Chapter 7, Problem 7.61P

(a)

Interpretation Introduction

Interpretation:

The Lewis structure, formal charges and resonance structures of ${\text{CS}}_{\text{3}}{}^{\text{2-}}$ has to be written.

Concept Introduction:

Lewis Structure:  A Lewis structure shows a covalent bond as pair of electrons shared between two atoms.

Procedure to write Lewis formulas:

1. 1) The symbols of the atoms that are bonded together in the molecule next to one another are arranged.
2. 2) The total number of valence electrons in the molecule is calculated by adding the number of valence electrons for all the atoms in the molecules.  If the species is an ion, then the charge of ion into account by adding electrons, if it is a negative ion or subtracting electrons if it is a positive ion.
3. 3) A two-electron covalent bond is represented by placing a line between the atoms, which are assumed to be bonded to each other.
4. 4) The remaining valence electrons as lone pairs about each atom are arranged so that the octet rule is satisfied for each other.

Formal charge (F.C):  The charges that assigned to each atom in a molecule or ion by a set of arbitrary rules and don not actually represent the actual charges on the atoms are called as formal charges.

The formal charge is calculated using the formula,

  $\text{F}\text{.C=Valence}\text{electrons-No}\text{of}\text{non-bonding}\text{electrons-}\frac{\text{No}\text{of}\text{bonding}\text{electrons}}{\text{2}}$

The Lewis structure with zero formal charge or least separated formal charges is the preferred structure of the molecule.

Resonance:  Each of the individual Lewis formulas is said to be a resonance form and the use of multiple Lewis formula is called resonance.  The two dashed lines taken together represent a pair of bonding electrons that spread over the two bonds.  Such a superimposed formula is called resonance hybrid because it is a hybrid of the various resonance forms.

(b)

Interpretation Introduction

Interpretation:

The Lewis structure, formal charges and resonance structures of ${\text{C}}_{\text{2}}{\text{O}}_{\text{4}}{}^{\text{2-}}$ has to be written.

Concept Introduction:

Refer to part (a).

(c)

Interpretation Introduction

Interpretation:

The Lewis structure, formal charges and resonance structures of ${\text{NCS}}^{\text{-}}$ has to be written.

Concept Introduction:

Refer to part (a).