The question of whether gold is positive or negative cannot be answered with a single word, as the charge depends entirely on the context. Gold (Au) is a noble metal, and its electrical state changes dramatically depending on whether it exists in its pure metallic form, as a dissolved ion in a chemical solution, or as a component in a compound. In chemical reactions, gold typically loses electrons to become positively charged, while in its physical state, the metal is electrically neutral.
Gold’s Common Oxidation States
When gold engages in chemical bonding, it generally gives up electrons to form a positive ion, known as a cation. This oxidation process results in the gold atom having a positive charge, allowing it to bond with negatively charged ions. The most frequently observed oxidation states for gold in its compounds are +1 and +3.
The +1 state is called the aurous ion, while the +3 state is referred to as the auric ion. For instance, in gold(III) chloride, the gold atom loses three electrons to achieve the +3 state, forming a chemical bond with three chlorine atoms.
In rare and highly specific chemical environments, gold can exhibit a negative charge, an oxidation state of -1. This negative ion, known as an auride, forms only when gold is combined with highly electropositive metals, such as caesium or rubidium, in compounds like caesium auride (\(\text{CsAu}\)). These auride compounds are chemically unusual and extremely unstable in the presence of water or air.
Gold’s Tendency to Gain Electrons
Gold’s resistance to corrosion is explained by electrochemistry. Gold is classified as a noble metal because it has a very high positive standard reduction potential, which measures a chemical species’ tendency to be reduced (gaining electrons).
For a gold ion (\(\text{Au}^{3+}\)) to become the neutral metal (\(\text{Au}\)), it must gain three electrons. This reduction reaction has a highly positive potential, approximately \(+1.42\) volts. This large positive value signifies that the reaction \(\text{Au}^{3+} \rightarrow \text{Au}\) is highly favored and occurs spontaneously.
The reverse reaction, the oxidation of the neutral gold metal (\(\text{Au}\)) to form a positive ion (\(\text{Au}^{3+}\)), has a negative potential, indicating it is not spontaneous and is difficult to achieve. This resistance to oxidation is precisely why gold remains untarnished and is found in its elemental state in nature.
The Electrical State of Bulk Gold
When considering a piece of gold jewelry or a gold bar, the metal is electrically neutral, possessing neither a net positive nor a net negative charge. This is because bulk gold metal contains an equal number of positively charged protons within the nucleus of each atom and negatively charged electrons surrounding them.
The atomic structure of gold, a face-centered cubic lattice, allows its outermost electrons to detach from individual atoms and form a shared “sea of electrons” that moves freely throughout the metal structure. This free movement of electrons makes gold an excellent conductor of electricity, surpassed only by silver and copper.
The electrical neutrality of gold is a significant advantage in electronics, where it is often used for connectors and circuit boards. Gold’s lack of chemical reactivity prevents it from forming an insulating layer of tarnish or rust, ensuring that its conductive properties remain consistent and reliable over long periods.