Breaking The Rules...

UNUSUAL BONDS: Chemical bonds between cesium (Cs) and fluorine (F) might form with not just valence electrons, but inner-shell electrons as well under very high pressures, new calculations suggest.
Image: Maosheng Miao

A study suggests atoms can bond not only with electrons in their outer shells, but also via those in their supposedly sacrosanct inner shells

By Clara Moskowitz

Most of us learned in high school chemistry class that chemical bonds can only form when electrons are shared or given away from one atom’s outer shell to another’s. But this may not be strictly true. A chemist has calculated that under very high pressure not just the outer electrons but the inner ones, too, could form bonds.

Inside atoms, electrons are organized into energy levels, called shells, which can be thought of as buckets of increasing size that can each hold only a fixed number of electrons. Atoms prefer to have filled buckets, so if their outer shell is missing just one or two electrons, they are eager borrow form another atom that might have one or two to spare. But sometimes, a new study suggests, atoms can be incited to share not just their outer valence electrons, but those from their full inner shells. “It breaks our doctrine that the inner-shell electrons never react, never enter the chemistry domain,” says Mao-sheng Miao, a chemist at the University of California, Santa Barbara, and the Beijing Computational Science Research Center in China. Miao predicted such bonds using so-called first-principles calculations, which rely purely on the known laws of physics, and reported his findings in a paper published September 23 in Nature Chemistry. Such bonding has yet to be demonstrated in a lab. Nevertheless, “I’m very confident that this is real,” he says. (Scientific American is part of Nature Publishing Group.)

Scientific American: A Basic Rule of Chemistry Can Be Broken