# Why is there a large increase between th first and second ionization energies of the alkali metals?

Jan 9, 2017

Because the valence shell of the alkali metal contains ONE electron only........

#### Explanation:

Two factors are important here. $\text{A priori}$ we would expect that it would be harder to remove an electron from a cation than from a neutral species. This is from simple considerations of electrostatics.

Neverthless, the alkali metals metals contain only the one valence electron. Ionization of an ${\text{M}}^{+}$ ion requires that the electron be removed from an inner shell, that is closer to the metal nucleus, and therefore much more strongly held:

$M \left(g\right) + {\Delta}_{1} \rightarrow {M}^{+} \left(g\right) + {e}^{-}$

${M}^{+} \left(g\right) + {\Delta}_{2} \rightarrow {M}^{2 +} \left(g\right) + {e}^{-}$

${\Delta}_{2} \text{>>} {\Delta}_{1}$

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