I order for an atom to lose an electron, the attraction between the electron and the protons has to be broken. When an atoms don't have a outer orbital of electrons they will have a negative or a positive charge. For them to become neatural they will gain or lose electrons.
Electrons are attractive towrads nucleus due to electromagnetic forces between +ve & -ve charges. We must supply those minimum energy (ionization energy) which can break that bond, then atom will lose an electron
