Which Elements Are Noble Metals?

Noble metals are chemically inert and inactive especially towards oxygen, so they will not corrode over time. The term "noble metal" means that the metal will not oxidize or react with most acids. Examples of noble metals are gold, silver and all elements of the platinum group including, platinum, palladium, rhodium, ruthenium, osmium and iridium. "Noble metal" and "precious metal" are two distinct groups of metals but they are closely related because their chemical properties are almost the same.

Gold

• Gold is considered to be the most inert metal (i.e., it utterly lacks the usual chemical reaction), making it the noblest of metals. Physicists at the Technical University of Denmark have concluded that gold has the most powerful anti-corrosive property. The metal was tested and researched in order to understand what made the metal so different. It was suggested that gold would not bond with any other molecules, therefore reactive molecules would simply fall right off the metal, never disturbing the gold's surface.

Silver

• Silver is another noble metal. According to ChemistryExplained.com, "Silver only reacts slowly with sulfur compounds and highly concentrated acids." Silver does not react with oxygen, but in the air, after extremely long periods of time, it will react to form silver sulfide. Because silver reacts so little and so slowly, it is considered a noble metal.

Platinum

• Platinum metal has many uses because it comes under the categories of both noble and precious Metals. Platinum is extremely non-reactive with nearly everything. Platinum is best used as a catalyst (i.e., a substance that enables a chemical reaction to proceed at a usually faster rate or under different conditions than otherwise possible) because of its noble metal characteristics. Almost all the platinum used goes toward catalysts.

Palladium

• Palladium is also used as a catalyst. While palladium and platinum are used for many of the same applications, normally one is preferred over the other because of their unique chemical properties. For example, palladium is better at cleaning hydrocarbons from cold engines.

Rhodium

• Rhodium is a good catalyst (80 percent of the rhodium manufactured each year is used as catalyst converters). The down side to rhodium is that it is extremely expensive because of its rarity, so normally other noble metals are used before rhodium. Rhodium is about four times more expensive than platinum.

Ruthenium

• Ruthenium is known for resisting the most highly corrosive situations and reactions. Ruthenium is used in underwater pipes, where corrosion takes place extremely quickly.

Osmium

• Osmium is a useful noble metal because of its density. It has an extremely low density. This allows osmium to be used in situations where other noble metals could not be used. Examples include bearings and record player needles.

Iridium

• Iridium is the least likely metal to corrode, but it is also one of the most expensive and rare metals in the world. Iridium is so rare because it is seldom found in the nature. Iridium has only been found in thin layers of rocks. The scientific community believes that these thin layers were made around the same time dinosaurs became extinct.