The atomic structure and atomic bonding of gold make it so malleable that it can be flattened to less than 400 times the thickness of a human hair.
Gold is the most malleable element, according to Mike Bullivant, a chemist at The Open University in Milton Keynes, England. Gold is so malleable that it can be hammered into sheets thinner than a wavelength of visible light, based on research from the University of Leeds in the UK in 1977. So, why is gold so malleable?
Gold does not tarnish with oxide layers on its surface like copper and silver. (Photo: Patrick Aventurier)
First, it is important to distinguish between malleability and softness. Malleability is a measure of how well a material can be hammered into a new shape without breaking. While other metals may shatter into pieces when excessively hammered, 28 grams of gold can be hammered into sheets with each side measuring 5 meters. Gold leaf can be made as thin as 0.000127 mm, which is about 400 times thinner than a human hair, according to the Jefferson Laboratory in Newport News, Virginia.
In contrast, there are various definitions of hardness and softness depending on how a material’s strength is tested. Based on the Mohs scale, which measures scratch resistance, the softest metal is cesium, soft enough to be cut with a butter knife, according to the Guinness World Records. However, Mark Jones, a chemical advisor and researcher at the American Chemical Society, states that the softest metal may be mercury, which is liquid at room temperature and more easily deformed than gold.
The malleability of gold is likely a result of two factors: “its atomic structure and how its atoms bond together,” says Dror Fixler, an optoelectronic engineer and director of the Bar-Ilan Institute of Nano Technology and Advanced Materials in Israel. The atomic structure of gold allows it to have a face-centered cubic crystal structure. In this structure, each atom is surrounded by 12 neighboring atoms. The arrangement of atoms in the face-centered cubic lattice allows for easy deformation without affecting the overall structure.
Additionally, gold is a metal. This means its atoms are held together by metallic bonds, where the outer electrons of each atom are free to move throughout the structure. This mobile cloud of electrons allows atoms to slide past one another easily, making gold malleable, Fixler explains.
However, Jones remains skeptical about whether these factors alone fully explain gold’s malleability. “Copper and silver also share similar electron configurations. They have similar chemical bonds but are not as malleable as gold. That means there must be other determining factors.“
Gold is less likely to form chemical bonds with other elements, which means gold particles do not tarnish with oxide layers on their surfaces like copper and silver do. The oxide layers make copper and silver more prone to fracturing. In contrast, the lack of oxide layers may contribute to gold’s superior malleability compared to other metals.
