Which of the following elements would you expect to have the lowest ionization energy value, and why?

Fluorine (F), because it is a halogen that naturally forms a negative ion

Lithium (Li), because it has a low effective nuclear charge and large radius

Neon (Ne), because it is a noble gas with a full energy level and small radius

Nitrogen (N), because it is a nonmetal that does not have a full outer energy level

The element with low ionization value is "Lithium (Li), because it has a low effective nuclear charge and a large radius." Ionization energy is defined as energy that an isolated gaseous atom needs to absorb to free an electron. The elements, Lithium (Li), Fluorine (F), Nitrogen (N), and Neon (Ne) are in period 3 of the periodic table. When you move across a period from left to right the number of protons increase which in turn leads to an increase in effective nuclear charge. In addition, the atomic radius decreases because of the increase in nuclear charge. This leads to electrons being held more tightly by the nucleus, hence more ionization energy is required to remove the valence electrons.