Rhodium

Rhodium is a chemical element that is silvery-white, hard and chemically inert transition metal

and a member of the platinum group. It has the chemical symbol Rh and atomic number 45.

Rhodium was discovered in 1803 by William Hyde Wollaston. It is found in platinum ores and is mostly used as a catalyst. Rhodium is usually alloyed with platinum or palladium and applied in high-temperature and corrosion-resistive coatings. Rhodium detectors are used in nuclear reactors to measure the neutron flux level.

Characteristics

Rhodium durable metal that has a high reflectance. Rhodium metal does not normally form an oxide, even when heated. Oxygen is absorbed from the atmosphere at the melting point of rhodium, but on solidification, the Oxygen is released. Rhodium has both a higher melting point and lower density than platinum. It is not attacked by acids, it is completely insoluble in nitric acid and dissolves slightly in aqua regia.

Common oxidation states of rhodium is +3, but oxidation states from +0 to +6 are also observed. Unlike ruthenium and osmium, rhodium forms no volatile oxygen compounds. The known stable oxides include Rh2O3, RhO2, RhO2·xH2O, Na2RhO3, Sr3LiRhO6 and Sr3NaRhO6. Halogen compounds are known in nearly the full range of possible oxidation states. Rhodium(III) chloride, rhodium(IV) fluoride, rhodium(V) fluoride and rhodium(VI) fluoride are some examples. The lower oxidation states are only stable if ligands are present.

Naturally occurring rhodium is composed of only one isotope, 103Rh. The most stable radioisotopes are 101Rh with a half-life of 3.3 years, 102Rh with a half-life of 207 days, 102mRh with a half-life of 2.9 years, and 99Rh with a half-life of 16.1 days. Twenty other radioisotopes have been characterized with atomic weights ranging from 92.926 u (93Rh) to 116.925 u (117Rh). Most of these have half-lives that are less than an hour except 100Rh (half-life: 20.8 hours) and 105Rh (half-life: 35.36 hours). There are also numerous meta states with the most stable being 102mRh (0.141 MeV) with a half-life of about 2.9 years and 101mRh (0.157 MeV) with a half-life of 4.34 days.

The primary decay mode before the only stable isotope, 103Rh, is electron capture and the primary mode after is beta emission. The primary decay product before 103Rh is ruthenium and the primary product after is palladium.

Value

The base value of each unit of ranges between 10 and 15Ð per unit, with up to 3 units being found at any one time.

Presence on Mars: Rare