Rhodium Facts

Rhodium Chemical & Physical Properties

Science

By

Anne Marie Helmenstine, Ph.D.

Updated on July 03, 2019

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.

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)

Specific Heat (@20°C J/g mol): 0.244

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 (Å): 3.800

References: Los Alamos National Laboratory (2001), Crescent Chemical Company (2001), Lange's Handbook of Chemistry (1952), CRC Handbook of Chemistry & Physics (18th Ed.)

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