Noble metal
A metal with low chemical reactivity that resists oxidation and corrosion. Gold, platinum, and palladium are prominent examples.
Electrochemical series: A ranking of chemical species by their standard electrode potentials, indicating tendencies to gain or lose electrons. More positive reduction potentials help explain why many noble metals resist oxidation.
Oxidation: A chemical process in which an atom, ion, or molecule loses electrons or increases its oxidation state. Resistance to oxidation is central to the defining behavior of noble metals.
Catalysis: The acceleration of a chemical reaction by a substance that is regenerated rather than consumed overall. Gold, platinum, and palladium catalyze reactions while resisting destructive chemical change.
Alkali metal: An element in Group 1 of the periodic table, excluding hydrogen, characterized by high reactivity and a single valence electron. Alkali metals oxidize readily, nearly reversing the characteristic behavior of noble metals.
Standard electrode potential: The voltage of a redox half-reaction measured relative to the standard hydrogen electrode under standard conditions. It quantifies the reduction tendency used to compare metals’ nobility.
Corrosion: The deterioration of a material through chemical or electrochemical reactions with its environment. Noble metals are valued for resisting this broader class of material damage.
Platinum group metals: Six transition metals—ruthenium, rhodium, palladium, osmium, iridium, and platinum—with related chemical and physical properties. Several members combine corrosion resistance with strong catalytic performance.
Base metal: A common metal that oxidizes or corrodes relatively readily, often contrasted with precious or noble metals. Base metals provide the practical chemical contrast to corrosion-resistant noble metals.
Galvanic corrosion: Accelerated corrosion that occurs when dissimilar electrically connected metals are exposed to an electrolyte. A noble metal can drive corrosion of a less noble metal in electrical contact.
Redox: A class of chemical reactions involving the transfer of electrons between species. Nobility describes a metal’s behavior within oxidation–reduction reactions.