Chapter 4.5, Problem 7PPA

Write electron configurations for (a) O²⁻, (b) Ca²⁺, and (c) Se²⁻.

Interpretation Introduction

Interpretation: The electronic configuration for the given ions should be determined.

Concept Introduction:

Periodic Table: The available chemical elements are arranged considering their atomic number, the electronic configuration and their properties. The elements placed on the left of the table are metals and non-metals are placed on right side of the table.

In periodic table the horizontal rows are called periods and the vertical column are called group.

There are seven periods and 18 groups present in the table and some of those groups are given special name as follows,

$\begin{array}{l}\text{Group-1}\to \text{Alkali metal}\\ \text{Group-2}\to \text{Alkaline metals}\\ \text{Group-16}\to \text{Chalcogens}\\ \text{Group-17}\to \text{Halogens}\\ \text{Group-18}\to \text{Noble gases}\end{array}$

Atomic Number: Atomic number of the element is equal to the number of protons present in the nucleus of the element which is denoted by symbol Z. The superscript presents on the left side of the symbol of the element.

Cation: Removal of electron from the atom results to form positively charged ion called cation.

Anion: Addition of electron to atom results to form negatively charged ion called anion.

The net charge present in the element denotes the presence or absence of electrons in the element.

Electronic configuration: It is used to represent the distribution of electrons placed over orbitals that present in the atom.

The rules followed by the electrons are as follows,

The electrons gets distributed strictly following the order starting from lower energy orbital to higher energy orbital(Aufbau principle), pairing of electrons in subshell starts only when all the orbitals in the subshell are singly filled (Hund’s Rule) and finally, no two electrons that have same set of quantum numbers (Pauli’s Exclusion Principle).

Answer to Problem 7PPA

Answer

1. (a) The electronic configuration for ${\text{O}}^{\text{2-}}$ is $1s^{2}2s^{2}2p^6$

Explanation of Solution

Explanation

Analyze the period table and determine the number of electrons present in the given ion ${\text{O}}^{\text{2-}}$.

Examining the periodic table says that the atomic number of $\text{O}$ is 8 that is it contains 8 electrons but the given ${\text{O}}^{\text{2-}}$ ion has two extra electrons which totally gives 10 that has to be distributed over the orbitals present in the sub-shells following the above three rules.

Therefore, the electronic configuration for the given element ${\text{O}}^{\text{2-}}$ is $1s^{2}2s^{2}2p^6$

Interpretation Introduction

Interpretation: The electronic configuration for the given ions should be determined.

Concept Introduction:

Periodic Table: The available chemical elements are arranged considering their atomic number, the electronic configuration and their properties. The elements placed on the left of the table are metals and non-metals are placed on right side of the table.

In periodic table the horizontal rows are called periods and the vertical column are called group.

There are seven periods and 18 groups present in the table and some of those groups are given special name as follows,

$\begin{array}{l}\text{Group-1}\to \text{Alkali metal}\\ \text{Group-2}\to \text{Alkaline metals}\\ \text{Group-16}\to \text{Chalcogens}\\ \text{Group-17}\to \text{Halogens}\\ \text{Group-18}\to \text{Noble gases}\end{array}$

Atomic Number: Atomic number of the element is equal to the number of protons present in the nucleus of the element which is denoted by symbol Z. The superscript presents on the left side of the symbol of the element.

Cation: Removal of electron from the atom results to form positively charged ion called cation.

Anion: Addition of electron to atom results to form negatively charged ion called anion.

The net charge present in the element denotes the presence or absence of electrons in the element.

Electronic configuration: It is used to represent the distribution of electrons placed over orbitals that present in the atom.

The rules followed by the electrons are as follows,

The electrons gets distributed strictly following the order starting from lower energy orbital to higher energy orbital(Aufbau principle), pairing of electrons in subshell starts only when all the orbitals in the subshell are singly filled (Hund’s Rule) and finally, no two electrons that have same set of quantum numbers (Pauli’s Exclusion Principle).

Answer to Problem 7PPA

Answer

1. (a) The electronic configuration for ${\text{Ca}}^{2+}$ is $\left[\text{Ne}\right]3s^{2}3p^6$

Explanation of Solution

Explanation

Analyze the period table and determine the number of electrons present in the given ion ${\text{Ca}}^{2+}$.

Examining the periodic table says that the atomic number of $\text{Ca}$ is 20 that is it contains 20 electrons but the given ${\text{Ca}}^{2+}$ ion is in short of two electrons which results in 18 electrons that has to be distributed over the orbitals present in the sub-shells following the above three rules.

Therefore, the electronic configuration for the given element ${\text{Ca}}^{2+}$ is $\left[\text{Ne}\right]3s^{2}3p^6$

Interpretation Introduction

Interpretation: The electronic configuration for the given ions should be determined.

Concept Introduction:

Periodic Table: The available chemical elements are arranged considering their atomic number, the electronic configuration and their properties. The elements placed on the left of the table are metals and non-metals are placed on right side of the table.

In periodic table the horizontal rows are called periods and the vertical column are called group.

There are seven periods and 18 groups present in the table and some of those groups are given special name as follows,

$\begin{array}{l}\text{Group-1}\to \text{Alkali metal}\\ \text{Group-2}\to \text{Alkaline metals}\\ \text{Group-16}\to \text{Chalcogens}\\ \text{Group-17}\to \text{Halogens}\\ \text{Group-18}\to \text{Noble gases}\end{array}$

Atomic Number: Atomic number of the element is equal to the number of protons present in the nucleus of the element which is denoted by symbol Z. The superscript presents on the left side of the symbol of the element.

Cation: Removal of electron from the atom results to form positively charged ion called cation.

Anion: Addition of electron to atom results to form negatively charged ion called anion.

The net charge present in the element denotes the presence or absence of electrons in the element.

Electronic configuration: It is used to represent the distribution of electrons placed over orbitals that present in the atom.

The rules followed by the electrons are as follows,

The electrons gets distributed strictly following the order starting from lower energy orbital to higher energy orbital(Aufbau principle), pairing of electrons in subshell starts only when all the orbitals in the subshell are singly filled (Hund’s Rule) and finally, no two electrons that have same set of quantum numbers (Pauli’s Exclusion Principle).

Answer to Problem 7PPA

Answer

The electronic configuration for ${\text{Se}}^{2-}$ is $\left[\text{Ar}\right]3d^{10}4s^{2}4p^6$

Explanation of Solution

Explanation

Analyze the period table and determine the number of electrons present in the given ion ${\text{Se}}^{2-}$.

Examining the periodic table says that the atomic number of $\text{Se}$ is 34 that is it contains 34 electrons but the given ${\text{Se}}^{2-}$ ion has extra two electrons which results in 36 that has to be distributed over the orbitals present in the sub-shells following the above three rules.

Therefore, the electronic configuration for the given element ${\text{Se}}^{2-}$ is $\left[\text{Ar}\right]3d^{10}4s^{2}4p^6$