Carbon monoxide (CO) is a highly toxic, odorless, and colorless gas frequently produced as a byproduct of the incomplete burning of fuels. Chemical compounds are classified based on the type of bond holding their atoms together: ionic (electrons transferred) or covalent (electrons shared). Understanding this classification reveals the definitive structure of CO.
The Chemical Nature of Carbon Monoxide
Carbon monoxide is classified as a covalent compound because the bond between carbon and oxygen atoms involves the sharing of electrons. Both carbon and oxygen are non-metals, and compounds formed exclusively between non-metal atoms nearly always result in covalent bonds.
The covalent structure is also supported by the small difference in electronegativity between the two atoms. Electronegativity measures an atom’s ability to attract electrons in a bond. A large difference typically causes electron transfer, resulting in an ionic bond. Since the difference between carbon and oxygen is not substantial, they engage in sharing electrons to form a discrete molecule.
The Mechanism of Covalent Bonding
The covalent bond in carbon monoxide is formed by sharing three pairs of electrons between the carbon and oxygen atoms. This sharing allows both atoms to achieve a stable outer electron shell, following the octet rule. The resulting strong connection is known as a triple bond, which holds the molecule in a linear configuration.
The Triple Bond Structure
The formation of this triple bond involves a coordinate covalent bond. Initially, carbon and oxygen share two pairs of electrons, which leaves the carbon atom unstable. To complete carbon’s stable outer shell, the oxygen atom contributes both electrons for the third shared pair. Once established, this coordinate bond functions identically to the other shared pairs, resulting in a single, stable triple covalent bond for the CO molecule.
Distinguishing Carbon Monoxide from Ionic Compounds
Ionic compounds, in contrast to covalent ones like carbon monoxide, are characterized by the complete transfer of electrons from one atom to another. This transfer typically occurs between a metal atom and a non-metal atom, such as in table salt, which is sodium chloride (NaCl). The metal loses electrons to become a positively charged ion (cation), and the non-metal gains electrons to become a negatively charged ion (anion).
The resulting oppositely charged ions are held together by strong electrostatic attraction, forming an ionic bond. This process requires a large difference in electronegativity between the two atoms, often exceeding a value of 1.7. Since carbon monoxide is composed of two non-metal atoms and relies on electron sharing, it lacks the electron transfer and charged ion formation that define an ionic compound.