Electrons are attracted to the nucleus due to their opposite charge. This means that energy must be supplied to pull an electron away from the nucleus , thus leaving a positively charged species and free electron . The ionazation energy is the minimum energy required to remove an electron from an atom.
• Having understood the above, when electrons are at various distance , the force on them are different, so is the ionazation energy.
• The further the electron from the nucles, the weaker nuclear attraction , the less ionazation energy.