Question

Explain the first ionization energy of lithium is greater than that of sodium

Answer 1

Lithium is an entire energy level smaller than sodium. Because of this, the electrons are more strongly attracted to the protons in the nucleus. The more energy levels you have, the easier it is to pull valence electrons from the outer energy shell, therefore, sodium has a smaller first ionization energy than lithium.
Source(s):
General Chemistry I Class in college

Answer 2

I agree with the response by v. Here is another way of saying the same thing.
Li has +3 charge in nucleus and 2e in the first energy level; therefore, the outside electron "sees" +1 charge.
Na has 11+ charge in nucleus and the outside electrons "sees" 1" charge. Since the one electron is farther away in Na, it is easier to split off so it requires less energy to pull it away.

Answer 3

Lithium Has a small atomic radius than sodium hence the valence electron are strongly attracted by the positive nuclear which require alot of energy to remove the valence electron