Question

Arrange the elements Li, Na, K, Rb as required

Decreasing order of ionization energy

Answer 1

Step-1: Introduction

The ionization energy is defined as the minimum amount of energy required to remove an electron from the outermost shell of an isolated gaseous atom in its ground state to form a gaseous state. The ionization energy depends upon the atomic size, effective nuclear charge and screening effect of the inner electrons.

Step-2: Trend in periodic table

Within a period the ionization energy increases from left to right as the atomic number increases. Within a group the ionization energy decreases as the atomic number increases from top to bottom.

Step-3:

From Lithium ($\mathrm{Li}$) to Rubidium ($\mathrm{Rb}$), the ionization energy decreases due to increasing atomic number.

Step-4: Final answer

Therefore, the decreasing order of ionization energy is Lithium ($\mathrm{Li}$), Sodium ($\mathrm{Na}$), Potassium ($\mathrm{K}$) and Rubidium ($\mathrm{Rb}$).