The elements from lanthanum to ytterbium are known collectively as lanthanides or rare-earth elements. The term rare-earth elements is a misnomer because some are not rare at all. The minerals from which they are extracted are actually quite common. The mineral monazite is mined worldwide, and it contains a complex mixture of nearly all the lanthanide elements.
My last chemistry post discussed the first three lanthanide metals. Today's will cover the next three. Please enjoy...
Atomic Symbol: Nd
Atomic Number: 60
This is the best known of all the rare-earth elements because of neodymium magnets. These are by far the strongest magnets available, so strong that they are genuinely dangerous to be around, especially if you have more than one. They fly together which such force that they can shatter and send splinters in all directions, and can jump at each other from more than a foot away. Even very small ones can crush a finger, large ones an entire hand. They are used in fake magnetic piercings, which sometimes become impossible to pull apart, requiring a hospital visit for surgical removal.
Neodymium magnets are also used to check for counterfeit currency by detecting the magnetic particles in the ink used to print real currency.
Atomic Symbol: Pm
Atomic Number: 61
There is no way that this element could be successfully extracted from terrestrial sources. Promethium is radioactive with a half-life too short to have survived from when the earth was formed. The longest lived isotope has a half-life of only 17.7 years.
Promethium is obtained in minute quantities from the fission products of nuclear reactors. Its commercial applications are very meager: it was briefly used to create luminous dials for watches, but was soon replaced because its half-life made the glowing dials wear out too quickly to be practical.
Atomic Symbol: Sm
Atomic Number: 62
Surprisingly, samarium is not named for the ancient city of Samaria, but rather for its discoverer, the Russian scientist Vasili Samarsky-Bykhovets.
One of the strangest compounds on earth is samarium sulfide. It exists as a black crystal, but if scratched, it immediately transforms into a golden crystal with the properties of a metal.
Neodymium magnets are the strongest available, but samarium magnets can operate at higher temperatures where others would lose their magnetism.
A favorite book of mine which has been invaluable in writing these chemistry posts is Nature's Building Blocks: An A-Z Guide to the Elements, by John Emsley. A great recent addition is The Elements: A Visual Exploration, by Theodore Gray, which includes a lot of nice pictures and is suitable for a coffee table near you.
For my previous posts on the elements, click here.