Chapter 5.1, Problem 9SP

(a)

Interpretation Introduction

Interpretation: The electron configuration for the boron atom needs to be written and the number of unpaired electrons present in it needs to be determined.

Concept Introduction: The electron configuration explains the electron distribution in atomic orbitals. There is a standard notation to write an electron configuration. The atomic shell is written in a sequence with the number of electrons in superscript.

Answer to Problem 9SP

  $1s^{2}2s^{2}2p^1$ , one unpaired electron.

Explanation of Solution

The given atom is boron. It belongs to group 13 with atomic number 5. Since s orbital can maximum hold 2 electrons, the electronic configuration is represented as follows:

  $B\left(5\right)=1s^{2}2s^{2}2p^1$

To determine the number of unpaired electrons, the atomic orbitals can be drawn as follows:

  

Now according to Hund’s rule, the filling of electrons in orbitals takes place in such a way that every orbital is singly occupied before any orbital is doubly occupied by electrons. Also, according to the Pauli-exclusion principle, two electrons in the same orbital must have opposite spins.

Now, electrons are filled as follows:

  

There is 1 unpaired electron in the 2p orbital; thus, the number of unpaired electrons will be 1.

(b)

Interpretation Introduction

Interpretation: The electron configuration for the silicon atom needs to be written and the number of unpaired electrons present in it needs to be determined.

Concept Introduction: The electron configuration explains the electron distribution in atomic orbitals. There is a standard notation to write an electron configuration. The atomic shell is written in a sequence with the number of electrons in superscript.

Answer to Problem 9SP

  $1s^{2}2s^{2}2p^{6}3s^{2}3p^2$ , two unpaired electrons.

Explanation of Solution

The given atom is silicon. It belongs to group 14 with atomic number 14. Since the maximum electrons hold by s and p orbitals are 2 and 6 respectively. The electronic configuration is represented as follows:

  $\text{Si}\left(14\right)=1s^{2}2s^{2}2p^{6}3s^{2}3p^2$

To determine the number of unpaired electrons, the atomic orbitals can be drawn as follows:

  

Now according to Hund’s rule, the filling of electrons in orbitals takes place in such a way that every orbital is singly occupied before any orbital is doubly occupied by electrons. Also, according to the Pauli-exclusion principle, two electrons in the same orbital must have opposite spins.

Now, electrons are filled as follows:

  

There are 2 unpaired electrons in the 3p orbital; thus, the number of unpaired electrons will be 2.

(c)

Interpretation Introduction

Interpretation: The electron configuration for the sulfur atom needs to be written and the number of unpaired electrons present in it needs to be determined.

Concept Introduction: The electron configuration explains the electron distribution in atomic orbitals. There is a standard notation to write an electron configuration. The atomic shell is written in a sequence with the number of electrons in superscript.

Answer to Problem 9SP

  $1s^{2}2s^{2}2p^{6}3s^{2}3p^4$ , two unpaired electrons.

Explanation of Solution

The given atom is sulfur. It belongs to group 16 with the atomic number 16. Since the maximum electrons hold by s and p orbitals are 2 and 6 respectively. The electronic configuration is represented as follows:

  $\text{S}\left(16\right)=1s^{2}2s^{2}2p^{6}3s^{2}3p^4$

To determine the number of unpaired electrons, the atomic orbitals can be drawn as follows:

  

Now according to Hund’s rule, the filling of electrons in orbitals takes place in such a way that every orbital is singly occupied before any orbital is doubly occupied by electrons. Also, according to the Pauli-exclusion principle, two electrons in the same orbital must have opposite spins.

Now, electrons are filled as follows:

  

There are 2 unpaired electrons in the 3p orbital; thus, the number of unpaired electrons will be 2.