SCIENCE · INVESTIGATE AND EXPLAIN

Build an orbital occupancy ledger with charge and spin constraints

Connect nuclear identity, electron count, orbital capacity and Hund filling within a declared small-atom domain.

Learning outcome: Compare Z=8 charges 0 and−1, then compare different proton counts with the same electron count. Retain box occupancies and identify Pauli/Hund constraints separately.

Starting recap

Review amount and charge accounting, dimensions and inverse-model assumptions. A fitted number or diagram is not a unique physical identification.

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Try

Neutral oxygen has eight electrons:1s²2s²2p⁴. Its three 2p boxes contain one opposite-spin pair and two unpaired electrons in the simple ground-state model.

Open the experiment

Predict

Does making an O²− ion change proton count or only electron count?

Your prediction and reason

Experiment

Compare Z=8 charges 0 and−1, then compare different proton counts with the same electron count. Retain box occupancies and identify Pauli/Hund constraints separately.

Reconcile proton charge and orbital occupancy

Worked teaching model · synthetic values · Formal3–19-electron bookkeeping using1s,2s,2p,3s,3p,4s order and simple ground-state Hund filling. Some proposed ions may be unstable; the diagram does not establish existence or chemical favorability. Transition-metal ordering, spin–orbit coupling and configurations beyond this domain are excluded.

Nuclear proton count: 8 protons Ion charge: 0 elementary charges

Reset keeps your prediction, captures and practice history.

Formal orbital box representation — not spatial boxes
Subshell	Spatial orbital occupancy
1s	↑↓
2s	↑↓
2p	↑↓↑↑

Calculated values under declared assumptions
Quantity	Value	Unit
1s population	2	electrons
2s population	2	electrons
2p population	4	electrons
Total electrons	8	electrons
Nuclear protons	8	protons
Charge from proton minus electron count	0	elementary charges

Changing charge changes electron count, not nuclear identity.

Within this limited s/p domain, fill degenerate orbitals singly with parallel spin before pairing, and use at most two opposite spins per orbital. The construction is a model bookkeeping exercise, not proof that every chosen ion is a stable species.

Retain predictions, contrasting captures and a changed-case explanation. No graph or numerical match certifies independent reasoning or a performed spectroscopy experiment.

Changing charge changes electron count, not nuclear identity.

Observation to attach to a capture

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

Understand

Start with charge conservation

Proton count identifies the nucleus. Electron count is proton count minus signed ionic charge, in elementary-charge units. A positively charged ion has fewer electrons than protons; a negative ion has more. Changing charge does not change one element into another. Species with the same electron count can still have different nuclei, binding energies and sizes.

Build the limited configuration

The model uses the low-energy sequence 1s,2s,2p,3s,3p,4s for its restricted electron counts. Each s subshell contains one spatial orbital; each p subshell contains three. Capacity is two electrons per spatial orbital. The order is a model of a limited domain, not a universal proof that an orbital with lower n always has lower energy in every atom or ion.

Apply two different rules

Pauli exclusion allows at most two opposite spin projections in one spatial orbital. Hund filling for degenerate orbitals favors singly occupied orbitals with parallel spins before pairing in this simple ground-state representation. These are different constraints. A p box arrangement could obey capacity while still representing an energetically inappropriate pairing pattern for the assumed ground state.

Work the oxygen count

At Z = 8 and charge zero, eight electrons fill 1s²2s²2p⁴. The 2p entries are one pair and two single electrons in the displayed Hund arrangement. At charge −1 there are nine electrons and 2p⁵, with two pairs and one single. The nucleus remains Z = 8. The drawing labels occupancies, not literal square regions in space or tracks of spinning particles.

Compare isoelectronic cases

Z = 10, charge zero and Z = 13, charge +3 both yield ten electrons in this limited ledger. That equivalence does not imply the same element or equal orbital energies. Different nuclear attractions matter. State exactly which observation—electron count or nuclear identity—each piece of evidence supports.

Transfer and domain limits

A formal Z = 18, charge −1 entry gives nineteen electrons and begins 4s occupancy in this bookkeeping rule. The tool does not claim that such an ion is a stable isolated ground-state species. Transition-metal exceptions, electron removal order in d-block ions and spin–orbit effects require a broader treatment. A valid arithmetic label is not automatically a physically realized material.

Sources and model boundary

Conceptual references checked 30 October 2026: OpenStax electronic structure, OpenStax quantum theory. All lesson prose, numerical packets and diagrams are original; no textbook figures or exercises are copied. Synthetic parameter choices are not measured atomic spectra. The activity does not request radiation sources, vacuum equipment, particle beams or chemical manipulation. Saved calculations remain public practice, not independent mastery or physical laboratory evidence.

Apply

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

Explain why an allowed bookkeeping configuration does not establish stable-ion existence or a universally valid filling rule.

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: Interpret a radial probability distribution without inventing an orbit Next: Separate binding-energy evidence from detector-response assumptions

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