Covalent bonds, covalent compounds and characteristics of covalent compounds

When the combining atoms have 4, 5, 6, or 7 electrons in the outermost or valence shell, they cannot donate electrons. Instead, they mutually share electrons in order to complete their octet in the outermost orbit or shell. Such a type of valency is referred to as covalency and the bond created between such atoms is called a covalent bond. The compounds so formed are called covalent compounds or molecular compounds.

Covalent Compounds

Covalent compounds are compounds formed by sharing of electrons between two reacting atoms mostly non-metallic resulting in formation of neutral molecules. The atoms mutually share equal number of electrons to achieve the configuration of a noble gas.

Molecule of Hydrogen (H = 1)

An example of sharing of one pair of electrons (single bond).

Two atoms of hydrogen share one pair of electrons to form a molecule of hydrogen (Fig. 3.4).

hydrogen molecule formation

Molecule of Oxygen (O = 8)

An example of sharing of two pairs of electrons (Double bond).

Two atoms of oxygen share two pairs of electrons to form one molecule of oxygen (Fig. 3.5).

oxygen molecule formation

Note :


In the above diagram only the valence or outermost shell of oxygen atom is shown.


Molecule of Nitrogen (N = 7)

An example of sharing of three pairs of electrons (Triple bond)

Two atoms of nitrogen share three pairs of electrons to form one molecule of nitrogen (Fig. 3.6).

nitrogen molecule formation

Note :



In the above diagram only the valence or outermost shell of nitrogen atom is shown.


Molecule of Chlorine (Cl = 17)

An example of sharing of one pair of electrons (Single bond)

Two atoms of chlorine share one pair of electrons to form one molecule of chlorine (Fig. 3.7).

chlorine molecule formation

Note :



In the above diagram only the valence or outermost shell of chlorine atom is shown.


Remember :

  • When one pair of electrons is shared between the atoms, a single bond is established between the atoms, e.g., H-H and Cl-Cl.
  • When two pairs of electrons are shared, a double bond is established, e.g., O=O.
  • When three pairs of electrons are shared, a triple bond is established, e.g., NN.

Molecule of Water (H = 1, O = 8)

Two hydrogen atoms mutually share one electron each with an atom of oxygen to form a water molecule (Fig. 3.8).

water molecules formation

Note :

In the above diagram only the valence or outermost shell of oxygen atom is shown.


Molecule of Hydrogen Chloride (H = 1, Cl = 17)

An atom of hydrogen and an atom of chlorine mutually share one pair of electrons to form a molecule of hydrogen chloride (Fig. 3.9).

hydrogen chloride formation

Note :

In the above diagram only the valence or outermost shell of chlorine atom is shown.


Molecule of Ammonia (H = 1, N = 7)

Three hydrogen atoms mutually share one pair of electrons each with a nitrogen atom to form a molecule of ammonia (Fig. 3.10).

ammonia formation

Note :

In the above diagram only the valence or outermost shell of nitrogen atom is shown.


Molecule of Methane (H = 1, C = 6)

Four atoms of hydrogen mutually share one pair of electrons each with a carbon atom to form a molecule of methane (Fig. 3.11).

methane molecule formation

Note :

In the above diagram only the valence or outermost shell of carbon atom is shown.


Molecule of Carbon Tetrachloride (C = 6, Cl = 17)

Out of the four valence electrons in carbon, one is made available for each chlorine atom for sharing to form a molecule of carbon tetrachloride (Fig. 3.12).

carbontetra chloride

Note :

In the above diagram only the valence or outermost shell of carbon and chlorine atoms are shown.


Molecule of Carbon Dioxide (C = 6, O = 8)

The two atoms of oxygen mutually share two pairs of electrons each with an atom of carbon to form a molecule of carbon dioxide (Fig. 3.13).

carbon dioxide formation

Note :

In the above diagram only the valence or outermost shell of carbon and oxygen atoms are shown.

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