Rhodium Chemical & Physical Properties
Rhodium Basic Facts
Atomic Number: 45
Symbol: Rh
Atomic Weight: 102.9055
Discovery: William Wollaston 1803-1804 (England)
Electron Configuration: [Kr] 5s1 4d8
Word Origin: Greek rhodon rose. Rhodium salts yield a rosy-colored solution.
Properties: Rhodium metal is silvery-white. When exposed to red heat, the metal slowly changes in air to the sesquioxide. At higher temperatures it converts back to its elemental form. Rhodium has a higher melting point and lower density than platinum. The melting point of rhodium is 1966 +/-3°C, boiling point 3727 +/-100°C, specific gravity 12.41 (20°C), with a valence of 2, 3, 4, 5, and 6.
Uses: One major use of rhodium is as an alloying agent to harden platinum and palladium. Because it has a low electrical resistance, rhodium is useful as an electrical contact material. Rhodium has a low and stable contact resistance and is highly resistant to corrosion. Plated rhodium is very hard and has a high reflectance, which makes it useful for optical instruments and jewelry. Rhodium is also used as a catalyst in certain reactions.
Sources: Rhodium occurs with other platinum metals in river sands in the Urals and in North and South America. It is found in the copper-nickel sulfide ores of the Sudbury, Ontario region.
Element Classification: Transition Metal
Rhodium Physical Data
Density (g/cc): 12.41
Melting Point (K): 2239
Boiling Point (K): 4000
Appearance: silvery-white, hard metal
Atomic Radius (pm): 134
Atomic Volume (cc/mol): 8.3
Covalent Radius (pm): 125
Ionic Radius: 68 (+3e)
Fusion Heat (kJ/mol): 21.8
Evaporation Heat (kJ/mol): 494
Pauling Negativity Number: 2.28
First Ionizing Energy (kJ/mol): 719.5
Oxidation States: 5, 4, 3, 2, 1, 0
Lattice Structure: Face-Centered Cubic
Lattice Constant (Ã…): 3.800