Ionization Energy
Ionization energy (IE) is the energy required to remove an electron from a neutral atom or cation in its gaseous phase. IE is also known as ionization potential.
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Conceptually, ionization energy is the affinity of an element for its outermost electron (an electron it already has in its valence shell).
1st, 2nd, and 3rd Ionization Energies
The symbol \(I_1\) stands for the first ionization energy (energy required to take away an electron from a neutral atom, where \(n=0\)). The symbol \(I_2\) stands for the second ionization energy (energy required to take away an electron from an atom with a +1 charge, \(n=2\).)
First Ionization Energy, \(I_1\) (general element, A): \( A_{(g)} \rightarrow A^{1+}_{(g)} + e^- \)
Second Ionization Energy, \(I_2\) (general element, A): \( A^{1+}_{(g)} \rightarrow A^{2+}_{(g)} + e^- \)
Third Ionization Energy, \(I_3\) (general element, A): \( A^{2+}_{(g)} \rightarrow A^{3+}_{(g)} + e^- \)
Each succeeding ionization energy is larger than the preceding energy. This means that \(I_1
General periodic trends in electron affinity
In general, ionization energies increase from left to right and decrease down a group; however there are variations in these trends that would be expected from the effects of penetration and shielding. The trends in first ionization energy are shown in Figure \(\PageIndex{1}\) and are summarized below.
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