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Carbon

What is carbon?

Carbon is a nonmetallic chemical element of group-14 (IVA) in the periodic table with atomic number 6 and symbol C. It occurs in nature as carbon black, activated carbon, graphite, diamond, carbon dioxide, carbon monoxide, carbonates, etc. Carbon is the key chemical element for all living organisms present in our environment. It forms a large number of organic compounds with hydrogen.

Activated and black carbon occurrence, properties, isolation and uses

The electronic configuration of carbon is 1s2 2s2 2p2. Therefore, it has four valence electrons which use for chemical bonding purposes. In most cases, it formed four single covalent bonds. The four single covalent bonds are equivalent and formed by sp3 hybridization.

Interestingly, sp3 hybridization is not the only way to attain noble gas configuration. Carbon can attain octet through multiple covalent bonding with its own atom by sp2 or sp hybridization. It also formed multiple bonds with oxygen, nitrogen, or sulfur.

The chemistry of carbon is unique due to its catenation properties. The strength of C-C single bonds and C-C multiple bonds helps carbon to form long-chain organic compounds. The property of forming compounds with chains of identical atoms is called catenation.

What is carbon cycle?

It is the biogeochemical cycle where carbon and its compounds are exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of our earth’s environment. Major steps of the carbon cycle may include,

  1. CO2 and water in our environment are worked up by plants through the agency of chlorophyll and sunlight to form carbohydrates.
  2. Some plants are taken by the animal and carbon may be bio-accumulated into their bodies.
  3. When these animals and plants die, carbon may be released back into our atmosphere.
  4. Some of these carbon present in dead plants or animals may be stored as coal or petroleum (fossil fuels).
  5. It releases carbon dioxide into the atmosphere when fossil fuels are burned.

Properties of carbon

The chemistry of group-14 elements followed by their electronic configuration but differences in properties between carbon and silicon are rather wide.

Carbon
Symbol C
Discovery Prehistoric
Name derived from derived from the Latin word carbo meaning charcoal
Main allotropes Diamond, graphite
Common isotopes 6C12, 6C13, 6C14
Crystal structure Graphite Diamond
Simple hexagonal (black) Face-centered cubic crystal lattice (clear)
Periodic properties
Atomic number 6
Electron per shell 2, 4
Atomic weight 12.011
Electronic configuration [He] 2s2 2p2
Group 14
Period 2
Block p-block
Physical properties
State at 20 °C Solid
Sublimation point 3825 °C, 6917 °F, 4098 K
Triple point 4600 K, ​10,800 kPa
Density (g cm−3) Diamond Graphite
3.513 2.267
Chemical properties
Atomic radius (non-bonded) 1.70 Å
Covalent radius 0.75 Å
Oxidation number or states 4, 3, 2, 1, 0, -1, – 2, -3, -4
Ionization energy (kJ mol−1) 1st 2nd 3rd
1086.45 2352.63 4620.47
Electron affinity 121.766 kJ mol−1
Electronegativity 2.55 (Pauling scale)
Molar heat capacity
(J mol−1 K−1)
Diamond Graphite
6.155 8.517
CAS number 7440-44-0

Interesting facts about carbon

  • It has the ability to create multiple bonds with other carbon atoms and oxygen, nitrogen, or sulfur atom.
  • It forms negative anions in beryllium carbide (BeC2), sodium alkyls (NaCH3), and alkali metal carbides (Na2C2).
  • The electronegativity difference between carbon and fluorine is not sufficient to induce ionic character in fluorocarbon.
  • It has the properties of catenation. Therefore, it forms long-chain organic compounds.

Carbon in periodic table

Carbon is placed in group 14 of the periodic table along with silicon, germanium, tin, and lead. All these elements have an outermost quantum shell composition of s2p2.

Position of nonmetal chemical element carbon in periodic table

Sources of carbon

It is present in the earth’s crust to the extent of about 0.08 percent and crude oil, coal, and natural gas. Hydrocarbon is the most common combined form of carbon. Flakes of graphite and crystalline diamond occur in metamorphosed sedimentary rocks like quartz.

Diamond occurs in Kimberlite (a dark color basic rock of Kimberlin found in South Africa) with ancient volcanic pipes. India and Borneo are the oldest diamond-producing countries in the world. The allotrope diamond was found in Brazil in 1729 and South African deposits were discovered in the latter part of the nineteenth century.

Isotopes of carbon

The principal isotope of carbon is C-12. The isotope, C-13 occurs in nature to the extent of 1.11 percent. It can be used in Fourier transform nuclear magnetic resonance (NMR-spectrum) data analysis.

The atmospheric CO2 contains about 1.2 × 10−10 percent of radioactive C-14 isotope with a half-life of 5570 years. It is produced by the neutron-proton reaction on nitrogen by thermal neutrons resulting from cosmic radiation. The ratio of C-14 and C-12 is used widely in radiocarbon dating or determination of age of plants or animals.

Allotropes of carbon

Atomic carbon is a very short-lived species and stabilized by various multi-atomic structures which known as allotropes. It has several crystalline allotropic firms. Diamond and graphite are common allotropic forms of carbon. Other poorly understood allotropes are,

  • β-graphite
  • Amorphous carbon
  • Lonsdaleite or hexagonal diamond
  • Chaoite (very rare mineral)
  • Fullerenes (Buckyballs)

Carbon compounds

Carbon is the key element in all living systems. It forms more organic and inorganic compounds than any other chemical element except hydrogen.

The chemistry of carbon compounds can be explains by their electronic configuration. It has atomic number 6 with electronic configuration 1s2 2s2 2p2. Therefore, four electrons are present in the outer quantum orbital.

When we have taken four ionization energies together, the value is very high. No compounds know with + 4 cations. Instead of forming ionic compounds, in most cases, the compound is formed by four covalent bonding with sp3 hybridization.

It not only forms the single covalent bonding to attain the noble gas electronic configuration. It also formed multiple bonds with sp2 and sp-hybridization in unsaturated hydrocarbon compounds like ethylene and acetylene.

Naturally, it possesses the + 4 oxidation number or state due to the very low electronegativity but in metal carbides like sodium carbides or calcium carbides, it possesses a − 1 oxidation state.

The common oxidation state of carbon in various inorganic compounds is +4 but the +2 state is also found in carbon monoxide and transition metal carbonyl complexes.

Production process

Production of coke

Among all the natural forms, coke is used in large quantities for energy generation in our daily life. Coke is obtained by cooking or high-temperature carbonization of coal in the absence of air.

Production of graphite

Natural graphite was obtained in a mixture of mica, quartz, and silicates. The mixture was washed by flotation and heated with hydrochloric acid and hydrofluoric acid in a vacuum. The residual silicon compounds precipitated as SiF4 molecules.

Nearly half of the industrial requirement of graphite is made by the synthetic process. It is made by heating silica with coke in an electric furnace at 2500 °C for about 24 hours.
SiO2 + 3 C → SiC + 2 CO + C (graphite) + Si

Production of diamond

Natural diamond is mined in large quantities which are about 18 tonnes per year. Of these 30% are used as gems while rest goes to various industries.

Only small-size industrial diamonds are made synthetically by subjecting graphite to 125000 atm pressure and 3000 K temperature. But if we use the metal chemical catalyst, the conversion is achieved at 70,000 atm pressure and 2000 K temperature.

Carbon black

It is prepared by incomplete thermodynamics combustion of hydrocarbons.

Activated charcoal

Activated charcoal is prepared by controlling pyrolysis of organic compounds like sawdust or coconut shell. Activation of the surface is accompanied by adding materials that oxidize or dehydrate the organic substrate on the surface. The edge of the hexagonal graphite sheets is probably covered with oxygenated groups which are responsible for surface activity.

Graphite fibers

Graphite fibers are obtained when synthetic fibers or asphaltic fibers are subjected to pyrolysis. The strong fibers have the same structural formula as graphite but they contain layers of ribbons in place of sheets. It is parallel to the axis of fibers.

The strong bonds in a plane are responsible for high tensile strength. Graphite fibers are used mainly for making tennis rackets, aircraft components, etc.

Uses of carbon

The first two elements in group 14 occupy a special position in our life. They use widely in our daily life in various production processes.

  • Hydrocarbon is the major economic form of carbon that occurs in nature as fossil fuels like methane gas and crude oil or petroleum. Crude oil is used for the production of gasoline, petrol, diesel, kerosene, and many other petrochemical products.
  • Cellulose is a carbon-containing polymer obtained from plants. It is used for making wool, cotton, and linen. It is also maintaining the structure of plants.
  • Plastics are synthetic polymers of carbon. It is used widely in our daily life.
  • The allotrope coke is vital in the extraction of iron and many other metals.

Uses of graphite and diamond

Graphites and diamonds are two major allotropic forms of carbon.

  • Graphite is used mainly in steelmaking, metal foundries, refractories, making crucibles, nozzles, fuel cell electrodes, etc.
  • It is used for making lubricants.
  • It is also used in brake lining, pencils, brushes for electric motors, etc.
  • Graphite is used as a neutron moderator in nuclear power reactors.

The useable diamonds are classified into two classes, gem-grade diamonds, and industrial-grade diamonds. About 80% of mined diamonds are unsuitable for making gemstones. Therefore, they are relegated to industrial use.

  • Like gold or platinum, gem-grade diamonds is a valuable gemstone.
  • Industrially, diamond is used mainly for cutting, drilling, grinding, and polishing.

Uses of carbon black

  • Carbon black is largely used in the rubber industry to increase the strength of rubbers. These rubbers are used particularly for making car tires and plastic compounds.
  • It is a black pigment that uses widely in printing ink, carbon paper, automotive finishes, and laser printer toner.

Uses of activated charcoal

  • Activated charcoal is a very efficient absorbent used for absorbing organic pollutants from drinking water and greenhouse gases from the air.
  • It is largely used as a decolorizing agent in the sugar industry.
  • In medicinal chemistry, activated charcoal is used to absorb toxins, poisons, or gases from the digestive system.
  • It is used in gas purification systems, including air pollution and gas masks.
  • Activated carbon is used as a chemical catalyst in the sewage water pollution system.