Bond order through a molecular orbital lens

Although bond order is a well-established concept, it has proven hard to define in a way that balances chemical sense and physical rigor. Even simple diatomic molecules can be tricky: chemists have debated whether the attraction in C₂ could be called a quadruple bond, for example. To help understand these problems, researchers in the US have introduced a new tool that describes chemical bond orders in terms of contributions from molecular orbitals, as part of a survey of almost 300 diatomic molecules across the periodic table.