Which element requires the least i. e. potassium or gallium why

Potassium

General Formulas and Concepts:

Chem

Explanation:

The Periodic Trend for 1st Ionization Energy is increasing up and to the right. That means He would have the highest I.E and therefore take the most amount of energy to remove an electron.

Potassium and Gallium are both in Period 4. Potassium is element 19 and Gallium is element 31.

Potassium's electron configuration is [Ne] 4s¹ and Gallium's electron configurations is [Ne] 4s²3d¹⁰4p¹. Since both are in Period 4, they have the same number of core e⁻. Therefore, the shielding effect is the same.

However, since Gallium is element 31, it has 31 protons compared to Potassium, which is element 19 and has 19 protons. Gallium would have a greater Zeff than Potassium as it has more protons. Therefore, the FOA between the electrons and nucleus of Ga is much stronger than that of K. Thus, Ga requires more energy to overcome those FOA to remove the 4p¹ e⁻. Since K has less protons, it will have a smaller Zeff and thus less FOA between the e⁻ and nucleus, requiring less energy to remove the 4s¹ e⁻.