"Ionization energy is like "electron greed".How badly does the atom what to hold on to its electron?Lower I.E. means it is easier (takes less energy) to remove an electron from the atom and create an ion. Higher I.E. means it is more difficult (takes more energy) to remove and electron from the atom and create an ion."

The more greedy the atom is for the electron, the more energy it will take to remove it.