Methane has a low boiling point of -161.5°C (-258.7°F) primarily due to its molecular structure and the type of intermolecular forces present. Methane (CH4) is a small, non-polar molecule composed of one carbon atom and four hydrogen atoms. Its low molecular weight contributes to its low boiling point compared to larger molecules.
The key factor that explains methane’s boiling point is the strength of the intermolecular forces acting between its molecules. In the case of methane, the only significant intermolecular force is London dispersion forces (also known as van der Waals forces). These forces are relatively weak and arise due to temporary dipoles that occur when the electron distribution within a molecule changes.
In contrast, larger molecules or polar molecules experience stronger intermolecular forces, such as hydrogen bonding or dipole-dipole interactions, which require more energy to overcome when transitioning from a liquid to a gas. Since methane does not have these stronger intermolecular forces, it transitions to gas at a much lower temperature.
Thus, the combination of methane’s small size, low molecular weight, and the weak nature of the intermolecular forces accounts for its low boiling point.