For complex atoms we have to use a new
and radical theory based on Quantum Mechanics, which provides a more
complete picture of the atomic structure *
Hydrogenic atoms are the atoms consisting of a nucleus with positive charge
+Ze and a single electron, where Z is the proton number Examples are hydrogen
atom, singly ionised helium, doubly ionised lithium, and so forth In these
atoms more complex electron-electron interactions are nonexistent