Yes, rhodium is a transition metal. It sits in Group 9, Period 5 of the periodic table, squarely in the d-block where all transition metals are found. Its electrons partially fill the 4d orbital, which is the defining feature of a transition metal. Rhodium is also one of six platinum group metals, a family known for extreme rarity, corrosion resistance, and catalytic ability.
Why Rhodium Qualifies as a Transition Metal
The periodic table organizes elements into blocks based on which type of electron orbital is being filled. Transition metals occupy the d-block, meaning their outermost electrons sit in d orbitals. Rhodium’s ground-state electron configuration places electrons in the 4d orbital, and it can exist in multiple oxidation states, from +1 all the way up to +7 in exotic laboratory conditions. That ability to shift between oxidation states is a hallmark of transition metals and the reason they’re so useful as catalysts.
The most common oxidation states you’ll encounter for rhodium are +1 and +3, though researchers have confirmed +5, +6, and even +7 in specialized compounds. A 2022 study published through the National Center for Biotechnology Information identified a rhodium(VII) cation for the first time, pushing the known chemistry of this element further than previously thought.
Physical Properties
Rhodium is a silvery-white metal that is hard, dense, and extremely reflective. It melts at about 1,964°C (3,571°F), which is typical of transition metals with strong metallic bonding. Its density is 12.41 g/cm³, making it roughly 50% denser than lead. It resists corrosion and does not tarnish in air, even at high temperatures.
That reflectivity is one of rhodium’s most commercially useful traits. It reflects visible light better than almost any other metal, which is why it’s used as a finishing coat on jewelry and mirrors.
How Rhodium Is Used
The single biggest use for rhodium is in catalytic converters, the emission-control devices fitted to car exhaust systems. Rhodium’s job inside the converter is to break apart nitrogen oxides, pollutants that contribute to smog and acid rain. It does this through a stepwise process: nitrogen dioxide is first reduced to nitric oxide, then to nitrous oxide, and finally to harmless nitrogen gas and water. The critical step happens when two nitric oxide molecules bond together on the rhodium surface, forming an intermediate compound that then breaks down to release nitrogen. This catalytic ability, driven by rhodium’s flexible oxidation states, is a textbook example of why transition metals dominate industrial chemistry.
In jewelry, rhodium is electroplated onto white gold and silver to give them a brighter, more durable finish. The plating is thin, typically 0.75 to 1.0 microns for jewelry, but rhodium’s hardness provides genuine scratch resistance and prevents tarnishing. A thinner coat (as little as 0.1 microns) is sometimes used for decorative items, though it won’t last as long or look quite as lustrous.
Rarity and Cost
Rhodium is considered one of the rarest and most valuable precious metals on Earth. Global mine production in 2024 totaled roughly 714,000 troy ounces, with South Africa dominating at about 586,000 ounces, roughly 82% of the world supply. Russia, Zimbabwe, and Canada account for most of the rest. Rhodium is never mined on its own. It occurs alongside platinum and palladium in the same ore deposits and is extracted as a co-product.
That scarcity makes the price volatile. Rhodium hit an all-time high of $29,800 per troy ounce in March 2021, driven by tightening emissions regulations and supply constraints. As of early 2026, it trades around $11,950 per ounce. For context, gold typically trades between $1,800 and $2,600 per ounce over recent years, making rhodium several times more expensive.
Discovery
English chemist William Hyde Wollaston discovered rhodium in 1803 while working with crude platinum ore. He dissolved the ore in a mixture of hydrochloric and nitric acids, removed platinum and palladium through chemical precipitation, and was left with a red residue. That color gave the element its name, from the Greek word “rhodon,” meaning rose. He isolated the pure metal by reducing the rhodium chloride salts with hydrogen gas.
Health and Safety Considerations
In its solid metallic form, rhodium is biologically inert and poses no risk to people who wear rhodium-plated jewelry. Occupational exposure becomes a concern only in industrial settings where rhodium dust or fumes are generated. U.S. workplace limits set by both OSHA and NIOSH cap airborne exposure at 0.1 mg per cubic meter of air over an eight-hour workday. There is limited inhalation toxicity data for rhodium compounds in humans, so these limits are based largely on animal studies and are considered conservative.