Gallium (Ga), element 31, is a metal that is solid at standard room temperature but possesses an exceptionally low melting point. This silvery-white metal liquefies at approximately 29.76 °C (85.57 °F), well below human body temperature. Consequently, solid gallium will readily melt if held in a person’s hand, transitioning quickly into a liquid state.
The Element Gallium
Gallium is classified as a post-transition metal and resides in Group 13 of the periodic table, situated between aluminum and indium. It is a soft, silvery metal, though it often appears coated with a thin layer of its native oxide, which gives it a slightly blue-gray tint. Gallium is not found naturally as a free element but is present in trace amounts within minerals like bauxite and zinc ores. It is primarily recovered as a byproduct during the refinement of these other, more abundant metals.
Why Gallium Melts So Easily
The low melting point of gallium results from its unique crystalline structure in its solid form. Unlike most metals, which form highly symmetrical, closely packed crystal lattices, solid gallium has an orthorhombic structure. Within this complex structure, the atoms form weakly bonded pairs, known as dimers (\(\text{Ga}_2\)).
These \(\text{Ga}_2\) dimers exhibit a strong, almost covalent bond between the two atoms. However, the bonds connecting these dimers to the surrounding lattice are comparatively weak. Since these weak bonds require very little energy to break, gallium transitions to a liquid state at a much lower temperature than its neighboring elements on the periodic table, despite having a high boiling point.
Behavior of Liquid Gallium
Once liquid, gallium displays properties unusual for a metal. One notable trait is its tendency to “wet” or stick strongly to many surfaces, including glass and porcelain, due to the formation of an oxide layer upon contact with air. This characteristic means it leaves a reflective residue on most materials.
Liquid gallium also exhibits a density anomaly, similar to water, where its liquid phase is denser than its solid phase. Consequently, solid gallium will float when placed in liquid gallium. While the melting point is very low, its boiling point is over 2,200 °C, giving it one of the largest liquid temperature ranges of any element. Gallium also shows a strong ability to supercool, remaining liquid well below its melting point unless disturbed by a seed crystal or vibration.
How Gallium is Used
The properties of gallium make it valuable in high-technology applications, particularly in the electronics industry. Its primary use is in the creation of compound semiconductors like gallium arsenide (GaAs) and gallium nitride (GaN). These compounds are favored over silicon because they allow for faster switching speeds and higher operating temperatures.
Gallium-based semiconductors are used to manufacture blue and white Light Emitting Diodes (LEDs), lasers, and radio frequency integrated circuits found in modern cell phones and Wi-Fi devices. Because of its low melting point, gallium is also used in thermal management applications. Liquid gallium or its alloys are employed as a non-toxic replacement for mercury in high-temperature thermometers and as a thermal interface material to efficiently transfer heat away from high-power electronic components.