What is Period 3 Element X Based on Given Successive Ionization Energies?

[Kelly09]

The succesive ionization energies in kj/mol of an element x found in period 3 of the periodic table are: 1800,3000,3600,5800,13200. With the aid of a periodic table,what is element x?

 

[pzona]

What do you already know about ionization energies that could help you figure this out?