Carbon dioxide (CO2) is a nonpolar molecule. Molecular polarity describes the distribution of electrical charges within a molecule, indicating if one end carries a slight positive charge and the other a slight negative charge.
What Makes a Molecule Polar?
The polarity of any molecule depends on two primary factors: the difference in electronegativity between its bonded atoms and the molecule’s three-dimensional shape. Electronegativity is a measure of an atom’s ability to attract electrons within a chemical bond. When two atoms with different electronegativities form a bond, the electrons are unequally shared, creating a “polar bond.” The atom with greater electronegativity pulls the shared electrons closer, gaining a slight negative charge, while the other atom develops a slight positive charge.
Examples of polar bonds include the oxygen-hydrogen (O-H) bond in water or the carbon-oxygen (C-O) bond, where oxygen is more electronegative than hydrogen or carbon. In contrast, bonds between atoms with very similar or identical electronegativities, such as carbon-carbon (C-C) or hydrogen-hydrogen (H-H), result in equal sharing of electrons and are considered nonpolar bonds.
Molecular geometry also determines overall polarity. If the molecule’s shape is symmetrical, individual polar bonds can cancel each other out, leading to a nonpolar molecule. Conversely, an asymmetrical arrangement of polar bonds results in an overall polar molecule. For instance, a bent shape, like that of a water molecule, causes an unequal distribution of charge, making it polar, whereas a linear or tetrahedral shape can lead to charge cancellation.
Why Carbon Dioxide is Nonpolar
Carbon dioxide (CO2) consists of one carbon atom double-bonded to two oxygen atoms. Each carbon-oxygen (C=O) bond within the CO2 molecule is polar. This polarity arises because oxygen has a higher electronegativity than carbon, meaning oxygen attracts the shared electrons more strongly. This unequal sharing gives each oxygen atom a slight negative charge and the central carbon atom a slight positive charge.
The CO2 molecule is nonpolar due to its specific molecular geometry. Carbon dioxide has a linear shape, with the carbon atom in the middle and the two oxygen atoms directly opposite each other, forming a 180-degree angle. This linear and symmetrical arrangement means the pull of electrons towards one oxygen atom is counteracted by the equal and opposite pull towards the other.
These opposing forces, known as bond dipoles, cancel each other out, resulting in a net molecular dipole moment of zero. Because of its nonpolar nature, CO2 has limited solubility in polar solvents like water, following the general principle that “like dissolves like.”