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).