An Overview about the Chemical Element Rhodium


Symbol: Rh

Atomic Number: 45

Atomic Mass: 102.9055 amu (atomic mass units)

Melting Point: 1966.0 C (2239.15 K, 3570.8 F)

Boiling Point: 3727.0 C (4000.15 K, 6740.6 F)

Number of Protons: 45

Number of Electrons: 45

Number of Neutrons: 58

Classification: Transition Metal or precious metal or platinum group metal

Crystal Structure: Cubic

Density @ 293 K: 12.41 grams per cubic centimeter

Color: silver

In 1803 the English chemist William Hyde Wollaston was working on a sample of platinum ore obtained from South America. He dissolved the ore in a mixture of hydrochloric and nitric acids known as aqua regia. He then neutralized the acid with sodium hydroxide before precipitating the platinum in the form of ammonium chloroplatinate by the addition of ammonium chloride. The treatment of the remainder with mercuric cyanide yielded the first of two newly discovered elements, palladium, in the form of palladium cyanide. After these two elements had been extracted there remained a dark red colored material. This was the second of the newly discovered elements, rhodium, in the form of sodium rhodium chloride. The pure metal was obtained from this salt by reduction using hydrogen. The name rhodium relates to the color of the salts of the element and comes from the Greek “rhodon” which means rose.

Rhodium along with osmium, ruthenium, palladium, iridium, and platinum form a group of elements known as the platinum group metals. It is a hard durable metal with a high reflectance. When heated to red heat it forms an oxide but when heated above that temperature it returns to the elemental form.

In nature the element exists as the stable isotope rhodium-103. Over fifty unstable isotopes of rhodium have been identified. The half-lives of these isotopes range from about 150 nanoseconds to 2.9 years.

Rhodium is difficult to extract and purify on an industrial scale as rhodium ores also contain other metals. Rhodium is sometimes produced as a byproduct from the extraction of palladium, silver, platinum, and gold. At other times it may be the primary product of the extraction process.

Rhodium has a number of very important and valuable industrial uses.

* Part of the catalytic converter used in the automobile industry to reduce emissions from exhaust gases.

* Used as an industrial catalyst.

* Production of jewelry.

* Its low resistance and ability to withstand corrosion lead to it being used as electrical contact material.

* Rhodium plate is very hard and is used on optical instruments. They are plated by electroplating or evaporation.

Rhodium is used as an alloy to harden platinum and palladium. These alloys have a number of uses.

* Thermocouple elements.

* Furnace windings.

* Electrodes in aircraft spark-plugs

* Crucibles used in laboratories.

* Bushings used in the production of glass fiber.