Question

How does the Ionization energy of sodium (Na) compare to that of Potassium (K)?
(A) Ionization energy of K is less than Na because although there are more protons, K has 4 electron shells compared to Na which has 3 electron shells. This causes an increase in nuclear shielding, requiring less energy to remove the electrons.
(B) The ionization energy of K is more than Na because there are more protons and one extra electron shell in K. This causes an increase in the nuclear shielding and requires more electrons to remove the electron.
(C) The ionization energy of K is less than Na because there are fewer protons and one less electron shell. Since there is less attraction, it requires less energy to remove an electron.
(D) The ionization energies of both elements are equal because they are of the same group, the alkaline earth metals.

Answer 1

In order to compare the Ionization energy of Sodium and Potassium, we must have an idea about what an ionization energy is. Ionization energy is the measure of the difficulty in removing an ion from the outermost orbital of the atom or molecule.

Complete Solution:
Let us first understand what an Ionization energy is. Ionization energy is the minimum amount of energy which is required to remove an electron from the outermost orbital of the gaseous atom or molecule.
Let us now see about Sodium and Potassium. Sodium is a chemical element with the atomic number of 11 and it is represented by the symbol Na. Sodium belongs to the Group 1 and period 3. The electronic configuration of Sodium is $1{s^2}2{s^2}2{p^6}3{s^1}$. The electrons present per shell is 2, 8, 1. Therefore, there are totally 3 subshells.
- Potassium is a chemical element with an atomic number of 19 and it is represented by the symbol K. Sodium belongs to group 1 and period 4. The electronic configuration of potassium is given by $1{s^2}2{s^2}2{p^6}3{s^2}3{p^6}4{s^1}$. The electrons present per subshell is 2, 8, 8, 1. Therefore, there are 4 subshells. The major criteria for determining the Ionization potential is the effective nuclear charge. When the shielding effect increases the effective nuclear charge decreases. So, when compared to the sodium, potassium will be farther away from the nucleus as there are 4 subshells in potassium. While Sodium will be having only 3 subshells. Therefore, in potassium the nuclear force holding the potassium electron is very less. Therefore, it will require only less ionization potential compared to sodium.
So, the correct answer is “Option A”.

Note: We have to remember that certain factors will govern the Ionization energy such as
- when the force of attraction is stronger more Ionization energy will be required to remove an electron.
- when the nucleus is positively charged, the electron will get attracted strongly.
- when the outer electron remains close to the nucleus, the force of attraction will be greater compared to the one that is farther away.
- when there are a greater number of inner shells present, then the force of attraction will be weaker.