New Insights Challenge Classic Core Electron Bonding
In a surprising turn that could rewrite a chapter of chemistry, researchers at the University at Buffalo have suggested that core electrons may participate in chemical bonding under far gentler conditions than previously believed. The team’s quantum chemical calculations, published in the Journal of the American Chemical Society, focus on semicore electrons in alkali metals—the highly reactive elements at the left edge of the periodic table. Their results imply that core-electron involvement in bonding can occur at pressures only a few gigapascals, levels found in the Earth’s deep crust and upper mantle, but far below the hundreds of gigapascals once considered necessary.
Perhaps most striking is the finding that in cesium, semicore electrons could participate in bonding even at ambient pressure. This challenges longstanding assumptions about the isolation of inner-shell electrons from bonding interactions and signals a broader role for core-like electrons in real-world chemistry.
How Semicore Electrons Contribute at Low Pressures
The UB study centers on the B1–B2 transition—a structural rearrangement in certain compounds driven by pressure. In typical alkali metal fluorides, the structure exists in a more octahedral (B1) arrangement at low pressures, whereas a cubic (B2) form emerges under higher pressure. The researchers show that semicore electrons don’t merely “watch” bonding from the inside; they actively participate, helping to drive and stabilize the B2 cubic structure as pressure rises. Using state-of-the-art quantum chemistry models run on UB’s Center for Computational Research, the team demonstrates that even modest pressures can unlock this inner-shell participation.
“Our results indicate that semicore electrons are a more lenient partner in bonding than we once thought,” notes Eva Zurek, PhD, SUNY Distinguished Professor of Chemistry and co-corresponding author. “This challenges traditional notions of core electrons and opens new avenues for understanding how materials behave under pressure, not just in laboratories but in planetary interiors.”
Implications for Planetary Science and Materials
The insights extend beyond academic curiosity. If semicore bonding alters how elements bond under pressures akin to Earth’s crust and mantle, researchers must reconsider models of planetary structure, evolution, and magnetic field generation. Changes in bonding could influence mineral densities, phase transitions, and even the interpretation of seismic data used to probe planetary interiors. In short, a subtle shift at the electron level could ripple through geophysics and planetary science, affecting calculations of a planet’s radius, tectonic behavior, and habitability.
The findings also offer a roadmap for experimental validation. The UB team suggests targeted experiments, including X-ray diffraction studies, to characterize the atomic arrangements of alkali metals under pressure and to test the role of semicore electrons in bonding under conditions accessible in today’s high-pressure facilities.
Looking Ahead: What Comes Next
While the work is theoretical, its potential impact is tangible. By expanding the framework of how core-like electrons participate in bonding, scientists can refine models of matter under extreme conditions—conditions that exist not only in the lab but across Earth-like planets and their atmospheres. As Zurek and her colleagues emphasize, the next steps involve collaboration with experimentalists to confirm or refine the predicted behavior and to explore the practical implications for materials science and planetary formation theories.
Conclusion
The idea that core electrons might engage in bonding at low pressures reframes a long-standing tenet of chemistry. For alkali metals, semicore electrons could be active players even at ambient conditions, shaping the structural transitions that govern material properties. As researchers pursue experimental validation, the scientific community will gain a clearer picture of how elements bond under pressure—and what that means for our understanding of planets and their evolution.
