Covalent compounds are formed by the mutual sharing of electrons by the combining atoms. Formation of some typical covalent compound is described below:
1. Formation of a chlorine molecule:
The electronic configuration of chlorine 2, 8, 7. a chlorine atom has seven valence electrons. Thus chlorine atom requires only one electron to acquire a stable configuration of argon. Two chlorine atoms achieve stable configurations by mutual sharing of one pair of electrons, viz.,
2. Formation of ammonia molecule:
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The electronic configuration of nitrogen and hydrogen are , Nitrogen 2, 5 and Hydrogen 1. Thus, each nitrogen atom needs 3 electrons to complete its octet, while each hydrogen atom would need only one electron to acquire the stable configuration of helium (the nearest noble gas). To do so, three hydrogen atoms tend to share one electron pair each with the nitrogen atom.
There are three single covalent bonds in a molecule of ammonia. The unshared pair of electrons on the nitrogen atom of ××NH3 does not take part in bond formation. Therefore, it is called a lone-pair of electrons.
3. Formation of methane:
Methane molecule contains one atom of carbon and four atoms of hydrogen, i.e.; the molecular formula of methane are CH4. The electronic configuration of carbon is 2, 4 and that of hydrogen is 1. Carbon atom in CH4 thus shares 4 pairs of electrons, one pair with each hydrogen atom, in methane, carbon atom is linked to four hydrogen atoms by C-H single bonds.
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4. Formation of carbon tetrachloride:
Molecular formula of carbon tetrachloride is CCl4. The electronic configuration of carbon is (2, 4) and that of chlorine (2, 8, 7). The carbon atom is four electrons short of its octet, and each chlorine atom requires one electron to complete its octet. Thus , each chlorine atom shares one electron pair with carbon atom,
5. Formation of carbon dioxide molecule:
In carbon dioxide (CO2) molecule, carbon is linked to two oxygen atoms by carbon-oxygen double bonds. This is shown below
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6. Formation of hydrogen cyanide molecule:
Hydrogen cyanide is a molecule in which one carbon atom is bonded to one hydrogen atom and one nitrogen atom. Carbon atom shares one electron apir with hydrogen atom, and three electron pair with hydrogen atom, and three electron pair with nitrogen atom. Thus, in hydrogen cyanide molecule there is one C-H single bond, and one C≡ N triple bond. This is shown below.