Monday, April 8, 2013

Element of the Month: Europium!

April's Element of the Month:


Atomic Mass: 151.964 amu
Melting Point: 826 °C
Boiling Point: 1529 °C

Europium is a member of the “lanthanide series” of elements, which chemists define as “the ones between 57 and 71 that are really obscure and hard to remember when you take an elements quiz.” It is also one of the “rare earth” elements, which chemists think is a lame term but grudgingly define as “the lanthanides plus Cerium and Yttrium.” Rare earths aren’t EXCEEDINGLY rare in terms of their total volume here on the Earth’s crust – more in the Nickel/Tungsten/Uranium range than the Tellurium/Osmium/Gold range, if you follow me – but they are sneaky, elusive, and hard to find.

Why are they hard to find? Because they are so darn reactive. It is written that a cubic centimeter of Europium would completely oxidize in the open air within a few days. You don’t really need to run the numbers to realize that, at that rate, a vast mountain of Europium would oxidize and blow away on the winds within a human lifetime. It also dissolves easily and reacts in a friendly way with common elements like Calcium, so that even down there in the geology it never retains its elemental integrity. A “seam” of Europium? A “vein” of Europium? No such thing.

The Centerfold!

Europeum is a shiny silver metal in its elemental form, but you have
to work very hard to get it that way.
The lanthanides are all more or less chemically similar to each other due to the “lanthanide contraction.” I think. What’s the lanthanide contraction? Well, because these are pretty BIG atoms, their outer "shell" of electrons has a different relationship to the nucleus than do all of the closer-in shells. Most of the sources I’m looking at say that the radii of the lanthanide atoms get smaller more gradually than you’d expect them to as you go up through the series, although a few say that they get smaller more dramatically than you’d expect them to. I find this discrepancy unhelpful for the casual researcher. (Why does that outer electron shell get tighter as you move up through the series in the first place? I think it’s like this: because each additional electron adds an attractive charge to the shell, the shell as a whole is pulled closer in to the nucleus as the number of electrons within it increases.)

Anyway, being chemically similar, the lanthanides and their cousins in the rare earth category tend to end up in the same sorts of places. There are certain minerals that contain a couple percent of rare earth content, and these are mined with enthusiasm in China, California, and places like that. There’s no such thing as a “Europium mine,” though; rare earths are all mined in a batch and sorted out later. Depending on whom you ask, the lanthanide contraction is either what makes it DIFFICULT to sort them out one from another, or what makes it POSSIBLE to sort them out one from another. The internet sources really need to start singing from the same hymnal on this lanthanide contraction business.

Either way, it’s definitely tricky to separate them. The rare earths in general were more or less understood by about 1800, and after Mr. Mendeleev presented his famous spreadsheet in 1869 it must have been fairly clear that there were going to be a whole suite of similar elements in the lanthanide row.  Regardless, it wasn’t until 1901 that Eugène-Anatole Demarçay managed to isolate the impurity in his Samarium, which turned out to be elemental Europium. He named it, rather randomly it seems to me, after the continent of Europe.

“But what can I use Europium for?” you ask. So human a question. The main thing is, a few of its compounds glow in particular colors under certain stimuli. This makes it useful in certain data-display devices, quite possibly including the one you are currently staring into.

1 comment:

gl. said...

"The internet sources really need to start singing from the same hymnal on this lanthanide contraction business."

indeed. so much science, so little agreement.