Why don’t we have corrosion in Gold?

Khrysos (Gold) is a child of Zeus; neither moth nor rust devoureth it; but the mind of man is devoured by this supreme possession.5th century Greek fragment.

A unique combination of chemical and physical properties make gold an invaluable assert in a wide variety of applications. Called as the ‘noble metal’, it is the least reactive metal at the gas and liquid interface causing its surface to never rust or tarnish. It is the only yellow metal, bearing its name from the old English word for yellow, ‘Geolu’.  Gold is present in the periodic table with the same group of copper and silver, both of which react with atmosphere causing copper oxide and silver oxide respectively. Even though gold falls in the same category, what is the difference in its structure that doesn’t allow it to be tarnished?

One of the primary reasons for this is the stability of its structure. With the atomic number 79, gold is one of the most inert materials chemically so it won’t react with other molecules. This means that reactive molecules will simply fall off the surface and never disturb the gold’s surface. It does, however react with the vicious solution of aqua regia (which is a mixture of concentrated hydrochloric acid and Nitric acid), but other than that there are no natural reactions to it allowing it to last almost forever. It doesn’t tarnish in the atmosphere, water or even sea water as evident by the centuries old sunken treasures recovered by deep sea explorers. Gold is one of the first materials to be identified as a ‘metal’ due to its occurrence in nature as ‘nuggets’.

However, with the advancement of technology, the barrier of gold being inert is now being broken by nanoscience. Previously assumed inert in its bulk form, gold is definitely ‘not inert’ in its nanoform. When used for nanotechnological applications (~10^-9m), the change in its surface to volume ratio allows it to react and contribute to typical catalysis reactions and other chemical reactions. These have applications in the domain of electronics, photodynamic therapy, therapeutic agent deliveries and in the new breed of nanotech based sensors.

It can be concluded by restating the question in two possible ways. The first is “Whether gold is reactive in its bulk form?” and “Whether gold remains inert in its nanoform?”

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