Question

Why is `M(g) + Delta rarr M^(+)(g) + e^(-)` the ionization energy of magnesium?

Answer 1

Because that's how we specify the ionization energy.

Explanation:

Ionization energies are the energy associated with the formation of one mole of gaseous cations, and one mole of gaseous electrons, from one mole of gaseous atoms:

`M(g) rarr M^+(g) + e^(-)`; `DeltaE="ionization energy"`

Such a specification allows us to compare electronic structure on the basis of atoms, which allows an insight to atomic structure and energy levels, rather than the structure of a solid material. It is well know that ionization energies INCREASE across a Period (from left to right as we face the Table) and DECREASE down a Group.