The freezing, melting, and sublimation of molecules are primarily governed by intermolecular forces and the energy balance between the molecules.
The phase transitions of substances (solid to liquid, liquid to gas, and vice versa) are influenced by several factors, including temperature and pressure. The behavior of molecules during these phase transitions is not directly related to their electron valence shells but rather to the interactions between the molecules themselves.
When a substance is heated, its internal energy increases, causing the molecules to move more rapidly. At a certain temperature, known as the melting point, the intermolecular forces holding the solid together become weak enough to allow the substance to transition from a solid to a liquid state (melting). This occurs when the average thermal energy of the molecules overcomes the attractive forces between them.
If the temperature continues to rise, the kinetic energy of the molecules further increases, causing them to move even more vigorously. At the substance's boiling point, the intermolecular forces are overcome completely, and the substance undergoes a phase transition from liquid to gas (vaporization or boiling). In this state, the molecules are no longer bound together and can move freely.
Sublimation, on the other hand, is the direct transition of a substance from the solid phase to the gas phase without passing through the liquid phase. This occurs when the vapor pressure of the solid exceeds the atmospheric pressure at a particular temperature, causing the solid to change directly into a gas. Sublimation can happen when the intermolecular forces holding the solid together are relatively weak, such as in the case of certain molecular solids.
The intermolecular forces that play a crucial role in these phase transitions include London dispersion forces, dipole-dipole interactions, and hydrogen bonding. These forces are determined by factors such as the molecular shape, polarity, and electron distribution of the molecules. However, it is important to note that while the electron configuration and distribution contribute to the overall properties of molecules, they do not directly determine the phase transitions or temperature/pressure gradients associated with them.