Na has the largest 1st ionization energy (495) because the lone e- in the 3s
sublevel feels more of the pull from the nucleus in the Na atom. There are
fewer inner core e- shielding the 3s e- so more IE is needed to remove the
first e-. In the K atom, the 1st IE is smaller than that of Na (418 to 495).
Potassium is located in period 4, the e- is further from the nucleus, does not
feel the pull of the nucleus as tightly. The inner core e- are shielding the 4s
e- thus requiring less energy to remove the e-.
When totaling all IE for the electrons of the atoms, K has the greater total IE
because more e- are removed thus requiring more total energy.
K has the greater total IE because more e- are removed thus requiring more total energy.