Friday, June 10, 2016

TETRIS! Seventh Row of Periodic Table Completed

What do the nation of Japan, the state of Tennessee, and the city of Moscow have in common with Russian nuclear physicist Yuri Oganessian? If you hadn't guessed, all four just had elements named after them, marking the observation and naming of all elements in the seventh row of the periodic table.

The periodic table of elements, complete with its latest additions.
If the universe is a game of Tetris, we definitely just beat a level.
Nihonium, moscovium, tennessine, and oganesson are the latest additions to the chart, assigned to elements with atomic number 113, 115, 117, and 118 respectively. Atomic number refers to the number of protons in each atom's nucleus, and correspondingly to the number of electrons that orbit the protons and neutrons. It is the number of electrons that primarily determines an element's physical properties.

Element 113, nihonium, was named after the nation of Japan—Nihon means "Land of the Rising Sun" in Japanese. Nihonium was synthesized in Japan, by bombarding a block of bismuth with a ions of a heavy zinc isotope (zinc-70) at extremely high speeds. Researchers didn't identify the new element directly, but rather its decay products—nihonium is highly unstable, so right now the only way to figure out that you had some is to look at the pieces it breaks into.

Moscovium takes its name from the Russian capital city of Moscow, where the element was produced using a similar process to nihonium, except using americium (popular ingredient of smoke detectors) as the target and ions of calcium as the "bullet". The research took place at the Joint Institute for Nuclear Research (JINR), which is a collaboration among 1200 scientists from 18 different countries.

Tennessee earned itself a spot on the list by being home to Oak Ridge National Laboratory (ORNL) as well as Vanderbilt University and the University of Tennessee. Although tennessine was also produced at the JINR near Moscow, it couldn't have been done without some help from the people at ORNL. Tennessine was produced using the same calcium-48 beamline that produced moscovium, but with a target made of the manmade element berkelium. Berkelium itself is produced by bombarding plutonium (#94 on the periodic table) with neutrons until it turns into curium (#96). If you're following closely, you might be scratching your head right now—isn't the atomic number supposed to depend on the number of protons in the nucleus? How does bombarding plutonium with neutrons turn it into curium?

It turns out that, at a subatomic level, the properties of matter aren't set in stone—as long as charge, mass, and energy are conserved, just about anything goes! Under the right circumstances, a neutron inside a nucleus will turn into a proton by spitting out an electron—a process called beta decay (more specifically, beta-minus decay, since it's giving off a negatively charged electron). You could think of the neutron as containing an electron and a proton that are very tightly bound and whose charges cancel one another out, but this isn't quite right—a proton can also turn into a neutron, by spitting out a an antimatter positron! This is known as beta-plus decay. So by lodging a bunch of extra neutrons in a plutonium nucleus and then allowing those neutrons to transform into protons through beta-minus decay, we can get elements like curium. Curium then quickly goes through another beta-minus decay reaction, to produce the far more stable berkelium. Once the scientists at ORNL obtained a sufficient amount of berkelium, they sent it to the JINR to be bombarded with calcium-48, resulting in tennessine.

The last element on the list, filling out the far bottom right corner of the table, is Oganesson. You'll notice that this one has a different naming convention than the rest—like all elements in the far right-hand-column of the table (besides helium), it ends in -on, in accordance with IUPAC's rules on the names. As mentioned above, Oganesson was named after Professor Yuri Oganessian, who largely spearheaded the JINR's efforts to synthesize and categorize the new superheavy elements.

These names aren't QUITE official yet, however—there's a public review period that goes until Novemer 8th, where anyone can submit comments, suggestions, or objections. There are at least 50,000 people out there set on seeing element 117 named Octarine, which could technically qualify as a mythological concept, since it's from Terry Pratchett's Discworld series, so now's the time to let the IUPAC know! Barring that, we can look forward to seeing the provisional version shown above become permanent.

I think humanity deserves a collective pat on the back for this one. We did it! There's always more to be done, new electron shells to explore, new islands of stability to try and reach, but for now it feels like having a full pokédex, like clearing a row in a game of Tetris. Go science!

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