Basic Concepts of Chemical Bonding

Resonance Structures


Resonance Structures

The Lewis structure of ozone (O3)

1. Sum of valence electrons = (6*3) = 18

2. Drawing the bond connectivities:

3. Complete the octets of the atoms bonded to the central atom:

4. Place any leftover electrons (18-16 = 2) on the central atom:

5. Does the central atom have an octet?

6. Does the central atom have an octet?

However... known facts about the structure of ozone

These Lewis structures are equivalent except for the placement of the electrons (i.e. the location of the double bond)

Equivalent Lewis structures are called resonance structures, or resonance forms

The correct way to describe ozone as a Lewis structure would be:

This indicates that the ozone molecule is described by an average of the two Lewis structures (i.e. the resonance forms)

The important points to remember about resonance forms are:

The Nitrate (NO3-) ion:

1. Count up the valence electrons: (1*5) + (3*6) + 1(ion) = 24 electrons

2. Draw the bond connectivities:

3. Add octet electrons to the atoms bonded to the center atom:

4. Place any leftover electrons (24-24 = 0) on the center atom:

5. Does the central atom have an octet?

6. Does the central atom have an octet?

Note: We would expect that the bond lengths in the NO3- ion to be somewhat shorter than a single bond


1996 Michael Blaber