Gold (Au, atomic number 79) has been prized for millennia, not just for its striking color but for its enduring nature. It has been a foundation for currency, jewelry, and art across nearly every civilization. Gold’s historical value stems from its unchanging quality—it does not rust, tarnish, or corrode like most other metals. This stability raises a fundamental question: does this famously inert substance attract or bond with any other elements?
The Magnetic Status of Gold
The most common way people think about attraction involves magnetism, but pure gold is not attracted to a common magnet. Unlike ferromagnetic metals like iron or nickel, gold exhibits diamagnetism. This means that when exposed to a strong external magnetic field, gold creates a weak magnetic field in the opposite direction.
The reason for this behavior lies in the atomic structure of the gold atom. All electrons within a gold atom are paired, meaning their individual magnetic moments effectively cancel each other out. When a magnetic field is applied, it induces a slight shift in the motion of these paired electrons, generating the tiny opposing force.
For all practical purposes, this diamagnetic repulsion is so weak that it is imperceptible. If a piece of gold jewelry or a coin shows a strong attraction to a magnet, it is a clear indication that it is not pure gold. Such pieces are typically alloys mixed with ferromagnetic metals like iron or cobalt, which overpower gold’s natural repulsion.
Why Gold Resists Chemical Attraction
Gold’s reputation as a “noble metal” stems from its resistance to forming chemical bonds with most substances. It does not react with atmospheric oxygen, which is why it retains its luster and does not tarnish like silver or copper. This chemical inertness also means it is unaffected by water and most common acids.
This stability is rooted in gold’s electronic structure and its physical properties. Gold has a high first ionization energy, which is the energy required to remove an electron from the atom. The atom strongly holds onto its electrons, making it difficult for other substances to chemically oxidize or react with it.
Gold also possesses a high electronegativity for a metal, a characteristic typically found in non-metals. This property indicates a strong tendency to attract electrons, making it less inclined to lose electrons and participate in standard chemical reactions. These combined factors protect gold from the chemical attractions that cause other metals to degrade and corrode.
Specific Elements That Bond With Gold
Despite gold’s resistance, a few powerful exceptions exist where strong attraction or reaction readily occurs. One notable example is mercury, which has a unique physical affinity for gold, a process called amalgamation. When liquid mercury touches gold, the gold dissolves into the mercury to form a pasty alloy known as an amalgam.
This process is not a typical chemical reaction but a physical dissolution, similar to how salt dissolves in water. Historically, this method was used in mining to separate fine gold particles from ore. The mercury essentially “attracts” and collects the gold, which is then recovered by heating the amalgam to evaporate the mercury.
Aqua Regia
A second exception involves aqua regia, a highly corrosive mixture of nitric acid and hydrochloric acid (typically in a one-to-three ratio). Neither acid can dissolve gold alone, but the combination is effective. The nitric acid acts as a powerful oxidizer, converting the solid gold metal into gold ions.
The hydrochloric acid then supplies chloride ions, which complex with the newly formed gold ions. This reaction forms the highly stable tetrachloroaurate anion, which “locks” the gold in solution and prevents the gold ions from reverting back to their metallic state.
Gold Cyanidation
The final and most industrially significant method involves cyanide solutions, such as sodium cyanide, in a process known as gold cyanidation. In the presence of oxygen and water, the cyanide ion forms a strong, soluble complex with gold. This chemical attraction is so potent that it can extract gold even from low-grade ores, dissolving the metal into the solution. The resulting dicyanoaurate complex is stable, allowing for the economical extraction of gold.