Greetings, and welcome to the fourth instalment of the Element of the Month – a regular feature on the Radleys blog. To choose the element of the month, we use a random number generator to produce a figure between 1 and 118 – the current number of elements in the periodic table. This month, we drew the number 45, making rhodium our fourth element of the month. Rhodium – The Key Facts Rhodium has the chemical symbol Rh, the atomic number 45, and is one of the six platinum group metals (the others being platinum, palladium, osmium, iridium and ruthenium). Highly reflective, this silvery white, lustrous and hard metal is a noble metal often found in platinum and nickel ores. Eight Fascinating Facts about Rhodium Rhodium was discovered in 1803 by William Hyde Wollaston (who also discovered palladium), while he was experimenting with platinum ores in South America. He named rhodium after the rosy tint of one of its chlorine compounds, which was produced from its reaction with aqua regia. Rhodium only has a single naturally occurring isotope (103Rh). However, there are 25 radioactive isotopes of rhodium, eighteen of which have half-lives of less than an hour. In contrast with the other group 9 elements, rhodium has just one electron in its outer shell. Being one of the rarest elements in the earth’s crust (only making up 0.0002 parts per million), rhodium is one of the most valuable of the precious metals. This scarcity affects the price of rhodium and thus its usage in commercial applications. 80% of rhodium’s commercial use is as one of the catalysts in three-way catalytic converters in automobiles. (This usage was introduced by Volvo in 1976.) This practice helps to convert carbon monoxide, unburned hydrocarbons and nitrogen oxide into safer gases, reducing the harmful emissions from vehicles. Due to its low electrical resistance and its high resistance to corrosion, rhodium is used as an electrical contact material. Rhodium is also used in the jewellery industry due to its highly reflective and durable surface: white gold and silver are often plated with rhodium to improve their appearance or to prevent tarnishing respectively, known as rhodium flashing. In 1979, in honour of his achievements as history’s all time best-selling songwriter and recording artist, Paul McCartney was awarded a rhodium-plated disc, as other metals (such as gold, silver and platinum) were deemed to be insufficient. And that is rhodium, one of the most precious metals on earth, our fourth Element of the Month. Come back next month, when we’ll be getting rather excited about sodium.