Tetrachloroethylene (C2Cl4) is a nonpolar chlorinated hydrocarbon molecule. Its classification depends on its atomic structure and chemical bonds.
Understanding Molecular Polarity
Molecular polarity describes how electric charge is distributed across a molecule. A polar molecule has an uneven charge distribution, creating distinct positive and negative ends. Conversely, a nonpolar molecule has an even charge distribution, meaning no net poles exist.
The foundation of molecular polarity lies in bond polarity, which results from differences in electronegativity between bonded atoms. Electronegativity is an atom’s ability to attract shared electrons. For instance, in a carbon-chlorine (C-Cl) bond, chlorine has a higher electronegativity than carbon. This pulls electrons closer to chlorine, making the C-Cl bond polar. Importantly, a molecule can contain polar bonds yet still be nonpolar overall, depending on its symmetrical arrangement.
The Structure of Tetrachloroethylene
Tetrachloroethylene (C2Cl4) consists of two carbon atoms connected by a double bond (C=C), with each carbon also bonded to two chlorine atoms. Each carbon atom exhibits a trigonal planar geometry, meaning the carbon and its three attached atoms lie in a flat plane with bond angles of approximately 120 degrees. The entire molecule adopts a planar and highly symmetrical structure.
Why Tetrachloroethylene is Nonpolar
The nonpolar nature of tetrachloroethylene stems from the interplay between its polar bonds and its symmetrical molecular geometry. While each carbon-chlorine (C-Cl) bond is polar due to electronegativity differences, the molecule’s overall structure ensures these polarities cancel out. The two C-Cl bonds on each carbon atom create a bond dipole moment. However, due to the symmetrical trigonal planar arrangement around each carbon and the planar structure of the entire molecule, bond dipoles on one side of the carbon-carbon double bond are precisely counteracted by identical bond dipoles on the other side, leading to a net dipole moment of zero for the entire C2Cl4 molecule. The effect is similar to two equally strong forces pulling in opposite directions, resulting in no net movement.
How Nonpolarity Influences Tetrachloroethylene’s Properties
The nonpolar characteristic of tetrachloroethylene directly dictates many of its physical and chemical properties, particularly its solubility. Nonpolar substances tend to dissolve well in other nonpolar solvents. Consequently, C2Cl4 is not soluble in polar solvents like water, where its solubility is very low, ranging from 0.15 to 0.206 grams per liter at 25°C. Because of its ability to dissolve nonpolar organic materials, tetrachloroethylene is widely used as a solvent. It has been a leading solvent in dry cleaning operations since the 1940s, effectively removing oils and greases from fabrics, and its nonpolar nature also makes it an effective degreaser for metal parts in automotive and other metalworking industries.