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Covalent Bond

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What is a Covalent Bond

A covalent bond, also known as a molecular bond, is a bond formed between two atoms by mutual sharing of electrons. Typically, the sharing of electrons allows each atom to fill their outermost shell completely, and thus, helps them achieve their stable electronic configuration.

Question : Explain the formation of dichlorine (Cl2) molecule.

Answer : The atomic number of chlorine is 17 and it has 7 valence electrons (3s23p5). Chlorine needs one electron to attain stable electronic configuration of argon, which has 8 valence electrons — 3s23p6.

In Cl2 molecule, each chlrine atom contributes one electron to form a common shared paired. By doing so, both of them complete their octets. In other words, they acquire the electronic configuration of argon.

formation of chlorine molecule : individual Cl atoms
formation of dichlorine molecule : sharing of electrons
formation of Cl2 molecule

The shared pair of electrons can be represented by dash as given below:

formation of Cl2
More Practice Questions

Covalency

The number of electrons an atom shares with other atoms to form a chemical bond is called its covalency. For example, in Cl2 molecule, each chlorine atom shares one electron; therefore, the covalency of chlorine is 1. Similarly, in CH4 (methane), the covalency of carbon is 4, and that of hydrogen is 1.

Covalent Bond Between Different Types of Atoms

The formation of covalent bond does not necessarily require atoms of same element. Two atoms of different elements can also share electrons to form a covalent bond provided they are of comparable electronegativity. Example: In HCl molecule, hydrogen and chlorine contribute one electron each to form a shared pair of electrons.

Hydrogen and chlorine

formation of HCl

HCl molecule

formation of hydrogen chloride

Effect of Electronegativity on Covalent Bonds

When two atoms of same elements form a covalent bond, the electron pairs are shared equally between the two atoms. But, when a covalent bond is formed between atoms of different electronegativities, the shared pair of electrons gets displaced towards the atom which is more electronegative. As a result, one end of the molecule becomes slightly positively charged, and the other end becomes slightly negatively charged. For more, please read our polarity of bonds tutorial.

Types of Covalent Bonds

There are different types of covalent bonds:

Single, Double, and Triple Covalent Bonds

Single bond in H2

Single bond example : H2

or

H2 contains a single bond

Double bond in O2

Double bond example : O2

or

O2 contains a double bond

Triple bond in N2

Triple bond example : N2

or

N2 contains a triple bond

Polar and Non-polar Covalent Bonds

Polar molecules

Polar molecules example : HCl
HF is a polar molecule
H2O is polar

Non-polar molecules

H2 is non polar
non polar molecules example : Cl2
F2 is polar

For more useful information, refer to polarity of bonds.

Sigma and Pi Bonds

When two atoms combine together to form a covalent bond, they are so close to each other that their orbitals are partially merged. This is called overlapping of orbitals.

There are two types of covalent bonds based on nature of overlap:

  1. Sigma (σ) bond
  2. Pi (π) bond

A single bond is usually a σ bond. A double bond consists of one σ bond and one π bond, and a triple bond consists of one σ and two π bonds. We will study about σ and π bonds in overlapping of orbitals.

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