Material properties change at high pressure. Scientists can generate pressures millions of times above ambient pressure and, in doing so, have found near-room-temperature superconductors, polymeric nitrogen, and other surprises. To better understand how elements behave under pressure, Martin Rahm of Chalmers University of Technology and colleagues predicted the electronegativity and electron configuration of individual atoms of elements 1 through 96—except for thorium, uranium, and neptunium, which they could not calculate—in a nonreactive environment up to 300 GPa (J. Am. Chem. Soc. 2019, DOI: 10.1021/jacs.9b02634).
Rahm says some of a chemist’s intuition about periodic trends breaks down for high-pressure systems, and he wanted to provide a guide to this regime. The researchers confirmed that under pressure, electronic orbitals generally fill according to the principal quantum number. In potassium, for instance, the 3d orbital fills before the 4s at 300 GPa, the opposite of what happens at ambient pressure. They calculated that trends of electronegativity are less predictable at high pressure for elements in groups 1–10, the lanthanides and actinides. Rahm says the results could help predict changes in polarity or reactivity at high pressure.