   Chapter 9, Problem 57IL

Chapter
Section
Textbook Problem

Draw the two resonance structures that describe the bonding in SO2. Then describe the bonding in this compound using MO theory. How does MO theory rationalize the bond order of 1.5 for the two S—O bonds in this compound?

Interpretation Introduction

Interpretation:

The two resonance structures of SO2 and bonding in this compound has to be given using MO theory and also has to describe how the MO theory rationalize the bond order of 1.5

Concept Introduction:

Molecular orbital (MO) theory:  is a method for determining molecular structure in which electrons are not assigned to individual bonds between atoms, but are treated as moving under the influence of the nuclei in the whole molecule.

According to this theory there are two types of orbitals,

1. (1) Bonding orbitals
2. (2) Antibonding orbitals

Electrons in molecules are filled in accordance with the energy; the anti-bonding orbital has more energy than the bonding orbitals.

Fractional bond order: The molecules which have resonance structures possess fractional bond order.

Bond order between any bonded pair of atoms X and Y:

Resonance:

• Sometimes the chemical bonding of a molecule cannot be represented using a single Lewis structure. In these cases, the chemical bonding are described by delocalization of electrons and is known as resonance.
• All the possible resonance structures are imaginary whereas the resonance hybrid is real.
• These structures will differ only in the arrangement of the electrons not in the relative position of the atomic nuclei.
Explanation

Two resonance structures are possible for SO2 which contribute equally to the hybrid structure.

The total number of valence electrons is 18

For the three bonds present, 6 electrons are needed.

Remaining 12 electrons are distributed as lone pair of electrons.

Therefore, the resonance structures of SO2 molecule are:

Bond order of SO bonds:

Bond order for the compounds having resonance structures can be calculated by the general equation:[If the bond pair have the atoms X and Y]

Bondorder=numberofsharedpairs

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