Benzene (C6H6) and naphthalene (C10H8) are both aromatic hydrocarbons, but they exhibit significantly different physical properties such as boiling points and melting points. The boiling point of benzene is approximately 80°C, while naphthalene has a boiling point of 218°C. Similarly, benzene has a melting point of 6°C compared to naphthalene’s higher melting point.
The key to understanding these differences lies in the intermolecular forces present in each compound. Benzene is a smaller molecule with a lower molecular weight, which primarily exhibits London dispersion forces (a type of van der Waals force) due to its nonpolar nature. These forces are relatively weak and are a result of temporary dipoles that arise when electron clouds of molecules fluctuate.
Naphthalene, on the other hand, is a larger and more complex molecule with a greater number of electrons. This larger electron cloud enhances the strength of the London dispersion forces due to increased polarizability. Additionally, naphthalene can interact more effectively through π-π stacking interactions because it has a more extensive conjugated system, which contributes to stronger intermolecular attractions than those found in benzene.
As a result, the stronger intermolecular forces in naphthalene require more energy (in the form of heat) to overcome these interactions when transitioning to the gas phase, thus explaining its higher boiling point. Similarly, naphthalene’s greater intermolecular forces necessitate more energy for melting compared to benzene, leading to its higher melting point.
In summary, the differences in the physical properties of benzene and naphthalene can be attributed to their molecular sizes and the resulting differences in intermolecular forces, with naphthalene exhibiting stronger dispersion forces and additional π-π interactions.