it is formed from the interaction of cosmic rays and nitrogen .
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