What does the ionization energy quantitatively measure about an atom?

1 Answer
Oct 30, 2015

#M(g) + Delta rarr M^+(g) + e^-#


As shown, ionization energy is the energy associated with the formation of 1 mol gaseous cations, and 1 mol of gaseous electrons, from 1 mol of gaseous element.

Ionization energies tend to follow a Periodic Trend. They increase across a Period, and decrease down a Group. Why should this be so?