45
Rh
102.9
Rhodium
Catalyst for ethanol oxidation: platinum-rhodium clusters on a surface of tin dioxide. This catalyst can split the carbon-carbon bond and obtain energy from ethanol in fuel cells. Photo: BNL
Classification: Rhodium is a transition metal
Color: silvery-white
Atomic weight: 102.9055
State: solid
Melting point: 1963 oC, 2236 K
Boiling point: 3695 oC, 3968 K
Shells: 2,8,18,16,1
Electron configuration: [Kr] 4d8 5s1
Density @ 20oC: 12.4 g/cm3
Atomic volume: 8.3 cm3/mol
Structure: fcc: face-centered cubic
Hardness: 6.0 mohs

Discovery of Rhodium


Rhodium was discovered by William Hyde Wollaston in 1803 in crude platinum ore.

Wollaston removed platinum and palladium from the ore to leave a red salt - sodium rhodium chloride [RhCl6]Na3.12H2O from which he extracted rhodium metal.

The element name comes from the Greek word 'rhodon' meaning rose.








Appearance & Characteristics

Rhodium
Rhodium pin and foil. Photo by Dschwen.
Harmful effects:
Rhodium is considered to be non-toxic. Some of its compounds are highly toxic and carcinogenic.

Characteristics:
Rhodium is a rare, hard, silvery-white, lustrous metal. It is highly reflective and extremely resistant to corrosion. It is not attacked by most acids. Rhodium's salts form rose-colored aqueous solutions.

Uses of Rhodium


The majority of rhodium is used as a catalyst in catalytic converters. It is also used to catalyze industrial processes. Rhodium is used as an alloying agent for hardening and improving the corrosion resistance of platinum and palladium. As a result of its low electrical resistance, low and stable contact resistance, and its stability against corrosion rhodium is used as an electrical contact material. The metal is used in jewelry and for decorations.

Abundance & Isotopes

Abundance earth's crust: 1 part per billion by weight, 0.1 parts per billion by moles
Abundance solar system: 2 parts per billion by weight, 0.02 parts per billion by moles
Cost, pure: $13,000 per 100g
Cost, bulk: $7,000 per 100g

Source: Rhodium occurs in small quantities in ores metals such as platinum, palladium, nickel, silver, and gold. Commercially, it is obtained as a byproduct of refining nickel sulfide ores from Canada.

Isotopes: Rhodium has 24 isotopes whose half-lives are known, with mass numbers from 94 to 117. Of these, only one is stable, 103Rh.

Energies

Specific heat capacity: 0.242 J g-1 K-1
Heat of fusion: 21.50 kJ mol-1
1st ionization energy: 719.8 kJ mol-1
3rd ionization energy: 2996.8 kJ mol-1
Heat of atomization: 556 kJ mol-1
Heat of vaporization: 493.0 kJ mol-1
2nd ionization energy: 1744.4 kJ mol-1
Electron affinity: 109.7 kJ mol-1

Oxidation & Electrons

Shells: 2,8,18,16,1
Minimum oxidation number: -1
Min. common oxidation no.: 0
Electronegativity (Pauling Scale): 2.28
Electron configuration: [Kr] 4d8 5s1
Maximum oxidation number: 6
Max. common oxidation no.: 3
Polarizability volume: 8.6 Å3

Reactions & Compounds

Reaction with air: mild, w/ht, ⇒ Rh2O3
Reaction with 15 M HNO3: none
Oxide(s): RhO2, Rh2O3
Hydride(s): none
Reaction with 6 M HCl: none
Reaction with 6 M NaOH:
Chloride(s): RhCl3

Radius

Atomic radius: 134 pm
Ionic radius (2+ ion): pm
Ionic radius (2- ion): pm
Ionic radius (1+ ion): pm
Ionic radius (3+ ion): 80.5 pm
Ionic radius (1- ion): pm

Conductivity

Thermal conductivity: 150 W m-1 K-1
Electrical conductivity:23 x 106 S m-1


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