SCIENCE · INVESTIGATE AND EXPLAIN

Separate resonance, formal charge and measured electron density

Preserve electron count and atom positions while changing a Lewis contributor.

Learning outcome: Compare all three double-bond sites for carbonate, then nitrate. Retain electron totals, every formal charge and the equal-contributor bond-order average.

Starting recap

Review the atomic electron ledger, signed energy changes and dimensional conversions. Distinguish a mathematical parameter from a unique material identification.

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Try

Carbonate has24 valence electrons; one double/two single contributor gives C formal0 and O formal0,−1,−1. Nitrate has the same electron total but central N formal+1.

Open the experiment

Predict

Does moving the drawn double bond require the nuclei to switch positions or the molecule to oscillate between drawings?

Your prediction and reason

Experiment

Compare all three double-bond sites for carbonate, then nitrate. Retain electron totals, every formal charge and the equal-contributor bond-order average.

Audit electron allocation across resonance contributors

Worked teaching model · synthetic values · Carbonate CO3²− and nitrate NO3− each have 24 valence electrons in the octet contributors shown: one double and two single central–O bonds, no central lone pair. Contributors differ only in electron allocation, not atom positions. Equal-contributor average is bookkeeping, not a molecule switching drawings.

Central atom: 0=C, 1=N: 0 choice Which oxygen has the double bond: 1 site

Reset keeps your prediction, captures and practice history.

Axes rescale with settings. Compare numerical values, not screen slopes. Discrete stems show steps, contributors or partial sums; connected samples show the declared parameter relationship, not a measured time trajectory.

Numerical diagram coordinates

oxygen site label	bond order in selected contributor
1	2
2	1
3	1

Schematic connectivity only, not a scale drawing or measured electron density. Parentheses show formal charge; lone-pair counts complete the octet allocation.

Selected octet contributor: total bond order at each site, nonbonding electrons and formal charge
Site	Total attached bond order	Nonbonding electrons	Formal charge
central C	4	0	0
O1	2	4	0
O2	1	6	-1
O3	1	6	-1

Three oxygen labels identify unchanged atomic sites. Selecting another double-bond site changes a contributor, not the positions of nuclei or a timed molecular switch.

Calculated values under declared assumptions
Quantity	Value	Unit
Total valence electrons	24	electrons
Bonding electrons	8	electrons
Nonbonding electrons	16	electrons
Sum of formal charges	-2	e
Equal-contributor central–O bond order	1.333333	ratio
Equal-contributor O formal allocation	-0.6666667	e

The electron total and net formal charge survive a change of contributor.

A single contributor has one formal double and two formal single bonds; three equivalent contributors distribute the representation over all O sites. Formal charge splits bond electrons equally and is not an experimentally unique partial charge. Nitrate central N carries +1 in these octet contributors, unlike carbonate central C.

Capture contrasting evidence and retain the interpretation limits. These supplied models do not identify an actual material or certify practical laboratory skill.

The electron total and net formal charge survive a change of contributor.

Observation to attach to a capture

Captures preserve recipes and replay their calculated results. They are synthetic model evidence, not physical measurements.

Understand

Build the electron budget before drawing

Carbonate has4+3×6+2=24 valence electrons. Nitrate has5+3×6+1=24. Start with the central atom bonded to three oxygen atoms, distribute remaining electrons and satisfy the second-period central octet. A contributor with one double bond and two single bonds uses eight bonding electrons and sixteen nonbonding electrons. A Lewis line represents an electron pair, not a photograph of a rod.

Allocate formal charge consistently

Formal charge equals neutral valence electrons minus nonbonding electrons minus half the bonding electrons. In carbonate, the central carbon receives four assigned bonding electrons and has formal charge zero. A double-bonded oxygen has four nonbonding and two assigned bonding electrons, giving zero. Each single-bonded oxygen has six nonbonding and one assigned bonding electron, giving−1. The sum is−2.

Compare an isoelectronic ion

Nitrate uses the same octet pattern but nitrogen has five neutral valence electrons, so its formal charge is+1. The oxygen pattern remains0,−1,−1, summing with nitrogen to−1. Same total electron count does not mean identical nuclear charges, total charge or every property.

Interpret three contributors

The formal double bond can be drawn to any one of the three equivalent oxygen sites. Changing the contributor moves only the electron allocation; it does not move nuclei. Equal weighting gives average central–oxygen bond order(2+1+1)/3=4/3. This summarizes a delocalized representation, not rapid switching among three distinct structures or a guarantee that every environment leaves the three sites equivalent.

Keep models distinct

Formal charge intentionally splits shared electrons equally. Electronegativity-based oxidation-state accounting does not. A partial atomic charge depends on how a continuous electron distribution is partitioned and is not uniquely identical to either integer label. Lewis/octet reasoning also has exceptions, including electron-deficient, odd-electron and expanded-valence representations. The workbench’s fixed carbonate/nitrate contributors do not claim to solve those cases. A correct report names the model before using its labels as evidence.

Evidence and safety boundary

Conceptual sources checked 30 October 2026: Formal charge and resonance, Lewis symbols and structures. All prose, numerical packets and diagrams are original; no textbook exercises or images are reproduced. The activity is supplied mathematical or synthetic evidence, not a performed materials experiment. No unknown substances, heating, high voltage or chemical synthesis are requested. Retain prior predictions and a changed-case explanation; numerical agreement alone does not certify independent understanding or practical competence.

Apply

Public practice checks a specific claim. It does not establish independent mastery.

Distinguish formal charge, oxidation state, partial charge and the limits of an octet representation.

Your explanation and limitations

Continue

Completion requires a saved prediction, at least one capture and a reflection. Presence checks do not grade your reasoning.

Skipping retains experiments and awards no mastery.

Previous: Infer a signed lattice term from a formation cycle Next: Explain metallic transport without overidentifying its cause

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