The oxygen molecule, chemically written as \(\text{O}_2\), is abundant in Earth’s atmosphere and necessary for respiration. When two oxygen atoms bond, the resulting chemical connection is classified as a covalent bond. This classification depends on how the atoms interact with their outermost electrons, determining whether the bond involves a transfer or a sharing of these valence electrons.
Defining Covalent and Ionic Bonds
Chemical bonds form as atoms attempt to achieve a more stable electron configuration by filling their outermost electron shell. The difference between ionic and covalent bonds lies in the movement of valence electrons. Ionic bonds involve the complete transfer of one or more electrons, resulting in the formation of charged particles called ions. This typically occurs between a metal (losing electrons) and a non-metal (gaining electrons), creating an electrostatic attraction between the oppositely charged ions.
Covalent bonds, in contrast, form when atoms share one or more pairs of valence electrons between them. This sharing allows both atoms to effectively complete their outer electron shells without transferring charge. Covalent bonding typically occurs between two non-metal atoms, such as the two oxygen atoms in the \(\text{O}_2\) molecule. The shared electrons orbit both nuclei, holding the atoms together in a stable molecular structure.
How Electronegativity Classifies Bonds
Chemists use the concept of electronegativity to categorize the nature of a chemical bond. Electronegativity is an atom’s ability to attract a shared pair of electrons toward itself within a bond. The bond type is determined by calculating the absolute difference in their respective electronegativity values (\(\Delta\text{EN}\)).
A large difference in electronegativity (greater than 1.7 on the Pauling scale) means one atom pulls the electron completely away, resulting in an ionic bond. If the difference is moderate (between 0.4 and 1.7), the electrons are shared unequally, creating a polar covalent bond. A zero or very small difference (less than 0.4) indicates that the electrons are shared equally, forming a nonpolar covalent bond.
Analyzing the Bond in the \(\text{O}_2\) Molecule
The oxygen molecule is composed of two identical oxygen atoms bonded together. The electronegativity value for a single oxygen atom is approximately 3.44 on the Pauling scale. To determine the bond type, one must calculate the difference in electronegativity between the two bonded atoms.
Since both atoms are oxygen, the calculation involves subtracting the atom’s electronegativity value from itself, resulting in an electronegativity difference of zero. This zero difference means neither oxygen atom can pull the shared electrons away from the other, forcing a perfectly equal sharing between the two nuclei. The equal sharing of electrons is the defining characteristic of a nonpolar covalent bond.
The bond in \(\text{O}_2\) is therefore classified as a nonpolar covalent bond, representing the purest form of covalent bonding possible. The equal sharing confirms that no ions are formed, eliminating the possibility of the bond being ionic. This nonpolar covalent structure results in oxygen gas being a stable, neutral molecule.