Ethanol, the common alcohol with the chemical formula C2H5OH, is a widely encountered organic compound used in everything from beverages to fuels and solvents. Ethanol is definitively a covalently bonded molecule.
Defining the Two Primary Chemical Bonds
Chemical compounds are held together by forces of attraction that fall primarily into two categories: ionic and covalent bonds. These bond types are distinguished by how the atoms manage their valence, or outermost, electrons. Ionic bonds typically form between a metal and a nonmetal, such as in table salt, sodium chloride (NaCl).
In an ionic bond, one atom completely transfers one or more electrons to another atom, resulting in the formation of charged particles called ions. The atom that loses electrons becomes a positively charged cation, while the atom that gains electrons becomes a negatively charged anion. These oppositely charged ions are then held together by a strong electrostatic force of attraction.
Covalent bonds, in contrast, primarily occur between two nonmetals. Instead of transferring electrons, the atoms share one or more pairs of electrons to achieve a stable electron configuration. This sharing creates a strong link between the atoms, forming a distinct molecular unit, such as in water (H2O). The type of atoms involved—metals and nonmetals—is the simplest way to predict which bond type will form.
The Molecular Architecture of Ethanol
The reason ethanol is covalent becomes clear upon examining its atomic makeup, which includes Carbon (C), Hydrogen (H), and Oxygen (O). All three of these elements are classified as nonmetals on the periodic table. Since the atoms in ethanol are exclusively nonmetals, they must bond by sharing electrons rather than by transferring them.
The molecular structure of ethanol involves a chain of two carbon atoms. The atoms are linked together by a series of single covalent bonds, including a carbon-carbon bond (C-C), several carbon-hydrogen bonds (C-H), and a carbon-oxygen bond (C-O). The hydroxyl functional group (-OH) is covalently bonded to one of the carbon atoms. This hydroxyl group is what makes the compound an alcohol.
How Covalent Bonds Shape Ethanol’s Physical Behavior
The covalent nature of ethanol is directly responsible for many of its most recognizable physical properties, which differ significantly from ionic compounds. Unlike ionic compounds that form rigid, high-melting-point crystal lattices, covalent compounds exist as discrete molecules. These individual molecules are held together by weaker intermolecular forces, which are much easier to overcome than the strong electrostatic forces found in ionic lattices.
This is why ethanol is a colorless liquid at room temperature, with a relatively low boiling point of 78.37 °C (173.07 °F). If ethanol were ionic, its boiling point would be hundreds of degrees higher, and it would likely be a solid under typical conditions. The hydroxyl group (-OH) within the covalent structure introduces a slight charge separation, creating a polar region in the molecule. This internal polarity explains why ethanol mixes easily with water, making it an effective solvent.