Scandium

Category: transition metal Atomic number: 21 Colour: silvery white Melting point: 1,541°C (2,806°F) Boiling point: 2,836°C (5,136°F) First identified: 1879

Mendeleev left four notable gaps in his periodic table and speculated that an element would eventually be discovered to fill each of them. He gave the missing elements names based on their proximity to other known substances – in his original table, boron was at the top of group 3, and in the space for an element with an atomic number of 21 beneath that he added ‘eka-boron’ (by which he meant ‘one place away from boron’). Boron was eventually moved to the top of group 13, but within a decade of the first publication of Mendeleev’s table, the discovery of scandium, filling the ‘eka-boron’ space which was now top of group 3, helped to solidify his reputation and to focus worldwide attention on his work. (Gallium had already filled the first gap when it was discovered in 1875 – see here.)

The Swedish chemist Lars Fredrik Nilson managed to isolate a tiny sample of scandium oxide from the mineral euxenite in 1879, although it would take until 1937 for a larger sample of the (nearly) pure metal to be extracted from ores. It was named after Scandinavia, where it had been found. It is rare – global production is still only about ten tons a year. This makes it considerably more valuable than gold, but it is mainly mined for industrial purposes rather than being traded as a luxury metal. It is a light element that produces excellent alloys, with aluminium in particular – these are used in lightweight sports equipment and aircraft. Scandium has also been used, in the form of scandium iodide, in high-performance floodlights.

While scandium is rare on Earth, it is more common elsewhere in the universe – both the sun and the moon have higher concentrations of the metal than our planet.