Quick Facts
| Property | Value |
|---|---|
| Symbol | Rh |
| Atomic Number | 45 |
| Atomic Mass | 102.91 u |
| Category | Transition Metal |
| Period | 5 |
| Group | 9 |
| Block | d |
| Electron Configuration | [Kr] 4d⁸ 5s¹ |
Physical Properties
| Property | Value |
|---|---|
| State at 20°C | Solid |
| Density | 12.41 g/cm³ |
| Melting Point | 1964°C (2237 K) |
| Boiling Point | 3695°C (3968 K) |
| Appearance | Silvery-white, hard metal |
Atomic Properties
| Property | Value |
|---|---|
| Electron Configuration | [Kr] 4d⁸ 5s¹ |
| Electronegativity | 2.28 (Pauling scale) |
| First Ionization Energy | 719.7 kJ/mol |
| Atomic Radius | 134 pm |
| Covalent Radius | 142 pm |
| Van der Waals Radius | 195 pm |
History and Discovery
Discovered by: William Hyde Wollaston Year of Discovery: 1803 Location: London, England
Etymology
Named from the Greek "rhodon" meaning "rose," due to the rose-red color of its chloride compounds.
Discovery Story
William Hyde Wollaston discovered rhodium in 1803 while working with crude platinum ore from South America. He dissolved the ore in aqua regia, precipitated the platinum, and then identified rhodium in the residue by its distinctive rose-colored salts.
Isotopes
| Isotope | Natural Abundance | Half-life | Decay Mode |
|---|---|---|---|
| ¹⁰³Rh | 100% | Stable | - |
Occurrence
Natural Abundance
Rhodium is extremely rare, comprising only about 0.0001 ppm of Earth's crust (one of the rarest elements). It is found with platinum ores and as a native alloy. Major sources are South Africa (about 80% of production), Russia, and Zimbabwe.
Extraction and Production
- Byproduct: From platinum and nickel mining
- Complex Refining: Chemical separation from other PGMs
- Sources: Primarily South Africa
- Global production: about 25-30 tons annually
Applications and Uses
Automotive Catalysts
- Three-way catalytic converters (main use—about 80%)
- Reduces NOx emissions
- Most effective catalyst for NOx reduction
Industrial Catalysts
- Nitric acid production
- Acetic acid production
- Hydrogenation reactions
Electrical Applications
- Electrical contacts
- Spark plug electrodes
Other Uses
- Rhodium plating (jewelry, mirrors)
- High-reflectance mirrors
- Thermocouples
- Crucibles for growing crystals
Biological Role
Rhodium has no known biological role and is not essential for any organism.
In the Human Body
Rhodium is not normally present in the body. It has very low toxicity due to its chemical inertness.
Safety and Hazards
Toxicity
Rhodium metal is considered non-toxic. Most rhodium compounds have low toxicity. However, limited data exists.
Handling Precautions
- Generally considered safe to handle
- Dust may be irritating
- Some compounds may cause allergic reactions
- Standard precious metal handling procedures
Environmental Impact
Rhodium is released from catalytic converters at very low levels. It may accumulate near roadways but concentrations remain very low.
Interesting Facts
- Rhodium is the most expensive precious metal, often exceeding $10,000/oz
- About 80% of global rhodium goes into automotive catalytic converters
- It has no known biological function in any organism
- Rhodium is so rare that annual production would fit in a small room
- William Wollaston kept his discovery method secret for 20 years to profit from it