Rhodium

Atomic Number:

45

Melting Point: 1964 ºC
Atomic Symbol: Rh Boiling Point:  3695 ºC 
Atomic Weight: 102.9055 amu Density: 12450 kg/m 3
Atomic Radius:

134.5 pm

Oxidation States: 3
Covalent Radius: 135 pm Electron Configuration: [Kr]5s14d8
van der Waals Radius:

--

State of Matter: solid 

History

(Gr. rhodon: rose) Wollaston discovered rhodium between 1803 and 1804 in crude platinum ore he presumably obtained from South America.

Properties

The metal is silvery white and at red heat slowly changes in air to the resquioxide. At higher temperatures it converts back to the element. Rhodium has a higher melting point and lower density than platinum. It is highly reflective, hard, and durable.

Sources

Rhodium occurs natively with other platinum metals in river sands of the Urals and in North and South America. It is also found with other platinum metals in the copper-nickel sulfide area of the Sudbury, Ontario region. Although the quantity occurring there is very small, the large tonnages of nickel processed make the recovery commercially feasible. The annual world production of rhodium is only 7 or 8 tons.

Uses

Rhodium's primary use is as an alloying agent to harden platinum and palladium. Such alloys are used for furnace windings, thermo coupling elements, bushings for glass fiber production, electrodes for aircraft spark plugs, and laboratory crucibles. It is useful as an electrical contact material as it has a low electrical resistance, a low and stable contact resistance, and is highly resistant to corrosion. Plated rhodium, produced by electroplating or evaporation, is exceptionally hard and is used for optical instruments. Rhodium is also used for jewelry, for decoration, and as a catalyst.

Isotopes

Naturally occurring rhodium is composed of only one isotope (Rh-103). The most stable radioisotopes are Rh-101 with a half-life of 3.3 years, Rh-102 with a half-life of 207 days, and Rh-99 with a half-life of 16.1 days. Twenty other radioisotopes have been characterized with atomic weights ranging from 92.926 u (Rh-93) to 116.925 u (Rh-117). There are also numerous meta states.

Hazards

Compounds that contain rhodium are not often encountered by most people but should be considered to be highly toxic and carcinogenic. Rhodium compounds can stain human skin very strongly. Exposure to rhodium (metal fume and dust, as Rh) should not exceed 1 mg/m^3 (8-hour time-weighted average, 40-hour week).