Why is gold a metal but still soft and malleable? - 1000 Why

Описание: Why is gold a metal but still soft and malleable?

According to Mike Bullivant, a chemist at the Open University in Milton Keynes, UK, gold is the most malleable element. A 1977 study by the University of Leeds in the UK noted that gold is so malleable that it can be beaten thin enough to gild objects.

First, it is important to distinguish between malleability and softness. Malleability is a measure of how much a material can be hammered into a new shape without breaking.
While other metals break when hammered beyond a certain point, 28 grams of gold can be beaten into a sheet approximately 5 meters on one side, and gold leaf can be very thin, according to estimates by Jefferson Lab in Newport News, Virginia, USA.
Conversely, there are many definitions of hardness and softness, depending on how material strength is tested. Based on the Mohs scale, which measures a material's resistance to scratching, the softest metal is cesium, soft enough to be cut with a butter knife, according to the Guinness World Records.
Arguably, the softest metal might be mercury, which is liquid at room temperature and more deformable than gold, according to Mark Jones, a consulting chemist and member of the American Chemical Society. He said, "In my assessment, it is softer than gold."
What makes gold malleable?
Dror Fixler, an electro-optical engineer and director of the Bar-Ilan Institute of Nanotechnology and Advanced Materials in Israel, said the malleability of gold might stem from two factors: its atomic structure and the way its atoms bond with each other.
Fixler stated that the atomic structure of gold results in it having what's known as a face-centered cubic crystal structure.
He said, "In this structure, each atom is surrounded by 12 neighboring atoms. The arrangement of atoms in a face-centered cubic lattice allows for easy deformation without breaking the overall structure."
"Additionally, gold is a metal. This means its atoms are bonded together by metallic bonds, in which the outermost electrons of each atom can move freely around the overall structure of the material.
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However, when asked whether these factors alone can explain gold's malleability, Dr. Fixler said, "Copper and silver have similar configurations. They bond in the same way. They are not as soft as gold."
Dr. Mark Jones also stated that metals are often not a single large crystal; instead, they are made up of small crystals called grains. The 1977 University of Leeds study suggested that the grain size in which gold forms might explain its ductility.
Gold is famously unreactive with other elements. This means gold does not tarnish with oxide layers on its surface like silver and copper, Jones said. These oxides make copper and silver more brittle. In contrast, the absence of these oxides might help gold be more malleable than other metals.
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