You may have seen the news that the planet Venus passed across the sun today in an event that will not be seen again for another 105 years. Such a rare astronomical event got me thinking, is there anything in chemistry that is as rare?
Quite simply, no! However, there are the rare earth elements. These are a set of elements more commonly classified as the Lanthanides plus Scandium & Yttrium. Strangely though, the rare earth elements are not actually very rare! They were named rare earth elements as they were originally discovered in the late 18th and 19th Century in scarce minerals dug up from mines.
The majority of the Rare Earth Elements exist in the Lanthanide series of elements at the bottom of the periodic table. Lanthanides have a very different electronic configuration, which gives them some amazing properties. You have probably learnt that elements fill their electron shells from the inside, out. Meaning that the first shell contains 2 electrons, second shell 8 and so on. The Lanthanides are special because as you go across the period, the electrons actually fill an inner shell (the 4-f shell) these electrons are “shielded” by the outer electrons and don’t take part in any bonding.
Because of this, the elements have some fantastic properties which include some fascinating light emission and magnetism properties. These properties allow the elements to be used in a wide variety of applications. You may be amazed to hear that your hard drives contain a neodymium magnet which allows you to access all of your tunes and files, the same element is used in wind turbines as the magnet which generates electricity to power your flat screen TV’s and mobile phones, which incidental contain terbium and europium, (more rare earth elements) who’s light emitting properties allow us to use them in screens.
Rare Earth Elements in a bit more detail …
It is the partially filled f-orbitals which means that when we excite (give energy to) these elements there is a space for lower energy f-electrons to be excited to. When these electrons are excited they can relax back to a lower energy and release a photon of light.
This amazing property means that you can also find rare earth elements in lasers, energy-saving light bulbs, and display screens.
Rare earth elements are becoming particularly useful in green chemistry applications, like many of the transition metals they can make fantastic catalysts. This is due to the very large ionic radius of rare earth elements allowing very high co-ordination numbers. They can also support several different oxidation states which can be very useful for supporting REDOX reactions. By using rare earth elements as catalysts synthetic routes with higher atom economies can be found and used to create more efficient and greener reactions.
Recently there have been several problems reported with the current usage of rare earth elements as 97% of the worlds supplies of these rare earth elements are mined in China and in 2010 the Chinese government decided to cut the amount of rare earth elements it exports. Because of these restrictions the price of rare earth elements has risen very sharply over the last few years. One of the problems is that to recycle many of the rare earth elements used to make magnets involves melting the magnets to a very high temperature, this so far has not been economically viable.
Rare earth elements are becoming more and more important and valuable in the modern world and if the 20th century becomes the age of oil or silicon, the 21st may well become known the age of rare earth metals.