Rhodium Rhodium Ruthenium Category="Chemical elements"Category="Transition metals"Rh redirects here. For Rhesus factor or Rh factor, see Blood type.

45 Ruthenium ← rhodium → Palladium
Co
↑
Rh
↓
Ir
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periodic table
General
Name, Symbol, Number rhodium, Rh, 45
Chemical series transition metals
Group, Period, Block 9, 5, d
Appearance silvery white metallic
[image]
Atomic mass 102.90550(2) g/mol
Electron configuration [Kr] 4d⁸ 5s¹
Electrons per shell 2, 8, 18, 16, 1
Physical properties
Phase Solid
Density (near r.t.) 12.41 g/cmł
Liquid Density at m.p. 10.7 g/cmł
Melting point 2237 K
(1964 °C, 3567 °F)
Boiling point 3968 K
(3695 °C, 6683 °F)
Heat of fusion 26.59 kJ/mol
Heat of vaporization 494 kJ/mol
Heat capacity (25 °C) 24.98 J/(mol·K)

Vapor pressure
P/Pa 1 10 100 1 k 10 k 100 k
at T/K 2288 2496 2749 3063 3405 3997
Atomic properties
Crystal structure cubic face centered
Oxidation states 2, 3, 4
(Amphoteric oxide)
Electronegativity 2.28 (Pauling scale)
Ionization energies 1st: 719.7 kJ/mol
2nd: 1740 kJ/mol
3rd: 2997 kJ/mol
Atomic radius 135 pm
Atomic radius (calc.) 173 pm
Covalent radius 135 pm
Miscellaneous
Magnetic ordering no data
Electrical resistivity (0 °C) 43.3 nΩ·m
Thermal conductivity (300 K) 150W/(m·K)
Thermal expansion (25 °C) 8.2 µm/(m·K)
Speed of sound (thin rod) (20 °C) 4700 m/s
Young's modulus 275 GPa
Shear modulus 150 GPa
Bulk modulus 380 GPa
Poisson ratio 0.26
Mohs hardness 6.0
Vickers hardness 1246 MPa
Brinell hardness 1100 MPa
CAS registry number 7440-16-6
Notable isotopes

Main article: Isotopes of rhodium
iso NA Half-life DM DE (MeV) DP
⁹⁹Rh syn 16.1 d ε - ⁹⁹Ru
γ 0.089, 0.353,
0.528 -
^101mRh syn 4.34 d ε - ¹⁰¹Ru
IT 0.157 ¹⁰¹Rh
γ 0.306, 0.545 -
¹⁰¹Rh syn 3.3 y ε - ¹⁰¹Ru
γ 0.127, 0.198,
0.325 -
^102mRh syn 2.9 y ε - ¹⁰²Ru
γ 0.475, 0.631,
0.697, 1.046 -
¹⁰²Rh syn 207 d ε - ¹⁰²Ru
β⁺ 0.826, 1.301 ¹⁰²Ru
β^- 1.151 ¹⁰²Pd
γ 0.475, 0.628 -
¹⁰³Rh 100% Rh is stable with 58 neutrons
¹⁰⁵Rh syn 35.36 h β^- 0.247, 0.260,
0.566 ¹⁰⁵Pd
γ 0.306, 0.318 -
References

Rhodium is a Chemical element in the Periodic table that has the symbol Rh and Atomic number 45. A rare silvery-white hard Transition metal, rhodium is a member of the Platinum group, is found in platinum ores and is used in alloys with platinum and as a Catalyst.

Notable characteristics

Rhodium is a hard silvery white and durable metal that has a high reflectance. If slowly cooled from a red hot state it changes in air to the sesquioxide, which at higher temperatures converts back to the metal. Rhodium has both a higher Melting point and lower density than Platinum. It is not attacked by acids and only dissolves in Aqua regia.

Applications

The primary use of this element is as an alloying agent for hardening platinum and Palladium. These alloys are used in furnace windings, bushings for glass fiber production, thermocouple elements, electrodes for aircraft spark plugs, and laboratory crucibles. Other uses;

It is used as an electrical contact material due to its low electrical resistance, low and stable contact resistance, and its high Corrosion resistance.
Plated rhodium, made by Electroplating or evaporation, is extremely hard and is used for optical instruments.
This metal finds use in jewelry and for decorations.
It is also a highly useful Catalyst in a number of industrial processes (notably it is used in the catalytic system of automobile catalytic converters and for catalytic carbonylation of methanol to produce Acetic acid by the Monsanto process).

History

Rhodium (Greek rhodon meaning "rose") was discovered in 1803 by William Hyde Wollaston soon after his discovery of Palladium. Wollaston made this discovery in England using crude Platinum ore that he presumably obtained from South America.

His procedure involved dissolving the ore in Aqua regia, neutralizing the acid with Sodium hydroxide (Na O H). He then precipitated the platinum metal by adding Ammonium chloride, NH₄Cl, as ammonium chloroplatinate. The element palladium was removed as palladium cyanide after treating the solution with mercuric cyanide. The material that remained was a red Rhodium(III) chloride: rhodium metal was isolated via reduction with Hydrogen gas.

Occurrence

The industrial extraction of rhodium is complex as the metal occurs in ores mixed with other metals such as Palladium, Silver, Platinum, and Gold. It is found in platinum ores and obtained free as a white inert metal which it is very difficult to fuse. Principal sources of this element are located in South Africa, in river sands of the Ural Mountains, in North and South America and also in the Copper-nickel sulfide mining area of the Sudbury, Ontario region. Although the quantity at Sudbury is very small, the large amount of nickel ore processed makes rhodium recovery cost effective. Main exporter of rhodium is South Africa (>80%) followed by Russia. However, the annual world production of this element is only about 20 tons and there are very few rhodium minerals.

It is also possible to extract Rhodium from burned-out nuclear fuel, which contains a small percentage of rhodium. Rhodium produced in such a way contains radioactive isotopes with half-lives of up to 45 days and it must be checked very carefully for radioactivity before being sold. Reprocessing of spent nuclear fuel creates a great deal of nuclear waste in the form of radiologically damaged reprocessing equipment, therefore reprocessing would not likely be done for something as "cheap" as rhodium.

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). Most of these have half-lifes that are less than an hour except Rh-100 (half-life: 20.8 hours) and Rh-105 (half-life: 35.36 hours). There are also numerous meta states with the most stable being Rhm-102 (0.141 MeV) with a half-life of about 2.9 years and Rhm-101 (0.157 MeV) with a half-life of 4.34 days.

The primary Decay mode before the only stable isotope, Rh-103, is Electron capture and the primary mode after is beta emission. The primary Decay product before Rh-103 is Ruthenium and the primary product after is Palladium.

Precautions

Compounds that contain rhodium are not often encountered by most people and should be considered to be highly toxic and carcinogenic. Rhodium compounds can stain human skin very strongly. This element plays no biological role in humans.

References

Los Alamos National Laboratory - Rhodium

External links

WebElements.com - Rhodium