The molecule \(\text{CH}_3\text{CH}_3\), known as Ethane, is one of the simplest hydrocarbons, consisting only of carbon and hydrogen atoms. Determining whether this molecule is polar or nonpolar requires examining its chemical bonds and its three-dimensional structure. This analysis is fundamental to understanding Ethane’s physical properties, such as how it interacts with other substances.
What Makes a Molecule Polar or Nonpolar
Molecular polarity is a property arising from the distribution of electrical charge across a molecule. This distribution is determined by two main factors: bond polarity and the molecule’s overall shape. Bond polarity itself results from a difference in the electronegativity values of the two atoms forming the bond. Electronegativity is the measure of an atom’s ability to attract a shared pair of electrons toward itself in a chemical bond.
When two atoms in a bond have different electronegativities, the electron density shifts toward the more attractive atom, creating a partial negative charge (\(\delta^-\)) near that atom and a partial positive charge (\(\delta^+\)) near the other atom. This charge separation creates an individual bond dipole moment. If the electronegativity difference is very small (generally less than 0.5), the bond is considered nonpolar, meaning electrons are shared nearly equally.
For a molecule containing multiple bonds, like Ethane, the overall polarity is determined by the vector sum of all individual bond dipoles. If these individual dipoles are arranged symmetrically, they can pull on the central atom with equal force in opposing directions, effectively canceling each other out. A molecule with bond dipoles that cancel results in a net dipole moment of zero and is therefore classified as nonpolar. Conversely, if the bond dipoles do not cancel due to an asymmetrical shape, the molecule will possess a net dipole moment and be considered polar.
The Chemical Structure of Ethane
Ethane has the chemical formula \(\text{C}_2\text{H}_6\). Its structure involves a single covalent bond between the two carbon atoms (\(\text{C-C}\)), with each carbon atom also bonded to three hydrogen atoms (\(\text{C-H}\)). The \(\text{C-C}\) bond is inherently nonpolar.
Each carbon atom in Ethane is \(sp^3\) hybridized, which dictates the molecule’s three-dimensional arrangement. This hybridization results in a tetrahedral geometry around each carbon center. The bond angles between the atoms are approximately 109.5 degrees, forming a structure that is highly symmetrical.
The six hydrogen atoms are spread out uniformly around the central \(\text{C-C}\) axis. This uniform distribution of surrounding atoms is a major determinant of the molecule’s overall electronic character, as the \(\text{C-H}\) bonds are the only ones that could potentially introduce polarity.
Why Ethane is Nonpolar
Ethane is classified as a nonpolar molecule based on its bond characteristics and molecular geometry. The first factor is the minimal difference in electronegativity between carbon (2.5) and hydrogen (2.1), resulting in a difference of only 0.4. This difference is so small that the \(\text{C-H}\) bond is often treated as nonpolar, or at best, only very slightly polar.
Even if the \(\text{C-H}\) bonds possess minute individual dipole moments, the overall molecular structure ensures they do not create a net charge separation. The tetrahedral geometry around each carbon atom means that the three \(\text{C-H}\) bond dipoles connected to that carbon are oriented symmetrically in space. These symmetrical vectors effectively pull against one another, causing them to cancel out completely.
The result is that the molecule has no overall net dipole moment. This nonpolar nature dictates Ethane’s behavior in mixtures, following the general chemistry rule known as “like dissolves like.” Since Ethane is nonpolar, it is virtually insoluble in polar solvents like water. Instead, Ethane readily mixes with other nonpolar substances, such as oils or organic solvents, which share a similar structure.