An ionization level is the amount of energy required to remove an electron from a bound stationary state, in other words, from its orbit around the nucleus of a particular atom. 

Select one of the following ways to remember the way ionization levels generally behave when looking at the elements on the periodic table:

• Ionization levels generally decrease as go left and down on the periodic table, OR
• Ionization levels generally increase as you go right and up the periodic table.