Question

Write the resonance structure that would result from moving the electrons as the curved arrows indicate. Be sure to include formal charges if needed.

Answer 1

Hint: The resonance structures are two or more different structures of the same molecule or polyatomic ion that results from the delocalization of electrons and are represented by double-headed arrows. The movement of electrons is shown by curved arrows whose head should point towards the more electronegative atom.

Complete answer:
The properties and bonding of some molecules and compounds cannot be completely explained by a single Lewis structure and such compounds are found to have more than one contributing structure. The actual structure of these molecules is a hybrid of all the contributing structures and this phenomenon of possessing more than one Lewis structure is known as Resonance.
The structural difference arises due to the delocalization of electrons throughout the molecule but the total number of electrons remains the same in each contributing structure.
The contributing structures are known as canonical forms and are represented by doubly headed arrows between any 2 structures. The movement of electrons is represented by curved arrows heading towards more electronegative atoms.
The formal charges are hypothetical charges of an individual atom in a molecule or a polyatomic ion which is calculated to know the amount of charge residing on an atom in a molecule. It can be determined by the given formula:
\[\text{FC}=\text{V}-\left( \text{L+}\dfrac{\text{B}}{\text{2}} \right)\]
Where V is the number of valence electrons in an atom, L is the number of electrons present as lone pairs on an atom, and B is the number of electrons involved in bond formation.
The direction of arrows in the given structure of the molecule indicates that electrons will move away from the carbon and reside as lone pairs on oxygen atoms. So, the resonance structure will be drawn as follows:

Let us find out the formal charge on each atom.
\[\begin{align}
  & \text{FC on }\!\!'\!\!\text{ C }\!\!'\!\!\text{ }=4-\left( 0+\dfrac{6}{2} \right)=+3 \\
 & \text{FC on }\!\!'\!\!\text{ O }\!\!'\!\!\text{ }=6-\left( 6+\dfrac{2}{2} \right)=-1 \\
 & \text{FC on each }\!\!'\!\!\text{ H }\!\!'\!\!\text{ }=1-\left( 0+\dfrac{2}{2} \right)=0 \\
\end{align}\]
Hence, resonance structure along with formal charges is –

Note:
The individual resonance structure or canonical forms do not exist in reality but they are in rapid equilibrium with each other and thus the resonance hybrid is considered to be the actual Lewis structure of a molecule or a polyatomic ion.