Gold typically loses electrons when it reacts with other substances, most commonly losing either one or three electrons to form positively charged ions. However, gold is unusual among metals because it can also gain an electron under the right conditions, behaving more like a nonmetal. This dual ability makes gold one of the most chemically interesting elements on the periodic table.
Gold’s Electron Setup
A gold atom has 79 electrons arranged in shells: 2, 8, 18, 32, 18, 1. That single electron sitting alone in the outermost shell is the key player. In most metals, a lone outer electron is easy to strip away, which is why sodium and potassium react so violently with water. Gold, though, holds onto that electron far more tightly than you’d expect for a metal with just one valence electron.
The reason comes down to speed. Gold’s nucleus has 79 protons, and the innermost electrons orbit so close to that massive positive charge that they move at a significant fraction of the speed of light. At those speeds, Einstein’s theory of relativity kicks in: the electrons effectively become heavier and their orbits contract. This relativistic contraction cascades outward and shrinks gold’s outermost orbital by about 23%, pulling that single valence electron much closer to the nucleus. The result is a stronger grip on the electron, which is why gold is so resistant to corrosion and so reluctant to react.
When Gold Loses Electrons
In most chemical reactions, gold loses electrons. Its two most common charged states are +1 (losing one electron) and +3 (losing three electrons), though states of +2, +4, and +5 also exist in certain compounds. The +1 and +3 states dominate everyday chemistry.
Gold’s reluctance to give up electrons is reflected in its extremely high reduction potential: 1.69 volts for the +1 ion and 1.41 volts for the +3 ion. In practical terms, this means gold sits near the very top of the “hard to oxidize” list. Ordinary acids like hydrochloric acid or nitric acid alone can’t pull electrons away from gold. This is why gold jewelry doesn’t tarnish and why gold coins survive centuries underground looking almost new.
Dissolving gold requires a trick. Aqua regia, a mixture of hydrochloric and nitric acid, works because the two acids tag-team the problem. The nitric acid acts as the oxidizer, stripping three electrons from each gold atom. Meanwhile, chloride ions from the hydrochloric acid immediately grab onto the newly formed gold ions, pulling them out of the reaction zone. This keeps the reaction moving forward by preventing gold ions from recapturing their lost electrons. The final product is a gold-chloride complex dissolved in solution.
Gold plating uses the same principle in reverse. Gold ions dissolved in a solution gain electrons at the cathode (the object being plated), depositing a thin layer of metallic gold onto the surface. In this electrochemical process, the gold ions are reduced back to neutral gold atoms by absorbing electrons from an electrical current.
When Gold Gains an Electron
Here’s where gold gets strange. Under certain conditions, gold actually gains an electron to form a negatively charged ion called auride (Au⁻), with an oxidation state of -1. This is remarkably rare for a metal. Most metals never form negative ions because they don’t attract extra electrons strongly enough.
Gold can do this because of its unusually high electronegativity. On the Pauling scale, gold scores 2.54, which is higher than every other metal and even exceeds some nonmetals. For comparison, iron scores 1.83, copper 1.9, and silver 1.93. Gold’s electronegativity is closer to selenium (2.55) than to its fellow metals. That contracted outer orbital, squeezed tight by relativistic effects, creates a surprisingly welcoming spot for an extra electron.
The most famous example is cesium auride (CsAu). When cesium and gold react, cesium hands over its outermost electron to gold, and the result behaves like an ionic salt, similar to table salt. Cesium is one of the most eager electron donors on the periodic table, and gold is just electronegative enough to accept. Relativistic calculations show that this effect increases the amount of charge transferred from cesium to gold by about 0.15 electrons compared to what you’d predict without accounting for relativity.
Why Gold Prefers Losing Over Gaining
Despite its ability to gain an electron, gold overwhelmingly loses electrons in real-world chemistry. The auride ion only forms with the most reactive metals, like cesium and rubidium, which are desperate to shed electrons. In virtually every other chemical environment, gold either stays neutral (its preferred state) or loses one to three electrons.
The practical takeaway: gold is a metal, and metals lose electrons. But gold’s relativistic quirks give it a split personality. Its tightly held outer electron makes it extraordinarily noble and corrosion-resistant. That same tight orbital, paradoxically, also makes gold electronegative enough to occasionally accept an electron from the right partner. No other common metal pulls off both behaviors so cleanly.