Question

How would successive ionization energies of a given element evolve?

Answer 1

Successive ionizations require the expenditure of greater energy input, each time an electron is removed from the valence shell.

Explanation:

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A priori, we would expect that the ionization of a cation should require more energy than that required to generate the original cation:

`M(g) + Delta_1 rarr M^(+)(g) + e^-`, versus,

`M^(+)(g) + Delta_2 rarr M^(2+)(g) + e^-`

`Delta_2>Delta_1`, because the second ionization requires the removal of an electron that is bound by an already positive cation.

The given data reflect this change. It also reflects the electronic structure of the atom. For magnesium metal the first 2 electrons are removed from the valence (outermost) shell; the third electron is removed from an inner non-valence core, and the VAST difference in ionization energy reflects this.