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Elemental rhodium [l to r]: 1g powder, 1g pressed cylinder, 1g argon arc remelted pellet.
Image: Alchemist-hp (Creative Commons ‘Attribution-NonCommercial-NonDerivative 3.0 (US)’ license).
This week's element is rhodium, a hard, shiny silvery-white transition metal that is 1000 times scarcer than gold. Rhodium has the atomic symbol Rh and the atomic number 45.
Since there aren't any minerals that contain quantifiable amounts of rhodium, most of the world's rhodium is obtained as a by-product of mining for other, more common, precious metals such as palladium, copper, silver, platinum, and gold. Most rhodium comes from South Africa and most rhodium is used in North America and Europe as catalytic converters in automobiles. Of all the metals, only rhodium can reduce the damaging nitrogen oxide gases in automotive exhaust to gaseous nitrogen and oxygen.
Rhodium is more valuable than any other element on the planet due to its extreme rarity combined with the demand from the automotive industry. Thus, those who invest in rhodium can demand any price they wish for this metal. But it does have other uses, particularly in the jewelry industry, where rhodium plating gives platinum or gold jewelry ("white gold") its lovely gleaming white surface, and protects sterling silver jewelry from tarnishing.
Perhaps the most interesting bit of trivia that I can tell you about rhodium is that, instead of being given a gold or platinum disc, Paul McCartney was given a rhodium-plated disc in 1979 in recognition for being the all-time best selling singer-songwriter.
But that said, I think the most interesting character of rhodium is its peculiar ability to absorb oxygen from the atmosphere without becoming oxidized itself. How does it do this? When melted, rhodium captures oxygen and then releases oxygen when it solidifies.
Here's the Professor to tell us a little more about this extremely rare precious metal:
Visit periodicvideos's YouTube channel [video link].
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Video journalist Brady Haran is the man with the camera and the University of Nottingham is the place with the chemists. You can follow Brady on twitter @periodicvideos and the University of Nottingham on twitter @UniNottingham
You've already met these elements:
Ruthenium: Ru, atomic number 44
Technetium: Tc, atomic number 43
Molybdenum: Mo, atomic number 42
Niobium: Ni, atomic number 41
Zirconium: Zr, atomic number 40
Yttrium: Y, atomic number 39
Strontium: Sr, atomic number 38
Rubidium: Rr, atomic number 37
Krypton: Kr, atomic number 36
Bromine: Br, atomic number 35
Selenium: Se, atomic number 34
Arsenic: As, atomic number 33
Germanium: Ge, atomic number 32
Gallium: Ga, atomic number 31
Zinc: Zn, atomic number 30
Copper: Cu, atomic number 29
Nickel: Ni, atomic number 28
Cobalt: Co, atomic number 27
Iron: Fe, atomic number 26
Manganese: Mn, atomic number 25
Chromium: Cr, atomic number 24
Vanadium: V, atomic number 23
Titanium: Ti, atomic number 22
Scandium: Sc, atomic number 21
Calcium: Ca, atomic number 20
Potassium: K, atomic number 19
Argon: Ar, atomic number 18
Chlorine: Cl, atomic number 17
Sulfur: S, atomic number 16
Phosphorus: P, atomic number 15
Silicon: Si, atomic number 14
Aluminium: Al, atomic number 13
Magnesium: Mg, atomic number 12
Sodium: Na, atomic number 11
Neon: Ne, atomic number 10
Fluorine: F, atomic number 9
Oxygen: O, atomic number 8
Nitrogen: N, atomic number 7
Carbon: C, atomic number 6
Boron: B, atomic number 5
Beryllium: Be, atomic number 4
Lithium: Li, atomic number 3
Helium: He, atomic number 2
Hydrogen: H, atomic number 1
Here's a wonderful interactive Periodic Table of the Elements that is just really really fun to play with!
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