Ionization energy is a measure of how strongly an atom holds onto its electrons. a higher ionization energy indicates that more energy would be needed to remove an electron. atoms that have a smaller atomic radius tend to have higher ionization energies because their electrons are closer to the nucleus. based on the periodic table, which element would be expected to have the lowest ionization energy? a) calcium (ca) b) cesium (cs) c) sodium (na) d) strontium (sr) wrong answers will be reported.