Question

What is potassium's ionization energy?

Answer 1

In the periodic table, the ionization energy of an element decreases when the atomic size of the element increases. This is due to the shielding effect. As atomic size increases, the force of attraction between the nucleus and the valence electrons present in the outermost orbital decreases, because of the presence of inner shells.

Complete step-by-step answer: The measure of the ability of electrons to be held in its place or measure of the struggle for removing the electrons from the atom is termed as ionization energy.
Lithium is the first element present in group 1. Its ionization energy is 520 kJ/mol.
Sodium is the second element present just below lithium. Its first ionization energy is 498 kJ/mol.
Potassium is the third element present below sodium.
Rubidium is the fourth element present below potassium. Its first ionization energy is 403 kJ/mol.
Cesium is the fifth element present below rubidium. Its first ionization energy is 376 kJ/mol.
As potassium is present between the elements, sodium and rubidium, its first ionization energy will be between 496 kJ/mol and 403 kJ/mol.
Thus, the first ionization energy of potassium is 419 kJ/mol.

Note: As we move down the group in the periodic table, the atomic size increases due to the increase in the number of shells. When the ionization energy of an element is high, then the removal of the electron will become more difficult.