Problem 56 Write the Lewis structure, inclu... [FREE SOLUTION] (2024)

Chapter 2: Problem 56

Write the Lewis structure, including typical contributions to the resonancestructure (where appropriate, allow for the possibility of octet expansion),for (a) hydrogen phosphate ion; (b) bromite ion; (c) perchlorate ion; (d)arsenate ion.

Short Answer

Expert verified

For hydrogen phosphate ion (HPO4^2-), the Lewis structure includes a central phosphorus atom surrounded by four oxygen atoms with one double bond and a hydrogen atom bonded to one of the oxygen atoms. Bromite ion (BrO2-) has a bromine atom surrounded by two oxygens with one double bond. Perchlorate ion (ClO4-) involves a chlorine atom with four oxygen atoms, with resonance structures due to possible double bonds. Arsenate ion (AsO4^3-) has an arsenic atom surrounded by four oxygen atoms with double bonds and satisfies the expanded octet rule.

Step by step solution

- Identify Valence Electrons for Hydrogen Phosphate Ion (HPO4^2-)

To write the Lewis structure for the hydrogen phosphate ion \(HPO4^{2-}\), first count the total number of valence electrons. Phosphorus (P) has 5 valence electrons, each Oxygen (O) has 6, and Hydrogen (H) has 1. Since the ion carries a -2 charge, add 2 more electrons to the total count. Total valence electrons = \(5 + (6*4) + 1 + 2 = 32\) electrons.

- Draw the Basic Skeleton for Hydrogen Phosphate Ion

Place the Phosphorus (P) atom at the center, connect it with single bonds to four Oxygen (O) atoms, and place the Hydrogen (H) atom bonded to one of the Oxygen atoms since H can only form one bond.

- Add Electrons to Complete Octets

Place lone pairs around the Oxygen atoms to complete their octets. Oxygen atoms typically need 8 electrons in their outer shell. Two electrons are used in the bond with Phosphorus, so they each need six more from lone pairs.

- Add Double Bonds if Necessary

If there are any remaining electrons after the octets are completed, consider forming double bonds between the Phosphorus and any of the Oxygen atoms to satisfy the octet rule for Phosphorus.

- Ensure the Correct Formal Charge

Make sure the overall charge of the structure is -2, as this is the charge on the hydrogen phosphate ion. Adjust single and double bonds if necessary to attain the correct charge distribution.

- Draw Resonance Structures

Since double bonds can be formed to more than one Oxygen atom, draw resonance structures by moving double bonds between different Phosphorus and Oxygen pairs.

- Repeat Steps for Bromite Ion (BrO2-)

Follow similar steps as above to draw Lewis structures for bromite ion, including valence electron count (7 for Br + 6*2 for O + 1 for the negative charge = 20 electrons), constructing a basic skeleton with bromine at the center, completing the octets, and ensuring correct charge.

- Repeat Steps for Perchlorate Ion (ClO4-)

For perchlorate ion, count valence electrons (7 for Cl + 6*4 for O + 1 for negative charge = 32 electrons), draw Cl at the center with 4 O atoms around it, complete octets, add double bonds if necessary due to octet expansion with respect to Cl, and draw resonance structures.

- Repeat Steps for Arsenate Ion (AsO4^3-)

With arsenate ion, count the valence electrons (5 for As + 6*4 for O + 3 for the charge = 32 electrons), build the basic structure with As at the center, complete octets, ensure the overall charge is -3, form double bonds if needed, and draw possible resonance structures.

Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Valence Electrons

Valence electrons are the electrons that reside in the outermost shell of an atom and are available for bonding. As the 'social butterflies' of atoms, they can interact with valence electrons of other atoms to form chemical bonds.

For instance, while calculating the Lewis structure for the hydrogen phosphate ion \(HPO4^{2-}\), it’s essential to tally up these electrons. Phosphorus (P) brings five to the party, each Oxygen (O) arrives with six, and Hydrogen (H) only has one. Don't forget, since our ion is carrying a 'backpack' of -2 charge, we invite two extra electrons to ensure the balance. That's how we reach a total of 32 valence electrons needing to be arranged in the structure.

Octet Rule

The Octet Rule is like the golden rule of atomic stability - atoms strive to have eight electrons in their valence shell, much like most people aim to have a full set of utensils to enjoy a good meal.

When sketching out the basic skeleton for the hydrogen phosphate ion, each Oxygen seeks to fill its electron 'plate' with eight. Since bonding with Phosphorus has already offered them a portion (two electrons), they snatch six more from the 'buffet' of lone pairs. Phosphorus, being the generous sort, may share electrons via double bonds to make sure everyone, including itself, reaches the 'dining' satisfaction of a complete octet.

Resonance Structures

Picture a dance floor where pairs of dancers (atoms) can switch partners (bonds). Resonance structures are different snapshots of this molecular dance, where electrons 'boogie' between positions without altering the actual arrangement of atoms.

In the case of \(HPO4^{2-}\), after we give everyone their rightful share of electrons, we notice that Phosphorus can still cut a rug with more than one Oxygen - hence, we sketch several possible dance moves (resonance structures). These are not distinct entities but rather a blend, a 'remix', if you will, that better represents the molecule's electron arrangement.

Formal Charge

Formal charge is like balancing your checkbook - it helps you keep track of the 'electron economy' to ensure every atom gets its fair share. We calculate by taking the number of valence electrons an atom 'brought' minus the electrons it now 'owns' (half the bonded and all the nonbonded ones).

For our hydrogen phosphate ion friend, ensuring the correct formal charge is crucial for accurately depicting the molecule. With all atoms striving for the lowest possible formal charge, we may need to redistribute the bonding 'wealth', reflecting the ion's true charge, all while making sure our electron account doesn't dip into overdraft!

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