You say tomato, I say tomahto. You say lanthanide, I say lanthanoid. Did anyone think Amy made a mistake tonight when she said lanthanoid, not lanthanide? If so, then stay after school to clean the erasers because Amy was right. The IUPAC, the International Union of Pure and Applied Chemistry, won’t stand for it. Despite 90% of scientific literature using lanthanide the ever-vigilant folks at the IUPAC want us to use lanthanoid. And The Big Bang Theory does its part to educate the public.
The lanthanoid series of elements is that special part of the periodic table that doesn’t fit horizontally so is usually put at the bottom. The defining characteristic of an element is the number of protons in its atomic nucleus. If you are an atom with 57-71 protons, then congratulations, you are a lanthanoid. From lanthanum to lutetium these elements have room for up to 14 electrons to fill an oddly shaped shell around the atomic nucleus (called the “f-shell”). The strange shape of their orbits make the lanthanoids the under-appreciated miracle workers of modern technology.
Lanthanoids make The Big Bang Theory television show possible. Theatrical lighting needs to be bright and just the right color. Lanthanum (57 protons) and cerium (58 protons) rods in arc lamps are extremely popular on Hollywood sets. Praseodymium (59 protons) in aircraft engines strengthens the metals and bring special guest stars to Burbank Airport. Neodymium (60 protons) and samarium (62 protons) make the highest strength permanent magnets. Such magnets are likely found in your TV speakers or headphones. OK, I doubt we use promethium (61 protons) on set, which is always radioactive. If not for europium (63 protons), we’d still be watching Big Bang Theory in black & white, missing a key element in the red phosphors that made color TV first possible in the 1960s. And without gadolinium (64 protons) and terbium (65 protons) there would have been no green. The show could not be edited if all its high-definition data could not be stored on a hard drive using, you guessed it, the easy magnetization properties of dysprosium (66 protons). However without holmium (67 protons), the show could go on. If you watch The Big Bang Theory online, chances are it comes to you on a fiber optic loaded with erbium (68 protons), an optical amplifier. I confess that the next thulium (69 protons) embargo might not be a show-stopper. Ytterbium (70 protons) changes its electrical properties under strain and is a key element for monitoring earthquakes; living in Southern California, we like our ytterbium. And finally lutetium (71 protons), well, its f-shell is full, so one could argue it shouldn’t be a lanthanoid at all.
Why are their names so unfamiliar? The fact that the lanthanoids sometimes go by the name rare earths might give you a clue. It might, but it doesn’t. The lanthanoids are not particularly rare in the Earth’s crust. And the word earth originally meant that their oxides were highly alkali and water-insoluble. Except they are not. You’d think IUPAC would be happy that we at least we’ve mostly stopped calling them rare earths.
But the members of IUPAC are not an easily placated lot. In English, the suffix -ide, is already reserved in chemistry for an element that has taken up an electron from another atom thereby forming a negative ion. That’s the -ide in sodium chloride, which is common table salt. Lanthanoids are lanthanoids no matter what element they are or are not bonded to.
And the periodic table being periodic, the story repeats itself with the actinoids. If you listened carefully tonight you knew Amy already ruled those out, because they are all radioactive.