Carbon is an element with symbol C and atomic number 6. As it is a member of group 14 on the periodic table, it is nonmetallic and tetravalent .i.e. has four electrons free to form covalent chemical bonds. There are three isotopes that occur in nature, with 12C and 13C being stable, while 14C is radioactive, decaying with a half-life of about 5730Â years. The English name carbon comes from the Latin "carbo" which means "burnt wood".
Carbon is an element of prehistoric discovery and was known in the forms of soot and charcoal to the earliest human civilizations. Charcoal was prepared around Roman times by the same chemistry as it is at present, by heating wood in a pyramid covered with clay to exclude air. Today, the best known allotropes of carbon are Diamond and Graphite. Diamonds were probably known as early as 2500Â BCE in China.
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It is very widely spread in nature, for example; in the sun, stars, comets, and atmospheres of most planets. It is also found in some meteorites in the form of microscopic diamonds.
Carbon is the fifteenth most occurring element in the Earth's crust and fourth in the universe by mass after hydrogen, helium, and oxygen. It exists in all known life forms, and is the second most abundant element by mass after oxygen in the human body.
Pure carbon has a very short-life; therefore, carbon is stabilized in a variety of multi-atomic structures with different molecular configurations called allotropes. Amorphous carbon, graphite, and diamond are the three best-known allotropes of Carbon.
The physical properties of carbon vary widely with the allotropic form. For example, diamond is known to be the hardest substance that occurs in nature, whereas graphite is one of the softest substances known.
Diamond is highly transparent, while graphite is opaque and black. Diamond is not a very good electrical conductor, while graphite has a very high electrical conductivity.
Under normal conditions, diamond has the highest thermal conductivity of all known materials. All the allotropic forms are solids under normal conditions but graphite is the most thermodynamically stable.
Carbon can form both Organic as well as Inorganic Compounds. Along with the uniqueness of carbon in its pure form, it is also interesting in other forms. It shows its capability to serve as a connecting block in a branch of chemistry that we refer to as "Organic Chemistry" that is mainly about Organic Compounds of Carbon.
As the name suggests, Organic Chemistry is a branch of chemistry that focuses on the chemistry of life. It is also about the chemistry required to produce solvents, fuels, pharmaceuticals, plastics, refrigerants, lubricants etc.
One of the properties that give rise to carbon's uniqueness is its aptitude to create four covalent bonds allowing it to connect to itself in order to produce carbon chains of different lengths and configurations, or to link to non-carbon atoms to form compounds with unique and special chemical properties. The chain-forming property of Carbon is known as Catenation.
Hydrogen has a special position in Organic Chemistry. Wherever a Carbon atom bonds with a hydrogen atom, the carbon chain ends. This particular association between carbon and hydrogen is so significant that it leads to a sub-class of chemicals known as "Hydrocarbons" which consists of compounds made up of only Hydrogen and Carbon atoms.
Factors that affect the characteristics and properties of organic molecules the most are Chain length, side chains and functional groups of the molecule.
Carbon is present in all known organic life and is the base of organic chemistry. Carbon forms many groups of essential biological compounds like sugars, lignins, chitins, alcohols and fats when combined with Oxygen and Hydrogen. On addition of nitrogen, it forms alkaloids, and on adding sulfur also, it forms antibiotics, amino acids, and rubber products. With the addition of phosphorus to these other elements, it forms DNA and RNA [the chemical-code carriers of life] and adenosine triphosphate (ATP) [the most important energy-transfer molecule in all living cells].
Carbon is a nutrient of great significance in the body, and is therefore greatly required. The fact that every part of the body has and needs large amounts of this element is a proof of its significance. It is used as a building block for several complex and vital life processes. It is the carbon in our bodies that brings the various atoms inside the body together, and makes them execute actions that help growth, in a unified way.
Formation of Organic Compounds:
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Carbon requires 8 electrons to complete its valence shell. Therefore, it forms 4 bonds with other atoms (each bond consists of one of the bonding atom's electrons and one of carbon's). All valence electrons participate in bonding. These bonds form a tetrahedron, as illustrated below:
Carbon forms four bonds
Organic chemicals get their variety from the various ways carbon bonds to other atoms. The simplest of organic chemicals, known as hydrocarbons, contain only carbon and hydrogen atoms; the simplest hydrocarbon (named methane) consists of a single carbon atom which is bonded to 4 hydrogen atoms:
Methane-a Carbon atom bonded to four Hydrogen atoms
But carbon can bond to other carbon atoms in addition to hydrogen:
Ethane- a Carbon-Carbon bond
It can bond to itself in many different ways.
Carbon atoms can form:
Hexane-a 6-Carbon chain
Isohexane-a branched Carbon chain
Cyclohexane-a ringed Hydrocarbon
To add to the complications of organic chemistry, along with single carbon-carbon bonds, carbon atoms can also form double and triple bonds with each other:
Single Bonding Double Bonding Triple Bonding
Alkanes are the first set of simple hydrocarbons and consist only of carbon-carbon single bonds. The alkanes are named by adding with the root ending "ane", a prefix that describes the number of carbon atoms in the molecule.
The chemical formula for all alkanes is given by the expression CnH2n+2. The structural formula of a compound shows each carbon atom and the elements that are attached to it.
The second class of simple hydrocarbons, the alkenes, consists of molecules that contain at least one double-bonded carbon pair. Alkenes follow the same naming rule used for alkanes. A prefix (the number of carbon atoms) is combined with the ending "ene" that denotes an alkene.
Ethene, for example is the two-carbon molecule that has one double bond. The chemical formula for the simple alkenes follows the expression CnH2n. As one of the carbon pairs is double bonded, simple alkenes have two fewer hydrogen atoms than alkanes.
Applications and Uses:
Carbon in its various forms has a numerous uses, a few of which are:
The lead in lead pencils is formed by mixing graphite with clay.
Diamonds are used in jewellery, as an abrasive for mechanical grinding and mining as well as for cutting tools.
"Soot" or carbon black is used as a material for light absorption.
Coal, which is a form of carbon, is used as a fuel for heating, transportation and for generating electricity.
Hydrocarbons are mainly derived from crude oil from fossil fuels, they are developed from their raw form to be used as fuels and lubricants, and as the base for manufacturing organic chemicals which are used in the plastic and pharmaceutical industries.
Graphite powder is used as a dry lubricant in machinery.