<Dd> Z (\ displaystyle Z \!) is the atomic number, i.e. the number of protons in the atomic nucleus of this element; </Dd> <Dd> n 1 (\ displaystyle n_ (1) \!) and n 2 (\ displaystyle n_ (2) \!) are integers such that n 1 <n 2 (\ displaystyle n_ (1) <n_ (2) \!), corresponding to the principal quantum numbers of the orbitals occupied before and after . </Dd> <P> It's important to notice that this formula can be directly applied only to hydrogen - like, also called hydrogenic atoms of chemical elements, i.e. atoms with only one electron being affected by an effective nuclear charge (which is easily estimated). Examples would include He, Li, Be etc., where no other electrons exist in the atom . </P> <P> But the Rydberg formula also provides correct wavelengths for distant electrons, where the effective nuclear charge can be estimated as the same as that for hydrogen, since all but one of the nuclear charges have been screened by other electrons, and the core of the atom has an effective positive charge of + 1 . </P>

Why does the rydberg equation work for hydrogen and not helium
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