Revising the Periodic Table Based on Different Pressures

​The periodic table has been an important foundational tool for material research since it was first put together 150 years ago. Currently, Martin Rahm from Chalmers University of Technology presents a new article which adds a totally new dimension to the table, delivering a new set of principles for material research. The article has been published in the Journal of the American Chemical Society.

Martin Rahm of Chalmers University of Technology presents a new study which maps how the properties of elements change under pressure. The research offers material researchers an entirely new set of tools to work with. (Illustration: Yen Strandqvist/Chalmers)

The research maps how both the electronegativity and the electron configuration of elements vary under pressure. These findings provide materials scientists a completely new set of tools. Largely, it means it is currently plausible to make rapid predictions about how some elements will act at different pressures, without necessitating experimental testing or computationally expensive quantum mechanical calculations.

Currently, searching for those interesting compounds which appear at high pressure requires a large investment of time and resources, both computationally and experimentally. As a consequence, only a tiny fraction of all possible compounds has been investigated. The work we are presenting can act as a guide to help explain what to look for and which compounds to expect when materials are placed under high pressure.

Martin Rahm, Study Lead and Assistant Professor in Chemistry, Chalmers University of Technology

At high pressures, the properties of atoms can vary drastically. The new research demonstrates how the electron configuration and electronegativity of atoms alter as pressure rises. Electron configuration is important to the structure of the periodic table. It establishes which group in the system different elements fit into.

Electronegativity is also a fundamental concept in chemistry and can be seen as a third dimension of the periodic table. It specifies how powerfully various atoms attract electrons. Together, electronegativity and electron configuration are essential to understand how atoms react with each other to develop different substances.

At high pressure, atoms which usually do not combine can form new, never before seen compounds with exclusive properties. Such materials can stimulate scientists to try other techniques for creating them under more regular conditions, and offer us new understanding into how the world functions.

At high pressure, extremely fascinating chemical structures with unusual qualities can arise, and reactions that are impossible under normal conditions can occur. A lot of what we as chemists know about elements’ properties under ambient conditions simply doesn’t hold true any longer. You can basically take a lot of your chemistry education and throw it out the window! In the dimension of pressure there is an unbelievable number of new combinations of atoms to investigate.

Martin Rahm, Study Lead and Assistant Professor in Chemistry, Chalmers University of Technology

A familiar example of what can take place at high pressure is how diamonds can be developed from graphite. Another instance is polymerization of nitrogen gas, where nitrogen atoms are pushed together to bond in a 3D network. These two high-pressure materials are very dissimilar to each other. While carbon retains its diamond structure, polymerized nitrogen is unbalanced and returns back to gas form when the pressure is discharged.

If the polymer structure of nitrogen could be preserved at regular pressures, it would indisputably be the most energy dense chemical compound on Earth.

Presently, a number of research teams use high pressures to develop superconductors—materials which can conduct electricity without resistance. A few of these high-pressure superconductors work close to room temperature. If such a material could be enabled to function at standard pressure, it would be ground-breaking, facilitating, for instance, lossless power transfer and inexpensive magnetic levitation.

“First and foremost, our study offers exciting possibilities for suggesting new experiments that can improve our understanding of the elements. Even if many materials resulting from such experiments prove unstable at normal pressure, they can give us insights into which properties and phenomena are possible. The steps thereafter will be to find other ways to reach the same results,” says Martin Rahm.

High Pressure Research

The study has theoretically projected how the nature of 93 of the 118 elements of the periodic table varies as pressure increases from 0 pascal up to 300 gigapascals (GPa). 1 GPa is about 10,000 times the pressure of the Earth’s surface. 360 GPa matches the very high pressure found close to the Earth’s core. Technology to refabricate this pressure exists in some laboratories, for example, using shock experiments or diamond anvil cells.

The pressure that we are used to on Earth's surface is actually rather uncommon, seen from a larger perspective. In addition to facilitating for high pressure material synthesis on Earth, our work can also enable a better understanding of processes occurring on other planets and moons.

Martin Rahm, Study Lead and Assistant Professor in Chemistry, Chalmers University of Technology

He added, “For example, in the largest sea in the solar system, many miles under the surface of Jupiter's moon Ganymede. Or inside the giant planets, where the pressure is enormous.”

The study was carried out using a mathematical model, wherein each atom was positioned in the middle of a spherical cavity. The effect of augmented pressure was replicated via a steady reduction of the sphere’s volume. The physical properties of the atoms in various stages of compression could then be measured using quantum mechanics.


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