The element Gallium (Ga), atomic number 31, is classified as a metal, despite possessing physical characteristics unusual for its class. At standard temperature and pressure, pure gallium is a soft, silvery-white solid, but it quickly transitions to a liquid state under slightly warmer conditions. Gallium exhibits the fundamental chemical and physical traits expected of a metal, such as electrical conductivity, yet its behavior at room temperature is what sets it apart.
Gallium’s Position as a Metal
Gallium is situated in Group 13 of the periodic table, next to the metalloids, and is categorized as a post-transition metal. Like other metals, gallium atoms readily lose their three valence electrons to form positive ions with a +3 oxidation state in chemical compounds. This propensity for cation formation is a defining chemical characteristic of metals.
In its solid state, the element is an excellent conductor of both heat and electricity, similar to aluminum, which sits directly above it on the periodic table. Pure, solid gallium metal displays a brilliant, silvery luster and, if fractured, breaks in a conchoidal pattern, similar to glass. It forms alloys with most other metals and is sometimes used in solders and low-melt alloy mixtures.
The Anomaly of a Low Melting Point
The most distinctive physical property of gallium is its extraordinarily low melting point of approximately 29.76 degrees Celsius (85.57 degrees Fahrenheit). This temperature is only slightly above the average room temperature and is well below the normal human body temperature of 37 degrees Celsius. A piece of solid gallium will melt completely if held in a person’s hand, turning into a silvery, water-like liquid.
This low melting point is an anomaly when compared to common metals like iron, which melts at over 1,500 degrees Celsius, or copper, which melts at over 1,000 degrees Celsius. The element has one of the largest liquid ranges of any known substance, as its boiling point is exceptionally high, over 2,200 degrees Celsius. Because of this wide range, liquid gallium can be used as a non-toxic replacement for mercury in high-temperature thermometers.
Gallium also exhibits a strong tendency toward supercooling, meaning it can remain in a liquid state even when cooled far below its melting point unless a small seed crystal is introduced to initiate solidification. Another unusual trait is that, like water, gallium is one of the few materials that expands in volume by about 3.1% when it transitions from a liquid to a solid. This expansion means that solid gallium floats on its own liquid.
Essential Role in Modern Technology
Gallium’s unique properties, particularly its electronic structure, make it indispensable in the modern technology sector, predominantly in the form of semiconductor compounds. The most common application involves its combination with arsenic to form Gallium Arsenide (GaAs) or with nitrogen to form Gallium Nitride (GaN). These compounds are categorized as III-V semiconductors, named for the periodic table groups of their constituent elements.
Gallium Arsenide is widely used in radio frequency integrated circuits for applications like Wi-Fi and Bluetooth devices found in smartphones and tablets. GaAs allows for much higher operating speeds than traditional silicon-based chips, making it valuable for high-speed communication and microwave circuits. Gallium Nitride has become fundamental in the creation of high-brightness blue and white Light Emitting Diodes (LEDs), which are now prevalent in modern lighting and display screens.
The GaN compound is also increasingly utilized in power electronics, such as smaller, more efficient chargers for mobile devices and in specialized components for electric vehicles. Furthermore, gallium-based compounds are important in specialized solar power applications, particularly in multi-junction solar cells used on spacecraft, where their efficiency is superior to silicon.