The idea of a metal that can be chewed like gum suggests a material with extreme pliability. While most metals are rigid and hard, a few elements possess unusual softness and low melting points that bring this concept close to reality. These post-transition metals sit near the boundary between metals and nonmetals on the periodic table, giving them unique characteristics. Their ability to dramatically change shape under slight pressure, or even liquefy at body temperature, makes them fascinating subjects in material science.
Identifying the Ultra-Malleable Metals
The two primary candidates for this unusual designation are Indium and Gallium. Indium is a silvery metal known for its exceptional softness; it can be scratched with a fingernail or easily cut with a knife. It is classified as one of the softest metals on the Mohs hardness scale, allowing it to be pressed and molded without fracturing. This extreme malleability makes Indium the element most often associated with the notion of a “chewable” metal.
Gallium is also a soft, silvery metal, but it is famous for its extremely low melting point of approximately 29.8 degrees Celsius (85.6 degrees Fahrenheit). This temperature is slightly below typical human body temperature, meaning pure Gallium will liquefy if held in the palm of your hand. While less malleable than Indium in its solid state, its tendency to melt almost instantly in the mouth creates a different kind of unusual behavior.
The Science Behind Their Softness
The physical properties of these elements relate directly to their atomic arrangement and bonding. Indium’s softness stems from its unique crystal structure, a body-centered tetragonal lattice. This structure arranges atoms in layers that easily slide past one another when compressive force is applied. This non-directional bonding allows the metal to be deformed dramatically without breaking, a phenomenon that even produces an audible “cry” when the metal is bent.
Gallium’s low melting point is due to its unusual orthorhombic crystal structure. Unlike most metals, solid Gallium forms pairs of atoms, known as Ga₂ dimers. The bonds within these pairs are strong, but the bonds between the pairs are weak. This requires very little thermal energy to break the lattice apart and transition into a liquid state, making the solid form unstable at slightly elevated temperatures.
Safety and Toxicity of Ingesting Soft Metals
Although the elemental forms of Indium and Gallium are considered to have low acute toxicity, ingesting any metal carries significant health risks. Indium’s long-term effects and the toxicity of its soluble salts are not fully characterized, and chronic exposure has been linked to severe lung disease in occupational settings. Furthermore, the physical act of chewing and swallowing a foreign object risks internal damage.
Ingesting a piece of metal that does not dissolve can lead to intestinal blockage or trauma. Gallium presents a specific and serious risk to dental health because it is corrosive to other metals, particularly aluminum. Since many modern dental fillings, crowns, and braces contain aluminum alloys, Gallium metal could aggressively attack and destroy this dental work upon contact.
Practical Uses in Technology and Health
The unique properties of these metals are utilized extensively in modern technology and medicine. Indium’s greatest application is in the form of Indium Tin Oxide (ITO), a compound that is both transparent and electrically conductive. This material is deposited as a thin film on glass to create the touchscreens and liquid crystal displays (LCDs) found in smartphones, tablets, and televisions. Indium is also used in solders that join electronic components, valued for creating strong bonds at low temperatures.
Gallium is a foundational element in high-speed electronics and optoelectronics due to its semiconductor properties. Compounds like Gallium Arsenide (GaAs) and Gallium Nitride (GaN) are used to manufacture Light Emitting Diodes (LEDs), laser diodes, and high-frequency radio chips for applications like 5G communication. In medicine, Gallium compounds are used in diagnostic imaging and nuclear medicine because they can mimic iron in the body, helping to detect inflammation or tumors. Gallium and Indium are also alloyed with tin to create Galinstan, a non-toxic liquid metal replacement for mercury in thermometers.