At the bottom right-hand corner of the periodic table sits a fantasy world. Until recently, these elusive elements’ names were just fancy translations of their numbers. They’re enormous and can only be produced in the lab. They only stick around for a few seconds at most before radioactively decaying into smaller elements.
And when researchers from Michigan State University, as well as New Zealand and Norway, tried to deduce the properties of the heaviest element, oganesson, it was every bit as weird as you might imagine.
Through their calculations published in Physical Review Letters, they show that “[oganesson] is a rather unusual addition to the periodic table.” In fact, the element is could be missing an electron shell structure entirely.
Quick chemistry lesson: there are 118 elements on the periodic table. Normally, the atoms of each comprise of a proton and a neutron in a core called the nucleus. The number of protons determines the element’s identity. Each then has some number of electrons surrounding the nucleus.
The rules of quantum mechanics say that these electrons don’t really orbit, but instead are most likely to appear in special regions. Each region gets a number, the “energy level,” and a letter, its shape. The electrons fill these regions in a special order. The first two appear in a region called “1s,” which is sphere shaped. The next are in 2s, also sphere shaped. Then there’s 2p (three dumbbells at right angles), which holds six electrons. That goes on to include d and f orbital shapes, which hold 10 and 14 electrons, respectively.
Oganesson, if it followed the rules, would have its electrons organised in (take a deep breath) 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, and 7p. The completed 7p shell means that it should be a “noble gas,” potentially with properties similar to xenon or neon.
But heavy elements don’t follow the rules. Bigger atoms’ outermost electrons must travel fast enough to not fall into the nucleus, writes Angela Wilson, a Michigan State chemist not involved in the research, for Physics. This means a different set of physical laws, the laws of special relativity, come into play. Gold’s colour and mercury’s low melting points come from these relativistic expects, she wrote.
And oganesson should be equally weird. The physicists tried to predict its properties based on calculations of its electrons’ behaviour. It turns out that they should act as a special kind of electron gas, or Thomas Fermi gas, around the nucleus. These huge atoms might no longer have those well-defined energy levels. It’s not like xenon or neon at all.
Basically, Oganesson is so big that it would completely throw the high school rules of how electrons organise themselves around atoms out the window.
While still just theory, these results are important, wrote Wilson: “These important insights about the electronic and nucleonic shell structure of oganesson open the door to further theoretical investigation into its unusual properties. The remarkable results may also provide encouragement to experimentalists to develop instruments and experiments to enable further studies of the chemical and physical properties of superheavy elements.”