Scientists Explain Why Gold Does Not Tarnish Unlike Other Metals
The Statue of Liberty, unveiled in 1886, was originally the warm metallic color of copper, the metal from which it is made. Over nearly 30 years, the statue developed a thick green patina, a protective layer formed by oxidation processes influenced by environmental moisture. This patina prevents further corrosion of the copper beneath. Had the statue been coated in gold, this color change would not have occurred, as gold naturally resists oxidation.
Gold’s resistance to tarnishing is due to its chemical inertness, meaning it rarely forms compounds with other atoms. Recent research published in Physical Review Letters explains that gold atoms on the surface arrange themselves in a hexagonal pattern that prevents them from binding with oxygen atoms, unlike other metals. Without this arrangement, gold would oxidize within seconds.
When metals oxidize, they first split oxygen molecules into atoms, which then bond with the metal surface, forming oxides or patinas. Researchers at Tulane University used quantum mechanics-based computer simulations to study how quickly gold would oxidize if its surface atoms were arranged differently. They found that the hexagonal atomic pattern on gold’s surface is far less effective at splitting oxygen molecules compared to a square lattice, making oxidation times a million to a trillion times longer.
Even if gold’s surface atoms were arranged in a square pattern, oxidation would produce an unstable oxide layer that would remain very thin. These findings not only explain gold’s enduring shine but also have implications for designing gold-based chemical catalysts. By manipulating gold’s surface atomic structure, scientists could enhance its reactivity or preserve its inertness, depending on the desired application.
This research highlights the unique atomic geometry responsible for gold’s noble properties, likening the hexagonal pattern to natural structures such as honeycombs and turtle shells. The study was summarized by Yehonatan Barkaiheim from the Davidson Institute for Science Education, affiliated with the Weizmann Institute of Science.
