Question

Arrange the following set of atoms in order of increasing ionization energy: Zn, Ga, K. Also discuss the reason.

Answer 1

According to periodic table, the elements Zinc, Gallium, and Potassium belongs to 4th period.  

The energy needed to remove the electrons present in the outermost shell of atoms are called ionization energy. The first ionization energy is very minimum energy compared to the second and third ionization energy. Because, there requires minimum energy to remove or eject the electron from the outermost shell which are loosely bond to the nucleus.  

The ionization energy of Potassium = 418.7 KJ/mol

The ionization energy of Zinc = 906.41 KJ/mol

The ionization energy of Gallium = 578.8 KJ/mol

Usually, from left to right along the period the ionization energy increases. But the ionization energy of gallium is lower than zinc because Zinc has a completely filled electronic configuration $\left[ Ar \right] { 3d }^{ 10 }{ 4s }^{ 2 }$ whereas gallium which starts filling p-orbitals $\left[ Ar \right] { 3d }^{ 10 }{ 4s }^{ 2 }{ 4p }^{ 1 }$. Because of completely filled configuration, zinc is stable and requires higher ionization energy whereas gallium is yet to fill its p-orbitals, so it has lower ionization energy compared to zinc.