Which of the following elements has the highest ionization energy? a. Ba b. Ca c. Cl d. Ne

Answer 1

Ionization energy is the energy that is required to dispel an electron from an atom. The farther away the electron is from the nucleus, the easier it is to ionize. This is why, as you go down the periodic table, the ionization energy decreases; the electron needs less energy to be discharged because the atomic radii increases and it is farther away from the nucleus.

However, as you go from left to right on the periodic table, the ionization energy increases because you are increasing the number of electrons in the outer shell. These electrons help to "shield" the other electrons and make it more difficult to dispel an electron. Therefore, of the options you have given, Neon would be the most difficult to ionize because it has a full octet of electrons. Since it would be the most difficult, Neon has the highest ionization energy.