Chapter 7, Problem 7.71QE

(a)

Interpretation Introduction

Interpretation:

The electron configuration of elements with two unpaired electrons and with an atomic number less than 10 has to be determined.

Concept Introduction:

The electronic configuration is defined as the distribution of electrons in various atomic orbitals of the atom. The electrons that are present in an outermost orbital are known as valence electrons whereas those present in the orbitals with lower quantum numbers are called core electrons. The general outer electronic configuration of $s\text{ block}$ elements is $n{s}^{1-2}$, that of $p\text{ block}$ elements is $n{s}^{2}n{p}^{1-6}$, that of $d\text{ block}$ elements is $\left(n-1\right)d^{1-10}n{s}^{0-2}$ and that of $f\text{ block}$ elements is $\left(n-2\right)f^{1-14}\left(n-1\right)d^{0-10}n{s}^2$.

Electrons are filled in orbitals in accordance with three rules: Aufbau principle, Hund’s rule, and Pauli’s exclusion principle. Aufbau principle states that electrons are filled in the orbitals from lower to higher energy level as follows:

  $1s<2s<2p<3s<3p<4s<3d<4p<5s<4d<5p<6s<4f<5d<6p<7s$

Hund’s rule states that initially each orbital is singly occupied and then pairing occurs and Pauli’s exclusion principle states that the spin of two electrons in one orbital is always different.

Explanation of Solution

The electronic configuration for elements with an atomic number less than 10 is as follows:

$\begin{array}{cc}\text{Atomic number }\left(\text{Z}\right)& \text{Electron configuration}\\ 1& 1s^1\\ 2& 1s^2\\ 3& 1s^{2}2s^1\\ 4& 1s^{2}2s^2\\ 5& 1s^{2}2s^{2}2p^1\\ 6& 1s^{2}2s^{2}2p^2\\ 7& 1s^{2}2s^{2}2p^3\\ 8& 1s^{2}2s^{2}2p^4\\ 9& 1s^{2}2s^{2}2p^5\\ 10& 1s^{2}2s^{2}2p^6\end{array}$

According to Hund’s rule, initially each orbital is singly occupied and then pairing occurs in the filling of an electron in same subshell.

Therefore, the two unpaired electrons are present in $2p$ subshell in atomic number 6 and 8 as follows:

(b)

Interpretation Introduction

Interpretation:

The electron configuration of element with the largest number of unpaired electrons and with an atomic number less than 10 has to be determined.

Concept Introduction:

Refer to part (a).

Explanation of Solution

The electronic configuration for elements with an atomic number less than 10 is as follows:

$\begin{array}{cc}\text{Atomic number }\left(\text{Z}\right)& \text{Electron configuration}\\ 1& 1s^1\\ 2& 1s^2\\ 3& 1s^{2}2s^1\\ 4& 1s^{2}2s^2\\ 5& 1s^{2}2s^{2}2p^1\\ 6& 1s^{2}2s^{2}2p^2\\ 7& 1s^{2}2s^{2}2p^3\\ 8& 1s^{2}2s^{2}2p^4\\ 9& 1s^{2}2s^{2}2p^5\\ 10& 1s^{2}2s^{2}2p^6\end{array}$

According to Hund’s rule, initially each orbital is singly occupied and then pairing occurs in the filling of an electron in same subshell.

Therefore, the most unpaired electrons are contained by an element that has atomic number 7. The number of unpaired electrons is 3 and it is represented as follows:

(c)

Interpretation Introduction

Interpretation:

The electron configuration for those elements that have only two occupied subshells with an atomic number less than 10 has to be determined.

Concept Introduction:

Refer to part (a).

Explanation of Solution

The electronic configuration for elements with an atomic number less than 10 is as follows:

$\begin{array}{cc}\text{Atomic number }\left(\text{Z}\right)& \text{Electron configuration}\\ 1& 1s^1\\ 2& 1s^2\\ 3& 1s^{2}2s^1\\ 4& 1s^{2}2s^2\\ 5& 1s^{2}2s^{2}2p^1\\ 6& 1s^{2}2s^{2}2p^2\\ 7& 1s^{2}2s^{2}2p^3\\ 8& 1s^{2}2s^{2}2p^4\\ 9& 1s^{2}2s^{2}2p^5\\ 10& 1s^{2}2s^{2}2p^6\end{array}$

The elements that have occupied only two subshells are the elements with atomic number 3and 4.