Thursday, March 27, 2014

Discovery of Oxygen

This tweet has been making the rounds today. It shows each element by its nation(s) of initial discovery, except of course elements like iron which date to antiquity. Europe claims most of the 18th and 19th century elements, while the U.S. seems to dominate in the modern ones, i.e. astatine plus the transuranium elements.

Overall I think it's a fascinating chart, but I do have a couple of problems with it. One, it lists element 117 as undiscovered, despite the fact that it was synthesized by a joint U.S.-Russian team in 2010. Still, element 117 hasn't been officially accepted by the IUPAC/IUPAP, so I suppose the creators are just playing it safe.

But more importantly, I feel the chart's creators err when they assign the discovery of oxygen to England and Sweden. For the historical record, Carl Wilhelm Scheele of Sweden in 1772 and Joseph Priestley of England in 1774 both independently isolated oxygen by heating HgO and the like. Although Scheele performed his experiment first, Priestley published first, so there's some question as to which one deserves more credit-this chart seems to split the difference.

Monday, March 24, 2014

Surprising Article about Californium Chemistry

I just saw an interesting article from the RSC at Chemistry World based on this article in Nature Chemistry about the chemistry of californium. Researchers at Florida State University were supplied by the U.S. Department of Energy with several milligrams of 249Cf which was reported as being worth over a million dollars(!). They proceeded to synthesize a californium borate compound and they report on their experimental findings and electronic structure explanations of said findings.

The authors claim that "...there are, in fact, few parallels between lanthanide and actinide chemistry." The article continues that actinide chemistry (or californium-highly polarizable ligand chemistry, at any rate) in many respects is actually more similar to d-block behavior than expected f-block behavior.

What was particularly interesting was that the f-orbitals where also involved in bonding. The original article in Nature Chemistry discusses some DFT calculations on the californium borate, using a "60-electron core quasi-relativistic pseudopotential" for the californium. As far as I can tell, the authors where primarily concerned with scalar relativistic effects (i.e. s- and p-shell contraction and d- and f-shell expansion) rather than spin-orbit coupling. If so, the explanation for their results should be that the higher degree of s-orbital contraction in the actinides versus the lanthanides results in substantially larger f-orbitals, which are better able to form covalent bonds.

In any event, this article opens some interesting questions about heavy element chemistry, and I'm excited to seeing where it will lead.

Sunday, March 9, 2014

Astatine: Halogen or Metal? Part 3: Electronic Structure Calculations

For "Part 1: Background" click here. For "Part 2: Introduction to Relativistic Quantum Chemistry" click here.

In this post I will be applying the lessons of Part 2 on relativistic quantum chemistry to discuss papers which publish significant (relativistic) electronic structure calculations of astatine. To date, I have only found two which I would put in this category; they are referenced at the end of the paper. Articles of lesser direct significance will be referenced as they come up. I will attempt to keep this blog post updated as I become aware of other articles or as they are published. If anyone is aware of any relevant articles, I would greatly appreciate if you leave a reference or link in the comments below.