Question

The first ionization energies of alkaline earth metal are higher than of the alkali metals. Explain.

Answer 1

• Alkali metals have lowest ionization enthalpies in respective periods. This is because of their large atomic sizes.
• Also, they lose their only valence electron easily as they attain a stable noble gas configuration after losing it. Alkaline earth metals have smaller atomic size and higher effective nuclear charge as compared to alkali metals. This causes their first ionization enthalpies to be higher than that of alkali metals.
• However, their second ionization enthalpy is less than the corresponding alkali metals. This is because alkali metals, after losing one electron, acquires noble gas configuration, which is very stable.