Chapter 6, Problem 65A

(a)

Interpretation Introduction

Interpretation: It is to be explained why calcium has smaller second ionization than potassium.

Concept introduction:

The first ionization energy is the energy needed for the extraction of the outermost electron from the neutral gaseous atom. The second ionization energy is the energy needed for the extraction of the outermost electron from a unipositive gaseous atom.

Answer to Problem 65A

This is because, after removing the second electron, calcium will attain a noble gas configuration.

Explanation of Solution

After removing one electron, the electronic configurations of ${\text{K}}^{+}$ and ${\text{Ca}}^{+}$ are as follows:

  ${\text{K}}^{+}:1s^{2}2s^{2}2p^{6}3s^{2}3p^6$

  ${\text{Ca}}^{+}:1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^1$

As shown, ${\text{K}}^{+}$ has a noble gas configuration whereas ${\text{Ca}}^{+}$ requires the removal of 1 electron to attain a noble gas configuration. So, from ${\text{K}}^{+}$ , it is very difficult to remove an electron.

Thus, the second ionization energy of ${\text{Ca}}^{+}$ is much smaller than the second ionization energy of ${\text{K}}^{+}$ .

(b)

Interpretation Introduction

Interpretation: It is to be explained why lithium has larger first ionization energy than cesium.

Concept introduction:

The first ionization energy is the energy needed for the extraction of the outermost electron from the neutral gaseous atom.

Answer to Problem 65A

The first ionization energy decreases down the group.

Explanation of Solution

Lithium and cesium are present in the same group. Lithium is present in period 2 and cesium is present in period 6. Down the group, atomic size increases, and outermost electrons are less tightly held by the nucleus. So, less energy is required to remove the outermost electron.

Thus, the first ionization energy of lithium is larger than cesium,

(c)

Interpretation Introduction

Interpretation: It is to be explained why magnesium has a larger third ionization than aluminum.

Concept introduction:

The first ionization energy is the energy needed for the extraction of the outermost electron from the neutral gaseous atom. The second ionization energy is the energy needed for the extraction of the outermost electron from a unipositive gaseous atom.

Answer to Problem 65A

After removing the second electron, magnesium attains noble gas electronic configuration.

Explanation of Solution

Electronic configurations of Mg and Al are as shown:

  $\text{Mg}:1s^{2}2s^{2}2p^{6}3s^2$

  $\text{Al}:1s^{2}2s^{2}2p^{6}3s^{2}3p^1$

After removing two electrons from magnesium, it attains the configuration of Ne which is a noble gas, and so becomes stable.

It is very difficult to remove an electron from a stable ion or atom.

Thus, the third ionization energy of Mg is much larger than the third ionization of Al.