Polar covalent compounds generally exhibit higher melting and boiling points compared to non-polar covalent compounds of similar molecular mass. This difference primarily arises from the type of intermolecular forces present in these substances.
In polar covalent compounds, there exists a significant difference in electronegativity between the bonded atoms, leading to a partial positive charge on one end of the molecule and a partial negative charge on the other. This asymmetry allows for dipole-dipole interactions between the positively charged part of one molecule and the negatively charged part of another. These interactions are relatively strong and require more energy to break, resulting in higher melting and boiling points.
On the other hand, non-polar covalent compounds are characterized by an even distribution of electrical charge. The intermolecular forces present in these substances are primarily London dispersion forces, which are much weaker than dipole-dipole interactions. Consequently, less energy is needed to break these forces, leading to lower melting and boiling points compared to their polar counterparts.
In summary, the stronger intermolecular forces in polar covalent compounds due to their dipole-dipole interactions contribute to their higher melting and boiling points when compared to non-polar covalent compounds of similar molecular mass.