Determining whether carbon and hydrogen are polar or nonpolar depends on how these elements interact within a chemical bond and as part of larger molecules.
Understanding Chemical Polarity
Chemical polarity describes the distribution of electrical charge within a bond or molecule. This distribution is determined by electronegativity, an atom’s tendency to attract electrons in a chemical bond. Atoms with higher electronegativity exert a stronger pull on shared electrons.
When two atoms form a covalent bond, they share electrons. If the atoms have identical or very similar electronegativities, the electrons are shared equally, resulting in a nonpolar covalent bond. However, if there is a noticeable difference in electronegativity, the electrons are pulled closer to the more electronegative atom, creating partial negative and partial positive charges across the bond. This unequal sharing leads to a polar covalent bond. Larger differences indicate more polar bonds.
Polarity of the Carbon-Hydrogen Bond
Applying the concept of electronegativity to the carbon-hydrogen bond helps clarify its polarity. On the Pauling scale, carbon has a value of approximately 2.55, and hydrogen is around 2.20. The difference between these values is 0.35.
Chemical guidelines generally consider a bond to be nonpolar covalent if the electronegativity difference between the bonded atoms is less than 0.5. Since the difference for the carbon-hydrogen bond falls within this range, the C-H bond is considered essentially nonpolar covalent. The electrons are shared nearly equally between the carbon and hydrogen atoms.
Polarity of Hydrocarbon Molecules
Hydrocarbons are compounds composed exclusively of carbon and hydrogen atoms. While each carbon-hydrogen bond possesses a minuscule degree of polarity, the overall polarity of hydrocarbon molecules is overwhelmingly nonpolar. This nonpolar characteristic arises from the symmetrical arrangement of C-H bonds throughout the molecule.
In typical hydrocarbon structures, such as methane or ethane, the slight individual bond dipoles from C-H bonds effectively cancel each other out due to the molecule’s symmetrical geometry. This means there is no net uneven distribution of electron density across the entire molecule. As a result, hydrocarbons lack distinct positive and negative poles.
The nonpolar nature of hydrocarbons explains why substances like oil do not mix with water. Water is a polar molecule, and the principle of “like dissolves like” dictates that nonpolar substances do not readily dissolve in polar solvents.