Explain each of the following observations using principles of atomic structure and/or bonding

a) Potassium has a lower first-ionization energy than lithium

K (1s²)(2s²,2p⁶)(3s²,3p⁶) (3d⁰) (4s¹) Z^* = 19 – (10 · 1.00 + 8 · 0.85) = 2.2

Li (1s²)(2s¹) Z^* = 3 - (2 · 0.35) = 2.3

Explanation not just in the difference in effective nuclear charge. As one can there is not much. The primary reason is related to the energy of a single s electron in the n = 4 level and the n = 2 level. The electron in the n = 4 level is higher in energy compared to an electron in n = 2 level and therefore is easier to remove.