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Carbon and its Compounds

Why Carbon forms Covalent Bonding?

We know that a majority of substances used by us daily, from paper and plastics to coal and petrol, are all made up of carbon. Food grains, pulses, medicines, cotton, synthetic fibres, wood etc. are all made up of carbon. Carbon is also a major part of all living things. In air, it is present as carbon dioxide and comprises around 0.03% of the total air.

Let us study about carbon and its bonding in its compound in more detail.

Carbon is a non-metal having the symbol ‘C’ and atomic number six. Since the atomic number of carbon is six, its electronic configuration is 2, 4. This means that carbon contains two electrons in K shell and 4 electrons in L shell (outermost shell). Hence, it has four electrons in its valence shell.

Since carbon has four electrons in its valence shell, it needs four more electrons to complete its octet. Therefore, it is a tetravalent element.

In order to complete its octet i.e., to attain its noble gas configuration and to stabilize itself, carbon can:

  • Either lose four electrons to form C4+ or gain four electrons to form C4. This, however, requires a lot of energy and would make the system unstable.
Therefore, carbon completes its octet by sharing its four electrons with the other carbon atoms or with atoms of other elements.

The bonds that are formed by sharing electrons are known as covalent bonds. Covalently bonded molecules have weak intermolecular forces, but intramolecular forces are strong.

Carbon has four valence electrons and needs four more electrons to complete its octet. Therefore, it is capable of bonding with four other atoms of carbon or atoms of other elements having a valency of 1.

For example, the molecule, methane can be formed with hydrogen (H) atoms that have only one electron in its K shell. To attain the noble gas configuration, it combines with four hydrogen atoms as shown in the figure.

Now, let us study the properties of carbon compounds.

  • Covalent bonds are made by atoms by sharing their electrons. Formation of ions does not take place in this process. In addition, these compounds do not have any extra electrons. Hence, covalent compounds are non- conductors of electricity.


  • As all organic compounds contain covalent bonds, they also have low melting and boiling points. This becomes evident from the following data.


Melting point (K)

Boiling point (K)

Acetic acid












Also, from the above data, it can be inferred that the forces of attraction between the carbon molecules in carbon compounds is not very strong.

Because of their low melting and boiling points, these compounds mostly exist as liquids or gases at room temperature.

  • Board question(s) related to this lesson:

Carbon is the versatile element present in food, clothes, medicines, papers, etc. In addition, all living structures are carbon based. The earth’s crust has only 0.02% carbon in the form of minerals and the atmosphere has 0.03% carbon dioxide. In spite of the small amount of carbon available in nature, the importance of carbon is immense.

Position of carbon in the periodic table

Carbon has an atomic number 6 and an atomic mass as 12 u. It contains 2 and 4 electrons in the K and L shell respectively. It belongs to the group IVA of the periodic table and has a valency of 4.

Occurrence: Carbon occurs in free as well as in combined state.

In free state, carbon occurs as diamond, graphite, and coal. Diamond and graphite are pure forms of carbon while coal is an impure form of carbon in which the percentage of carbon varies from 24% to 90%.

In combined state, carbon occurs in

  • bio-molecules such as cellulose, carbohydrates, fats, proteins, etc.

  • minerals in the form of carbonates

  • calcium carbonate (CaCO3) in lime, marble, and chalk

  • magnesium carbonate (MgCO3) in magnesite

  • calcium and magnesium carbonate (MgCO3.CaCO3) in dolomite

  • calamine (ZnCO3) as zinc carbonate


  • It is present in large amount in petrol, kerosene oil, diesel oil, grease, and wax.

  • Natural gas, marsh gas, petroleum gas, and coal gas contain carbon in the form of its compounds.

Allotropy: The phenomenon due to which an element exhibits different physical forms is called allotropy.

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