Wednesday, October 16, 2019

Element of the Month: Selenium!

October's Element of the Month:


Atomic Mass: 78.971 amu
Melting Point: 221 °C
Boiling Point: 685 °C

You may remember that a few Elements back, when we were chatting about Tin, the idea of "allotropes" came up. We talk about allotropes when an element can take more than one form without changing state -- if it has two different forms it can take that are both solids, for example. Tin, for instance, can be a bright, shiny, useful, malleable metal, or -- if you get it too cold, for instance -- can be a dull, grey, hateful, useless powder.

Selenium, October 2019's Element of the Month, is all about the allotropes. If you isolate it through a chemical reaction and just dry it out or whatever, you get kind of a red powder. It's not a silvery-grey metal! But then, Selenium is not a metal. It is, in fact, what chemists call a "non-metal." It's like Sulfur, for instance. Indeed, Selenium is right under Sulfur in the periodic table, and they hang out together a lot in the mineralogical sense, so it's not surprising that it forms a similar sort of powder, except that it's a sober brick-red instead of Sulfur's irrepressibly cheerful yellow.

But let's say you melt elemental Selenium quickly. Whoa! It morphs into "beads," which are these little semigloss black pellets shaped like oversized red blood cells. Or, if you put it into a solution and evaporate out the solution, you can get one of three kinds of bright red crystals. If you heat it up slowly, it might morph into a dull grey allotrope.

The Centerfold!

Selenium was discovered by Jöns Jakob Berzelius, last seen in these pages discovering Thorium, and Johan Gottlieb Gahn, who was last seen letting his friends Torbern Bergman and Carl Wilhelm Scheele get all the credit for his discovery of Manganese. Gahn was a young fellow of 29 when he came up with Manganese, but by the time he and Berzelius found a reddish impurity in their sulfuric acid factory he was 72 years old. You might think a man of his years would be thinking in terms of a legacy in the annals of chemistry, but no -- once again he punted on the publishing and let Berzelius handle the write-up. He just didn't like publishing.  That's why Berzelius, like Bergman and especially Scheele, remains a well known figure in the history of science today.  All Johan Gottlieb Gahn ever did is foster the industrial revolution in Sweden and make massive bank.

Updated Score:
Carl Wilhelm Scheele - 26.9K Wiki Article
Jöns Jacob Berzelius - 21.1K Wiki Article
Torbern Bergman - 7.5K Wiki Article
Johan Gottlieb Gahn - 3.5K Wiki Article

The grey allotrope of Selenium is a semiconductor, meaning it has a moderate conductivity to electricity that can be controlled in various useful ways. It is also photoconductive, which means it becomes more conductive to electricity in brighter light. Which frankly sounds crazy, but apparently it's true. In fact, it's not even unique, which is why Selenium isn't in nearly as much demand in today's electronics industry as it used to be. Other semiconductors and photoconductors are cheaper and more efficient. That leaves Selenium with various niche applications, but you know what we do with half of the volume we produce of it? We put it in commercial glass, which stains it just a little bit red. That sounds like a terrible idea, except for that there are iron impurities in glass-making silicon that tend to make it just a little bit blue-green. Getting the red in there evens out the tone to what we read as a nice, neutral clear.

You need a little bit of Selenium for your enzymes and what-not to function properly, but you are getting enough. Don't go out of your way to get more, or you'll give yourself selenosis, which would be a real drag.

Selenium, an art print by Spanish illustrator Alvaro Cubero, who
sells his work here.

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