Question

Name the family with highest value of ionization enthalpy.

Answer 1

Cesium is said to have the lowest ionization energy and Fluorine is said to have the highest ionization energy. First ionization energy varies in a predictable way across the periodic table. The ionization energy decreases from top to bottom in groups, and increases from left to right across a period. Thus helium has the highest first ionization energy , and francium has one of the lowest.

It is because of the shielding effect that the ionization energy decreases from top to bottom within a group.