_______ element has the lowest ionization energy.

By BYJU'S Exam Prep

Updated on: September 25th, 2023

(a) Sodium

(b) Helium

(c) Francium

(d) Caesium

The element that has the lowest ionization energy is Caesium. Ionization potential reduces as we move from lithium to cesium in the lower part of the group. The removal of an electron from Cs metal is the simplest.

Lowest Ionization Energy Element

Along the period (horizontally):

  • Caesium is the element having the lowest ionisation energy.
  • As we travel from lithium to cesium in the lower half of the group, the ionisation potential decreases. The simplest involves taking an electron out of Cs metal.

Down the group (vertically):

  • The electrons start going into higher energy shells as you move along the group. The force of attraction between the nucleus and its outermost electrons weakens as their distance from one another grows.
  • The ionisation energy lowers as you move down the group because it is simpler to remove electrons from the outermost shell.
  • It follows from the foregoing that elements with higher group numbers and lower period numbers will have greater ionisation energies.
  • Alkaline metals group I includes lithium, sodium, potassium, and cesium.
  • The atomic radii grow as we move down group 1 – A, which causes the ionisation potential to drop.


_______ element has the lowest ionization energy. (a) Sodium (b) Helium (c) Francium (d) Caesium

Caesium element has the lowest ionization energy. It reduces while moving from lithium to caesium. The potential of the ionisation decreases as we move from lithium to cesium in the lower half of the group in the periodic table.

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