Wednesday, March 20, 2019

Element of the Month: Rubidium!

March's Element of the Month:


Atomic Mass: 85.468 amu
Melting Point: 39.30 °C
Boiling Point: 688 °C

Rubidium is about the 23rd most common element in the Earth's crust, not really common enough to be vital and interesting but not quite rare enough to be exotic and interesting either. It sits way over on the leftmost column of the table of the elements and shares characteristics with its upstairs neighbors Sodium and Potassium.  Both those guys are big players in the web of life, while Rubidium is completely irrelevant to any living being. It's so innocuous that even when it occasionally gets taken up into your biochemistry where Potassium should have been, it doesn't even cause problems. It just, I don't know, finds its way back out of your system in the next chemical reaction.

In its pure state, which is to say in the lab, Rubidium is a soft silvery metal with a melting point of 39.3 °C, ​which is to say 102.7 °F, which is to say it melts in your hand if you're running a fever, or climb a long staircase, or live in Phoenix. This makes it one of the metallic elements less suited for high performance engine parts and applications in the aerospace industry.

It doesn't occur in nature in its pure state; like Sodium and Possassium, it oxidizes quickly in air and bursts into violent flame when exposed to water. Well, what actually happens is that your "alkali metal" of choice reacts very vigorously with the oxygen in the water, an exothermic reaction that creates a lot of heat right next to where a whole lot of hydrogen atoms are being orphaned. So, it's the hydrogen that does a lot of the burning. In any event, don't try it, or if you do try it, start small, and in a outdoor location relatively free of children, animals, and law enforcement officers.

The Centerfold!

If you're thinking that it would be more fun to pour the
Rubidium out of the tube directly into your hand, you
lose three points for Slytherin.  Go back and read the
text again until you understand why that's not a good idea.

"Rubidium" means "deep red," which Rubidium is not. The name comes from flame spectroscopy. You may know about spectroscopy. That's the thing where, when you superheat atoms, they emit a pattern of light waves. Conveniently enough, each element has its own distinctive spectral fingerprint, and when Robert Bunsen and Gustav Kirchhoff discovered Rubidium through flame spectroscopy in 1861, they named it after the deep red lines that are its signature. Or so the story goes. Only problem is, when you look at the spectral signatures of all the elements, Rubidium's is not particularly heavy in the reds. But, whatever.

How did Bunsen and Kirchhoff superheat their Rubidium to perform flame spectroscopy? With a Bunsen burner, of course! Bunsen invented it, with the help of a research assistant, and he used it with Kirchhoff to discover not only Rubidium but also Caesium which, I hate to harp on this, seems to have a hell of a lot more red in its spectroscopic signature than Rubidium does. Did Caesium and Rubidium get switched in the nursery, or something?  Am I really the first person to notice this?

Anyway, Robert Bunsen got the immortality of the Bunsen burner, but how sad, Gustav Kirchhoff was doomed to obscurity? Not so fast, you. You're forgetting Kirchhoff's circuit laws of electrical engineering, Kirchhoff's three laws of spectroscopy, Kirchhoff's law of thermochemistry, Kirchhoff's law of thermal radiation, and the Kirchhoff equations in fluid dynamics. He was, like, super smart, OK? In fact, it's probably time you accepted that you're just not going to make as much of a splash in the history of science as Gustav Kirchhoff did. And that's all right. You're still a good person. Not everyone can be Gustav Kirchhoff.

Cover for the album Rubidium, by Finnish jazzcats Black Motor.  They're pretty good.

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