Chapter 9, Problem 9.64QE

Interpretation Introduction

Interpretation:

Among ${\text{SCN}}^{-}$ or ${\text{CSN}}^{-}$ the more favored arrangement on the basis of formal charges has to be determined.

Concept Introduction:

Covalent bond is defined as a bond is formed from mutual sharing of electrons between atoms. Lewis structures are representations of the covalent bond. In this, Lewis symbols show how the valence electrons are present in the molecule.

The steps to draw the Lewis structure of the molecule are as follows:

Step 1: Find the central atom and place the other atoms around it. The atom in a compound that has the lowest group number or lowest electronegativity considered as the central atom.

Step 2: Estimate the total number of valence electrons.

Step 3: Connect the other atoms around the central atoms to the central atom with a single bond and lower the value of valence electrons by 2 of every single bond.

Step 4: Allocate the remaining electrons in pairs so that each atom can get 8 electrons.

The formula to calculate formal charge of the atom is as follows:

  $\text{Formal}\text{charge}=\left(\begin{array}{l}\text{number}\text{of}\\ \text{valence}\\ \text{electrons}\end{array}\right)-\left(\left(\begin{array}{l}\text{number}\text{of}\\ \text{lone pairs of}\\ \text{electrons}\end{array}\right)+\left(\frac{1}{2}\right)\left(\begin{array}{l}\text{number}\text{of}\\ \text{shared}\\ \text{electrons}\end{array}\right)\right)$

The different structures can be drawn for the same molecule. Structures that minimize the amount of formal charge found on each atom are more stable than structures that place large amounts of formal charge on atoms.

The structures that have adjacent atoms with formal charges of the same sign are less stable. Lewis structures that show the smallest formal charges are stable. The structure that has negative formal charges on the more electronegative atoms are favored.