The six-bond bound

摘要

What is the maximum number of covalent chemical bonds that two atoms can share? Six, according to the latest theoretical study — at least where just two atoms of the same element are concerned. Every atom can make a small, integer number of covalent chemical bonds with neighbouring atoms. This number is usually not more than eight, although a precise statement is dangerous — in rare cases, atoms can have more than eight neighbours, but whether they are covalently bound is open to debate. By the nineteenth century, chemists had realized that more than one bond may connect the same two atoms: most famously, adjacent carbon atoms can be bound twice or even three times.