1.3.2 The Covalent Bond

The covalent bond consists of an electron pair that is shared between bonded atoms instead of giving up or gaining electrons. Two hydrogen atoms can form a covalent bond by sharing electrons. As a result of covalent bonding, each hydrogen acquires a stable, filled outer shell electronic configuration. Similarly, hydrogen and chlorine can form a covalent bond by sharing electrons.

Molecular structures that use this notation for the electron pair bond are called Lewis structures . A hydrogen atom can achieve a completely empty shell by losing an electron and become a positively charged hydrogen ion, called proton. A hydrogen atom can achieve a filled outer shell by gaining an electron, thereby forming a negatively charged hydrogen ion, called hydride ion.

In some covalent compounds, however, some valence electrons remain unshared. For example, water (H₂O) has six valence electrons. Two of these combine with hydrogens to make two O-H covalent bonds and four of the valence electrons remain unshared.

Ionic species such as [SO₂]^2- , [NH₄]⁺ and [BF₄]^- also contain covalent bonds. For an example, the tetrafluroborate anion contains covalent B-F bonds.

The charge on each atom is called formal charge and the sum of the formal charges on the individual atoms must be equal to the total charge on the ion.