Rhodium
Element 45 · Transition Metal
Rhodium is a brilliant silvery-white metal that is harder than platinum and almost completely immune to tarnish. Its greatest claim to fame is inside the catalytic converter of nearly every gasoline car, where rhodium helps convert toxic nitrogen oxides in exhaust into harmless nitrogen gas. The same reflectivity and corrosion resistance make it the standard plating for white-gold jewelry — the bright finish on most 'white gold' rings is actually a thin coat of rhodium. Its name comes from the Greek word for rose, after the rose-red color of one of its salts.
Key facts
| Atomic number | 45 |
|---|---|
| Atomic weight | 102.91 |
| Category | Transition Metal |
| Group / Period | 9 / 5 |
| Block | d |
| Electron configuration | [Kr] 4d8 5s1 |
| Common oxidation states | +3, +1 |
| State at STP | Solid |
| Electronegativity | 2.28 |
| Atomic radius | 134 pm (empirical) |
| Density | 12.41 g/cm³ |
| Melting point | 1964 °C |
| Boiling point | 3695 °C |
Occurrence
Rhodium is among the rarest elements in Earth's crust. It is found with platinum-group ores, chiefly in South Africa, and is extracted during platinum refining rather than mined for itself.
Applications
Catalytic converters for vehicles
Jewelry plating (rhodium plating)
Reflective optical coatings
Chemical catalysts
Common compounds
- Rhodium chloride
- Rhodium oxide
Rhodium is one of the rarest and most expensive precious metals on Earth — most of the world's supply arrives as a by-product of platinum mining in South Africa.
Data source: IUPAC standard atomic weights 2021; NIST physical property data