Question

Draw four reasonable resonance structures for the \(\mathrm{PO}_{3} \mathrm{~F}^{2-}\) ion. The central \(\mathrm{P}\) atom is bonded to the three \(\mathrm{O}\) atoms and to the \(\mathrm{F}\) atom. Show formal charges.

Short answer

Four possible resonance structures for the PO3F2- ion have been drawn considering P as the central atom bonded to three O atoms and one F atom, taking formal charges into account.

Step-by-step solution

Draw Central Atom and Surrounding Atoms

Firstly, a structure needs to be drawn with P atom as the central atom and three O atoms and one F atom surrounding it. Single bonds are drawn between the P and each of the other atoms initially.

Calculate and Assign Formal Charges

Formal charges are calculated by the formula: Formal charge = [# of valence electrons] - [(# of lone pair electrons) + 1/2(# bonding electrons)]. Assign these to all the atoms of the structure.

Draw First Resonance Structure

Form the first resonance structure by moving a pair of electrons from an oxygen atom next to the central phosphorus atom to create a double bond. Update the formal charges accordingly.

Draw Second Resonance Structure

Form the second resonance structure by moving a pair of electrons from the remaining single-bonded oxygen atom near the phosphorus atom to form a double bond. Update the formal charges again.

Draw Third and Fourth Resonance Structures

Draw the third and fourth resonance structures by considering movement of the lone pairs of electrons from the oxygen atoms of the double bonds to the phosphorous atom, and then the formation of a double bond between phosphorous and the fluorine atom. Each time, remember to update the formal charges.

Key concepts

Formal Charge Calculation

The concept of formal charge is essential for understanding how electrons are distributed in a molecule. Calculating formal charge helps us assign charges to atoms in Lewis structures.

• Use the formula: Formal charge = [# of valence electrons] - [(# of lone pair electrons) + 1/2(# bonding electrons)].
• This reveals whether an atom takes on a positive, negative, or neutral charge within a molecule.
• Ensuring minimal formal charges across a molecule often means greater stability of the structure.

Understanding formal charges provides insight into the most likely electron configurations and guides the drawing of resonance structures.

Lewis Structures

Lewis structures are crucial for visualizing the bonding between atoms in a molecule and the lone pairs of electrons that may exist. Here's how you can start drawing a Lewis structure:

• Identify the central atom, which is usually the least electronegative (except hydrogen).
• Place surrounding atoms and connect the central and peripheral atoms with single bonds.
• Distribute remaining electrons to satisfy the octet rule, where applicable, and count all bonding and lone pairs.

When drawing the \(\mathrm{PO}_{3} \mathrm{~F}^{2-} \) ion, phosphorus serves as the central atom surrounded by oxygen and fluorine.Understanding the balance of electrons can help identify possible resonance structures.

Chemical Bonding

Chemical bonding in molecules involves understanding how electrons are shared between atoms. Two main types of bonds in Lewis structures are:

• Single bonds, which involve the sharing of one pair of electrons.
• Double bonds, which involve two pairs of electrons shared between atoms.

In the context of a molecule like \(\mathrm{PO}_{3} \mathrm{~F}^{2-} \), both single bonds (to fluorine and one oxygen) and possible double bonds (with the other oxygens) need to be considered.The creation of double bonds, through resonance, helps satisfy each atom's octet and "spread" the negative charge more evenly across the molecule.

Phosphorus Oxoanion

The \(\mathrm{PO}_{3} \mathrm{~F}^{2-} \) ion is a type of phosphorus oxoanion, meaning it contains phosphorus bonded to oxygen. Here’s why they are important:

• These ions often have multiple resonance structures, showing potential electron configurations.
• Phosphorus oxoanions are commonly found in biological systems and play critical roles in energy storage and transfer, particularly in ATP and other biomolecules.
• The resonance structures help predict reactivity and stability of these ions in various chemical environments.

Understanding the resonance of a phosphorus oxoanion like \(\mathrm{PO}_{3} \mathrm{~F}^{2-} \) allows for a deeper insight into its chemical behavior and functions.