Use matched subshells to explain PES shifts
You will be able to: Explain a matched-subshell energy shift using nuclear attraction and shielding.
Why can two atoms have similar peak patterns at different energies?
Two isoelectronic species can have the same subshell occupancies but different proton counts. Their spectra can therefore have the same idealized peak-size pattern while their binding energies differ.
A useful starting point: PES peak positions and sizes answer different questions →
Words and symbols before equations
- Matched subshell
- The same electron grouping compared across species, such as 1s in both.
- Isoelectronic comparison
- Equal electron counts and comparable configurations, isolating the effect of changing nuclear charge.
- Energy shift
- A change in peak position on a common binding-energy scale.
What this picture assumes
Schematic ten-electron species with reference energies 80, 15 and 5 arbitrary units and occupancies 2,2,6. Uniform energy scaling isolates a conceptual shift and does not predict real atomic spectra. Energy increases rightward.
Read the picture in three steps
- Identify the chemical species and the quantities each label or axis represents. Read the units and any scale assumptions before comparing values.
- Shifted 1s, 2s, 2p energies = 100, 18.75, 6.25 arbitrary units. Occupancy pattern stays 2:2:6.
- Check what the picture assumes below. Use the Explore task to predict one change before moving a control.
Connect the picture to the chemistry
First compare like with like: same subshell, same axis units and comparable conditions. A farther-right peak means more tightly bound only if energy increases rightward.
Within an isoelectronic series, increasing proton count generally increases attraction and electron binding energies. For example, Na⁺ has more protons than neutral Ne but the same ten-electron configuration.
The model overlays a ten-electron reference pattern and a uniformly scaled comparison. Uniform scaling is a teaching device, not a quantitative prediction of real spectra. Different subshells shift differently in experiments, and different electron counts can also change screening.
A worked example, step by step
Compare neutral Ne and Na⁺, both with 1s²2s²2p⁶. Predict the relative pattern sizes and which generally has greater binding energies.
- Both have subshell occupancies 2,2,6.
- Their idealized relative peak sizes therefore match.
- Na⁺ has 11 protons versus Ne’s 10 with the same electron count.
- Na⁺ generally binds those electrons more tightly, shifting corresponding peaks to higher binding energies.
Do not compare unmatched peaks or treat a schematic scale factor as measured atomic data.
Can peak positions shift without changing electron count?
Compare with an explanation
Yes. Nuclear attraction and shielding affect binding energies.
Predict. Change one thing. Explain.
Increase the comparison energy scale. Observe peak positions moving while the 2:2:6 count pattern remains unchanged.
On narrow screens, swipe or scroll diagrams sideways to read all labels.
Shifted 1s, 2s, 2p energies = 100, 18.75, 6.25 arbitrary units. Occupancy pattern stays 2:2:6.
Schematic ten-electron species with reference energies 80, 15 and 5 arbitrary units and occupancies 2,2,6. Uniform energy scaling isolates a conceptual shift and does not predict real atomic spectra. Energy increases rightward.
Explain what you noticed: Which quantity changed? Which stayed fixed? Use particle counts, mass or charge balance, electron structure, or nuclear attraction to justify your prediction. Separate an observation from an explanation.
Apply the idea to a fresh problem Practice →Show what you understand.
Two original questions are a starting check, not proof of mastery. Explain your choice before revealing the answer.
Original written challenge
4 points · self-check · not an official AP questionA schematic reference has 1s, 2s and 2p peaks at 80, 15 and 5 units, with occupancies 2,2,6. A comparison multiplies energies by 1.25. Calculate all positions, state the unchanged property and explain why this is not a real-spectrum prediction.
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Compare with the answer and four-point rubric
- 1 point: The shifted positions are 100, 18.75 and 6.25 units.
- 1 point: The relative occupancies remain 2,2,6.
- 1 point: A higher binding energy means more energy is needed to remove an electron.
- 1 point: Uniform scaling is a controlled teaching model; real subshell shifts need experimental or quantum-mechanical information.
Accept equivalent correct methods and explanations. This is a Refresh Kid teaching rubric, not an official AP scoring guideline.
Retrieve it before you reveal it.
RECALL 1What should be matched before comparing peaks?
Subshell identity and energy units/direction.
RECALL 2Does increased binding energy mean easier removal?
No; more energy is required.
RECALL 3Can a 2:2:6 pattern belong to more than one species?
Yes, such as isoelectronic Ne and Na⁺.
Revisit these tomorrow and a week later. Try a fresh problem and explain why the method applies.
Use matched subshells to explain PES shifts
- Compare the same subshell and labeled energy scale.
- Same occupancy can produce different binding energy.
Remember: Do not compare unmatched peaks or treat a schematic scale factor as measured atomic data.
Conditions: Schematic ten-electron species with reference energies 80, 15 and 5 arbitrary units and occupancies 2,2,6. Uniform energy scaling isolates a conceptual shift and does not predict real atomic spectra. Energy increases rightward.
Refresh Kid · AP Chemistry Unit 1 · Objectives 1.6.A · Review edition
Framework, scope and review status
Mapped to College Board CED, Topic 1.6, objectives 1.6.A. CED effective Fall 2024, current official file checked September 16, 2026, together with the published clarifications. This is Unit 1: Atomic Structure and Properties, Topics 1.1–1.8. The topic mapping identifies a framework area; focused lesson titles are our own teaching sequence. Molecular-formula scaling is an application of empirical composition. Models explicitly distinguish atom counts, molecule counts, mass fractions and electron structure. Spectra marked schematic are not measured data. Mass spectra here use single-element, singly charged monatomic ions. Configurations avoid Aufbau exceptions and individual quantum-number assignments. Qualitative attraction and size indices are not exact atomic predictions. The optional NaCl-type spatial block supplements complete charge-balance explanations. The lesson breakdown and questions are original Refresh Kid work, not official topic subdivisions.
Implementation and automated checks are separate from independent teacher review and observation of students. Both human review stages remain pending. This is a review edition, not a certified or validated assessment.
Optional further resource: College Board’s released questions and scoring guides. Papers can combine units; this link is an archive, not an assignment of every question to this lesson.
Our learn, explore, practice and recall sequence is informed by the IES learning guide. The exact Refresh Kid implementation has not been evaluated for learning effectiveness.
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