Carbon monoxide (CO) and carbon dioxide (CO2) are both molecules composed of carbon and oxygen atoms. However, they have different molecular structures and therefore have different polarities.
Let’s start by discussing carbon monoxide (CO). In this molecule, the carbon atom is bonded to the oxygen atom through a triple bond. The triple bond consists of one sigma bond and two pi bonds. The sigma bond is formed by the overlapping of atomic orbitals between the carbon and oxygen atoms, while the pi bonds result from the overlap of unhybridized p orbitals.
Due to the difference in electronegativity between carbon and oxygen, the oxygen atom attracts the shared electrons more strongly than the carbon atom. As a result, the oxygen atom has a partial negative charge (δ-) and the carbon atom has a partial positive charge (δ+). This unequal sharing of electrons creates a bond dipole, which is a measure of the polarity of a bond.
However, when we consider the molecule as a whole, the bond dipoles in carbon monoxide do not cancel each other out. This is because the molecule is linear, meaning that the carbon and oxygen atoms are in a straight line with each other. The bond dipoles are equal in magnitude but opposite in direction, resulting in a net molecular dipole moment of zero. Therefore, carbon monoxide is a nonpolar molecule.
Now let’s move on to carbon dioxide (CO2). In this molecule, there are two carbon-oxygen double bonds, and the carbon atom is bonded to two oxygen atoms. The geometry of carbon dioxide is linear, similar to carbon monoxide.
Similarly to carbon monoxide, the oxygen atoms in carbon dioxide attract the shared electrons more strongly than the carbon atom, resulting in partial negative charges on the oxygen atoms and a partial positive charge on the carbon atom. The bond dipoles in the carbon-oxygen bonds are equal in magnitude but opposite in direction, canceling each other out. However, when we consider the molecule as a whole, the bond dipoles do not cancel out, as the molecule is not symmetrical. The two bond dipole moments do not cancel each other out, resulting in a net molecular dipole moment.
The unequal distribution of charge in carbon dioxide makes it a polar molecule. The oxygen atoms are more electronegative than carbon, so they pull the electron density towards themselves, creating a partial negative charge on each oxygen atom and a partial positive charge on the carbon atom. This polarity gives carbon dioxide several unique properties, such as its ability to dissolve in water and its role in the greenhouse effect.
Carbon monoxide (CO) is a nonpolar molecule due to its linear structure, which allows the bond dipoles to cancel each other out. On the other hand, carbon dioxide (CO2) is a polar molecule due to its linear structure, which prevents the bond dipoles from canceling out and results in a net molecular dipole moment.