Question

Which element has the highest ionization potential and which has the lowest ionization potential?
A.He, Cs
B.Cs, He
C.Li, Ar
D.H, He

Answer 1

Ionization potential also called ionization energy. The energy required for removing an electron from an isolated atom or molecule. The ionization energy of a chemical element expressed in joules and volts. This energy is measured by the capability of an element to enter into chemical reactions requiring ion formation or donation of electrons.

Complete step by step answer:
He has $1{s^2}$ electron structure. The electron is being removed from the same orbital as in hydrogen’s value of ionization energy is much higher than hydrogen, because the nucleus has 2 protons attracting the electrons instead of 1. Cs is 7 the less electronegative of the two. Ionization energies are dependent upon the atomic radius. Since going from right to left on the periodic table, the atomic radius increases, and the ionization energy increases from left to right in the periodic table. Alkali metals have the lowest ionization potential. The ionization energy of an element increases as one moves across a period in the periodic table because electrons are held tighter by the higher effective nuclear charge.

Hence, option (A) is correct answer.

H has the highest and Cs has the lowest ionization energy.

Note: The number of energy levels increases as you move down a group as the number of electrons increases. Each subsequent energy level is further from the nucleus than the last. The atomic radius increases as the group and energy level increases. For this reason, ionization potential is defined.