The elements with atomic numbers 57-70 are known collectively as the lanthanides, after the first member of the series, lanthanum. The name is derived from the greek word lanthano, meaning, "to lie hidden". The older name was rare-earth elements, although not all are rare.
The discovery of the lanthanides began with yttrium, which is not a rare-earth element but is very similar to them and often found with them. The mineral gadolinite, from which yttrium was first extracted, also contains trace amounts of several lanthanides.
Lanthanide elements with even atomic numbers are more abundant than those with odd numbers, a common feature of all the elements. The cost of lanthanide metals is in line with their rarity: most command prices of several thousand US dollars per kilogram. World reserves of lanthanide metals are estimated to exceed 110 million tons. The largest deposit is in China, and accounts for 75% of world production.
Today, we focus on the first three lanthanides...
Atomic Symbol: La
Atomic Number: 57
Discovered in January 1839 in Stockholm, Sweden by Carl Gustav Mosander, who remained strangely silent about his discovery and did not publish an account of it for several years. Most of his time was taken up running a mineral water business.
Lanthanum is one of the more abundant rare earth elements, being more common than either lead or tin. The element consists of two isotopes, the heavier of which comprises 99.9% of the total. The remaining 0.1%, lanthanum-138, is very weakly radioactive, with a half-life of 100 billion years.
Atomic Symbol: Ce
Atomic Number: 58
There is only a small demand for cerium metal. One use is in so called "self cleaning" ovens, in which it is sprayed on the walls to catalyze the disintegration of cooking residue, which is mostly carbon.
Cerium has some environmentally friendly characteristics: cerium oxide cleans up vehicle exhaust, and cerium is an essential part of long life, low energy light bulbs.
Atomic symbol: Pr
Atomic Number: 59
Carl Mosander believed he discovered two elements, which he named lanthanum and didymium. The first of these was a true element, the second was not, although it was accepted as such for more than 40 years.
Didymium was later discovered to be a mixture of two components: praseodymium and neodymium.
Praseodymium glass is used to make goggles for welders because it filters out heat radiation. It is one of the most abundant rare-earth elements, and is four times more abundant than tin.
There's a terrific book about all the elements called Nature's Building Blocks: An A-Z Guide to the Elements, by John Emsley. Highly recommended if you're one of the statistically insignificant number of people who's interested in this sort of thing.
For more geeky fun, check out my posts on the previous elements, hydrogen through barium, by clicking here.