Covalent Bond

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Covalent Bond:

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Covalent bond is a bond formed when two atoms share one or more electron pairs. Each atom contributes an equal number of electrons towards the bond formation.

electron-sharing

Types of Covalent Bonds:

The covalent bond is formed by mutual sharing of electrons between two atoms. The electrons that pair up to form a chemical bond are called ‘bond pair’ electrons. Depending upon the number of bond pairs, covalent bond is classified into following three types:

Single Covalent bond:

 When one electron is contributed by each bonded atom, one bond pair is formed and it forms a single covalent bond. A few examples of molecules with single covalent bonds are hydrogen (H2), chlorine (CI2), hydrochloric acid(HCl) & methane (CH4).
single-covalent-bond

Double Covalent Bond:

When each bonded atom contributes two electrons, two bond pairs are shared and a double covalent bond is formed. These bond pairs are indicated as a double line between those atoms in the structure of such molecules. The molecules like oxygen (O2) gas and ethene (C2H4) show such types of double covalent bonds.
double-covelent-c2h2

Triple Covalent Bond:

 When each bonded atom contributes three electrons, three bond pairs are involved in bond formation. This type is called triple covalent bond. Three small lines are used to indicate these three pairs of electrons between those atoms in the molecules. The examples of molecules having triple covalent bonds are nitrogen (N2) and ethyne (C2H2 ).  
triple-covalent-bond

Polar Covalent Bond:

When covalent bond is formed between two dissimilar atoms. is known as a polar covalent bond, characterised by a partial positive charge on one atom and a partial negative charge on the other.

EXPLANATION:

For example, the electrons in the H–Cl bond of a hydrogen chloride molecule spend more time near the chlorine atom than near the hydrogen atom. Thus, in an HCl molecule, the chlorine atom carries a partial negative charge and the hydrogen atom has a partial positive charge. Figure below shows the distribution of electrons in the H–Cl bond. We sometimes designate the positive and negative atoms in a polar covalent bond using a lowercase Greek letter “delta,” δ, with a plus sign or minus sign to indicate whether the atom has a partial positive charge (δ+) or a partial negative charge (δ–). This symbolism is shown for the H–Cl molecule.

 or      H δ+ –––––– Cl δ-

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