mol-1 Atomic: Oxidation States: -1, 1, 2, 3, 4, 5 Electronegativity: 2.54 (Pauling scale) Atomic Radius: 144 picometre Covalent Radius: 136 6 picometre Van der Waals Radius: 166 picometre Ionization Energies: 890.1 kJ.mol-1 (first), 1980 kJ.mol-1 (second) The term "gold" was derived from "geolu", an Old English Anglo-Saxon word which means "yellow". The American Silver Eagle and the Mexican Silver Libertad bullion coins, introduced in 1986 and 1982 respectively, were made of 99.9% silver and 0.1% copper. Other notable silver bullion coins include the Australian Silver Kookaburra, Chinese Silver Panda, and the Russian George the Victorious. Minting coins, whether gold or silver, always entails the risk of having the value of the metal used in the coin greater than the coin's face value. Before the turn of the 20th century, countries that were still on silver standard started pegging their monetary units to the gold standard of either the United States or the United Kingdom. For example, Mexico, the Philippines, and Japan pegged their respective silver units to the U.S. dollar at fifty cents. cm-3 Melting Point: 1554.9 C, 2830.82 F, 1828.05 K Boiling Point: 2963 C, 5365 F, 3236 K Heat of Fusion: 16.74 kJ.mol-1 Heat of Vaporization: 362 kJ.mol-1 Atomic: Oxidation States: 0, +1, +2, +4, +6 Electronegativity: 2.2 (Pauling scale) Atomic Radius: 137 picometre Covalent Radius: 139 6 picometre Van der Waals Radius: 163 picometre Ionization Energies: 804.4 kJ. Other countries later began issuing their own palladium bullion coins, including Canada (with its Big & Little Bear Constellations and the very popular Palladium Maple Leaf), Australia, France, China, Portugal, and the former Soviet Union. The latter, in fact, is known to have minted the most number of palladium coins in the world. Its principal use is for electrical purposes, mainly because of its density and its high resistance to corrosion even at extremely high temperatures. Iridium is considered the fourth least abundant element in the Earth's crust, after rhenium, ruthenium, and rhodium. Its price is estimated to be about USD408 per troy ounce (USD13,117 per kilogram) as of January 2010.