Final answer:
Gallium exhibits the unusual property of expanding upon solidifying due to the thermal expansion principles and its unique molecular structure in the solid phase. This behavior is linked to the increased kinetic energy of atoms at lower temperatures and the specific Ga2 molecular formation, generally making gallium's solid structure less dense than its liquid state.
Step-by-step explanation:
The question relates to the unique property of the element gallium (Ga), which forms Ga2 molecules within its crystal lattice. Gallium is known to expand upon solidifying, unlike most other substances that contract when they freeze.
The underlying cause of this expansion lies in the thermal expansion of matter and the specific arrangement of atoms within the solid structure of gallium.
The principle of thermal expansion dictates that as temperature increases, the kinetic energy of atoms and molecules also increases. In the case of a solid, which has tightly packed atoms or molecules, the increased kinetic energy causes the atoms to vibrate more vigorously, pushing against their neighbors.
This results in greater average distances between neighboring atoms, leading to an expansion in the material's size. For gallium, the Ga2 molecular formation in its solid phase may result in a less dense structure when the temperature decreases.
This less dense structure could allow the solid to expand upon freezing. The anomaly of gallium's expansion while solidifying can be aligned with the standard concept of thermal expansion, where kinetic energy and molecular interactions play key roles.
Furthermore, compression is more favorable to a denser phase. Since gallium is originally a solid around 301.9K, a further drop in temperature can prompt a phase change towards a liquid state.
In this reverse scenario, the compression of the liquid phase would not be as favorable, leading to the expansion of gallium as it transitions to a solid.