atomic number
Electron configuration notation eliminates the boxes and arrows of orbital filling diagrams. Each occupied sublevel designation is written followed by a superscript that is the number of electrons in that sublevel. For example, the hydrogen configuration is 1 s 1 , while the helium configuration is 1 s 2 . Multiple occupied sublevels are written one after another. The electron configuration of lithium is 1 s 2 2 s 1 . The sum of the superscripts in an electron configuration is equal to the number of electrons in that atom, which is in turn equal to its atomic number.