Superheavy elements are the least co-operative substances in chemistry. They are made by slamming beams of ions into targets in accelerators, emerge at rates of a few atoms per hour or per day, and decay in seconds to minutes — sometimes less. You cannot weigh them, dissolve them, or put them in a beaker.
What you can do is run gas-phase chemistry. An atom is transported in a gas stream, allowed to react with a carefully chosen molecule for a fraction of a second, and the resulting compound is identified by its volatility and adsorption behaviour rather than by spectroscopy. Golem reports that researchers have used this approach to bind a superheavy transuranium element with carbon monoxide — the same ligand that forms metal carbonyls from nickel to iron.
Carbon monoxide is a useful probe precisely because it is chemically simple and electronically demanding. It donates electron density into a metal's d orbitals and accepts it back into its own empty π* orbitals, and the strength of that back-donation depends finely on the metal's energy levels. For very heavy nuclei, those levels are shifted by relativistic effects: electrons in inner shells move fast enough that their mass increases measurably, contracting s and p orbitals and reshuffling the ordering of the d and f states. Carbonyl formation is therefore a direct experimental test of whether the periodic table behaves the way relativistic calculations say it should at its far edge.
The details — the specific element and the laboratory — are reported by Golem; the significance is broader than one compound. Each such experiment is a data point on the question of where the periodic table stops behaving periodically, and it is a test that no theory can perform on its own — because the only instrument that can run it is an accelerator, an atom stream, and a molecule that is willing to bond to something that will not survive the second.
