Carbon–bismuth bonds reveal that relativity blurs the textbook line between sigma and pi bonds

Brown University chemists have provided direct evidence that upends the textbook explanation of how triple chemical bonds work in heavy elements. In a study published in Science, the researchers show evidence that when atomic nuclei are sufficiently heavy, the principles described in Einstein's theory of relativity change the structure of triple bonds—blurring the lines between the two separate types of bonds involved in textbook triple bonding.