Brown University chemists have reported experimental evidence that relativistic effects alter the structure of triple chemical bonds in heavy elements, as detailed in a Science paper published July 9, 2026. In classical chemistry, a triple bond comprises one sigma bond and two pi bonds, with the sigma bond formed by head‑on orbital overlap and the pi bonds by side‑by‑side overlap. At the bottom of the periodic table, heavy nuclei increase electron velocities to a significant fraction of light speed, invoking Einstein’s theory of relativity. The Brown team created molecules combining carbon with bismuth, a heavy element adjacent to lead, and cooled them to near absolute zero before analyzing them with photoelectron spectroscopy, which measures electron ejection distances to infer bond strength. The resulting spectrum indicated that the carbon‑bismuth bonds did not conform to the textbook sigma‑pi model; instead they displayed one pi bond and two hybrid sigma‑pi bonds. ‘The boundary between a sigma bond and a pi bond is now sort of smeared,’ said Lai‑Sheng Wang, a chemistry professor at Brown and corresponding author of the study. ‘We still have three bonds, but we do not strictly have a sigma or a pi.’ The findings suggest that chemistry textbooks may need revision as research on heavy elements expands, particularly for applications such as non‑toxic alternatives to lead in solar cells and for quantum materials. Funding for the work was provided by the U.S. National Science Foundation (CHE‑2403841) and the U.S. Department of Energy (DE‑SC0008501). Further studies are expected to assess the prevalence of relativistic bonding across other heavy elements.