2.3.1: Ionization Energy

• Ionization energy is the energy required to remove an electron from a neutral atom or cation in its gaseous phase.
• First ionization energy is the energy required to take away an electron from a neutral atom.
• Second ionization energy is the energy required to take away an electron from an atom with a +1 charge.
• Each succeeding ionization energy is larger than the preceding energy.
• Ionization energy is correlated with the strength of attraction between the positively-charged nucleus and the negatively-charged valence electrons.
• Ionization energies increase from left to right and decrease down a group.
• As Z* increases across a period, the ionization energy generally increases from left to right.
• Ionization energy is especially low when removal of an electron creates a newly empty p subshell or a half-filled p or d subshell.
• Ionization energy increases more gradually across the d- and f-subshells because d- and f- electrons are weakly penetrating and experience especially low Z*.
• There is a large decrease in ionization energy with the start of every new period.
• The noble gases posses very high ionization energies, while Helium has the highest ionization energy of all the elements.