Not All That’s Gold Does Glitter

Generally, when one looks up the properties of an element such as gold in an encyclopedia, one is immediately confronted with a list of established facts and figures. While many people are aware that most countries do not rely on a “gold reserve” anymore, it is surprising to learn that even basic physical and chemical properties of something as familiar as gold are not as fixed as one may believe. The reason for this is that tabulated values for material properties inevitably refer to macroscopic samples. It turns out that many simple properties such as those listed in the definition given here go spectacularly wrong as the size of the piece of gold is reduced. One of the most dramatic demonstrations of this was provided by Buffat and Borel, who measured the melting point of gold particles as a function of particle size using an electron microscope. They found that by the time gold crystals are just 4 nm across, the melting point drops to 700 K from its “encyclopedia value” of 1337 K. Another example is the noble character of gold metal.