Periodic Trends - Example

Cl, Al, Cs, Na

First ionization energy is directly related to the ofrce of attraction between the electrons in the valence energy level and the nucleus
The stronger the force of attraction the greater the energy required to remove a valence electron, with force of attraction being dirctly proportional to the ENC and indirectly proportional to the distance to the valence energy level.

Cs will have the lowest force attraction, and therefor lowest first ionization energy, as it has the greatest distance to the valence energy level.

Na, Al, and Cl are all in the same period, resulting in them having the same general distance to the valence energy level and therefore any differences in their first ionization energy would mainly be due to their ENCE values.

• Na, being in group 1, has the lowest ENC (value = 1) and therefore of the three elements in the same period it will have the lowest F_attract and will have the low first ionization energy of the three (Na, Cl, Al)
• Al has the second lowest ENC value (value = 3) of the three elements in the same period, and therefore since its ENC is greater than that of Na, it will have a stronger F_attract than Na, and will therefore will require a greater amount of energy to remove an electron giving it a larger first ionization energy
• Cl has the highest ENC (value = 7) of the three elements in the same period and therefore it will have the greatest F_attract requiring the most energy to remove an electron, resulting in Cl having the greatest first ionization

Cs < Na < Al < Cl