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Covalent Bond

A ​covalent bond is formed as a result of the sharing of a pair of electrons between atoms. Covalent bonds result when the difference in electronegativities between the bonding atoms is very small. Though the intramolecular bonds of covalent compounds are significant, the intermolecular forces are relatively weak. Because of this, covalent compounds have relatively lower boiling and melting points when compared to ionic compounds.

Covalent Bond Formation

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In this section, we will look at the covalent bond formation in the hydrogen molecule (H2). The hydrogen molecule is diatomic. The hydrogen atom has an electronic configuration of 1s1. The formation can be expressed in terms of Lewis formula as follows:


After the bond is formed, the electrons are shared by both hydrogen atoms, as expected in a covalent bond. This 1s overlap makes the configuration of hydrogen atom the same as that of helium (1s2). Another aspect that you should understand is that the total potential energy (see Figure 5-1) of the hydrogen molecule is lower than that of the hydrogen atoms in their separate forms. The potential energy diagram of hydrogen molecule formation should make this clear.

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The distribution of bonded electrons in the HBr molecule is shown above (Figure 5-2). In this bond formation, hydrogen shares its electron with bromine, whereas bromine gives the one electron that is needed for hydrogen to complete its shell. Bromine atom has 7 electrons in its outermost shell, and it requires 1 more to complete its octet. Octet is the state in which an atom has 8 electrons in its outermost shell. Now, since hydrogen has 2 electrons, and bromine has eight electrons in its valence shell, they are both satisfied in terms of their stability, the stability being facilitated by the formation of the covalent bond.

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