Electron orbitals show where and how electrons move around atomic nuclei and molecules. In modern chemistry and physics, they have proven to be a useful model for quantum mechanical description and prediction of chemical reactions. Only if the orbitals match in space and energy can they be combined -- this is what happens when two substances react with each other chemically. In addition, there is another condition that must be met, as researchers have now discovered: The course of chemical reactions appears to be also dependent on the orbital distribution in momentum space.
