Rhodium
Definition and meaning of Rhodium in chemistry.
Rhodium is a rare, silvery-white, hard, and extremely corrosion-resistant transition metal with the chemical symbol Rh and an atomic number of 45. It is a prominent member of the platinum group metals and is celebrated commercially as one of the most valuable and expensive precious metals on Earth.
In more detail
Positioned in group 9 and period 5 of the periodic table, rhodium occurs naturally alongside other platinum group metals in river sands and in complex nickel-copper sulfide ores. This noble metal is highly inert chemically, showing absolutely no reaction to oxygen at standard room temperature and demonstrating complete resistance to attack by most potent acids, including aqua regia. It possesses a remarkably high optical reflectance and exceptional physical hardness, which inherently prevents tarnishing and scratching under normal environmental and wear conditions. Rhodium usually exhibits a primary oxidation state of +3 in its varied coordination compounds, acting as an exceptional transition metal catalyst for industrial chemical reactions like the large-scale synthesis of acetic acid from methanol. Because of its extreme geological scarcity and unique, irreplaceable catalytic properties for reducing toxic nitrogen oxides into harmless nitrogen gas, its fluctuating market price frequently exceeds that of both gold and pure platinum.
Key facts
| Field | General Chemistry |
|---|---|
| Symbol | Rh |
| Atomic number | 45 |
| Atomic mass | 102.91 u |
| Category | Transition Metal |
| State at room temperature | Solid |
| Melting point | 1964 °C |
| Boiling point | 3695 °C |
| Year discovered | 1803 |
The vast majority of global rhodium production is utilized in the manufacturing of three-way catalytic converters for automobiles, where it critically helps reduce toxic emissions of nitrogen oxides from exhaust gases.
Frequently asked questions
Why is rhodium used to plate jewelry?
Rhodium plating provides a highly reflective, brilliant white finish that effectively resists tarnishing and scratching, and is overwhelmingly used to coat white gold and silver pieces.
Why is rhodium so expensive?
Its exceptionally high price is driven directly by its extreme rarity in the Earth's crust combined with massive, inelastic demand from the automotive industry for emission control systems.