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).

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).

Note :

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

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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).

Note :

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

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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).

Note :

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

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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.

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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).

Note :

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

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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).

Note :

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

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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).

Note :

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

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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).

Note :

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

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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).

Note :

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

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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).

Note :

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