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Ionization Energy is the energy required to remove the most loosely held electronfrom the outer energy level of an atom in the gas phase. The first ionization energy is the energy required to remove the first electon from an atom, the second ionization energy is the energy required to remove a second electron, and so on.
- A general equation for the removal of an electron:M(g) + energy --> M+(g) + e-
- Ionization Energy is a periodic property, as illustrated in the graph below
- In general, as the atomic number increases in a period, the ionization energy increases. This is because there is an extra proton that increases the coulombic force, thus increasing the amount of energy needed to remove that valence electron.
- However, as one moves down a group, the ionization energy decreases. This is due to the fact that each successive element in a group has another energy level. The increased distance from the nucleus decreases the coulombic attraction.
- Also, since there are more energy levels of electons below the outer shell, a shielding effect occurs. In this shielding effect, there is a repulsion between the inner and valence electrons.
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