Skill: atomise (audit mode) + ap-toolbox CED cross-check @ 1fed1da

Unit 4 — operator adoption of the parked decisions (option b, James 2026-09-24)

James chose option (b): the operator makes the register calls with his veto reserved; he checks the atomisation alongside. Each decision below is ADOPTED as stated unless he vetoes. One recommendation is FLIPPED on fresh evidence (D1); one carries a logged follow-up (D3).

CED cross-check (first live use of the Incept ap-toolbox, 2026-09-24)

The register maps all 21 Unit 4 essential-knowledge codes of the 2024–2025 CED, exactly — no gaps, no extras — across all nine topics (4.1–4.9). Source: ced-library.inceptstore.com apchem_enriched.json, diffed locally against unit4_design_v1.json mapsToStandards; result in ced_crosscheck_u4.json. (The whole-course /v1/analyze endpoint expects a nine-unit payload — noted for a later whole-course validation; unit-level diff is the meaningful check here.)

The six decisions

D1 — Percent yield: FLIPPED to INCLUDE. The original recommendation (exclude — no CED anchor) predates the exam-registry evidence: 2022 long FRQ Q1(b), 1 point, CED-tagged Unit 4 topic 4.5, asks the student to JUSTIFY a percent yield below 100% (dissolution during rinsing). James's meta-directive — bias toward what the actual AP asks — governs. Adopted: the two-atom letter-suffix insertion after CRX-046, shaped to the evidence (the real part is reasoning, not plug-in arithmetic): - CRX-046A (definition + calculation): "Calculate a percent yield as actual yield divided by theoretical yield times 100%." - CRX-046B (reasoning): "Explain why an actual yield can fall below the theoretical yield [e.g., product lost in rinsing or transfer, incomplete reaction], and justify whether a given percent yield is consistent with a described lab step." Implementation: in the first spec wave, with the validator run; percent yield comes OFF the explicitExclusions list. IDs letter-suffixed so the register stays stable.

D2 — Evidence categories as ONE profile atom: ADOPTED as recommended (Unit 3 v2 precedent; no separately-failable performance in splitting; documented exception to the enumeration-split signal).

D3 — Full redox balancing deferred to Unit 9: ADOPTED, with a follow-up logged. Checked today: Unit 9's register has the electrochemistry atoms (TEC-074–085 use half-reactions) but does NOT yet carry the deferred solution-balancing atoms (adding H₂O/H⁺/OH⁻) nor a retrieval treatment of CRX-080–084. FOLLOW-UP (blocking for the U9 build, not for U4): amend unit9_design with the balancing atoms + retrieval note before U9 specs are written.

D4 — Write/Balance verbs + equation_construction_task / equation_evaluation_task modalities + the pen-and-paper production contract: ADOPTED as recommended (mirrors James's drawing ruling; keeps the unit's core production behaviours visible to the modality layer and the production-item requirement).

D5 — Forward arrow (→) for ionization in Unit 4, ⇌ introduced in Unit 7: ADOPTED as recommended (a symbol before its defining atom is the AST-001 defect class; progressiveSharpening handoff carries the upgrade).

D6 — Reorder: particle-level basis (CED 4.4) immediately after evidence of change (4.1): ADOPTED as recommended (James's 2026-07-31 what-then-why ruling; JM-P15 authorizes departing from CED order; crosswalk keeps traceability; validator confirms no internal dependency violated).

What happens next (Build process v2)

On James's register sign-off (or silence + no veto on this record): blueprints per topic (unit4_build/blueprints/BLUEPRINT_<topic>.md) go to James for approval BEFORE any prose — starting with U4-S01 (evidence of change) as the sample; then write-lesson runs from approved blueprints; the question stage runs the Incept qgen trial (generated candidates vs authored, both through review-questions + blind read, James judges).

AP Chemistry Unit 4 — Decisions that need James

Status: Proposed for James's approval — phases 1–3 only. Six calls genuinely need your chemistry/curriculum judgment; everything else is settled by the principles, the 2026-07-31 rulings, or the Unit 2 precedent.

D1 — Percent yield: in Unit 4 or out?

Evidence. No Unit 4 EK names percent yield; EK 4.5.A.2 stops at "chemical calculations involving the mole concept." Limiting reactant and theoretical yield are likewise not verbatim in the EK text, but they are unavoidable subcomponents of the LO 4.5.A calculations the AP exam actually asks, so the register includes them (CRX-041–046, the draft's call, kept). Percent yield is the one member of that classic trio with no CED anchor at all — actual/theoretical comparison first appears in AP items through lab contexts. Recommendation. Exclude from Unit 4 (currently in explicitExclusions). If you want it taught with its natural neighbors, it is a two-atom insertion (definition + calculation) after CRX-046, and letter-suffix IDs keep the register stable.

D2 — The four evidence categories: one profile atom or four?

Evidence. CRX-004 keeps heat/light, gas, precipitate, and color change as ONE evidence-profile atom, with the reasons split out (CRX-005 why they signal change, CRX-006 why they are not conclusive). JM-P1a reads enumerations as split signals, but your Unit 3 v2 precedent keeps mechanism-free profiles single, and the CED gives no per-category mechanism here. The draft made the same call (its note #1). Recommendation. Keep the profile atom (documented exception in the design). Strict enumeration would add 3 atoms (84 → 87) with, in my judgment, no separately-failable performance — a student who can spot "gas formed = possible chemical change" and not "color change = possible chemical change" is an item-difficulty artifact, not a knowledge gap.

D3 — Redox balancing scope: defer H₂O/H⁺/OH⁻ balancing to Unit 9?

Evidence. EK 4.9.A.1 says only that redox equations "can be constructed from half-reactions." The register teaches: half-reaction definition, split, combine (electron-equalize and cancel), evaluate, and the end-to-end capstone (CRX-080–084) — all on reactions balanceable by inspection (metal/ion type). Full acidic/basic-solution balancing (adding H₂O, H⁺, OH⁻) is standard AP fare but the CED situates that machinery with electrochemistry, and teaching it here would demand aqueous-equilibrium vocabulary Unit 4 doesn't have. Recommendation. Defer to Unit 9 (currently an explicit exclusion + handoff note). Unit 9's build must then treat CRX-080–084 as retrieval and add the solution-balancing atoms there.

D4 — Verb and modality extensions for symbolic-equation construction

Evidence. Your unit note: "writing a balanced equation is a construction task on symbols; decide and document the modality." JM-P3's canonical verb list has no honest verb for it (Draw/Sketch would be false — nothing is drawn), and the six approved modalities have no symbolic-construction lane. The design proposes: verbs Write and Balance (10 atoms); modalities equation_construction_task (10 atoms) and equation_evaluation_task (3 atoms); and an assessment contract mirroring your drawing ruling — equation-option MCQ with deterministic renders plus at least one pen-and-paper production item per construction atom (stem explicitly instructs writing the full equation on paper; reveal shows model answer + species/states/coefficients/atom-balance/charge-balance checklist, gated behind a student action). The validator enforces Write/Balance ⇔ equation_construction_task exactly as it enforces Draw/Sketch ⇔ diagram_construction_task. Recommendation. Approve all three pieces (verbs, modalities, contract). The alternative — filing these under article — would hide the unit's core production behaviours from the modality layer and from the production-item requirement.

D5 — Ionization equations: forward arrow now, reversible arrow later?

Evidence. The draft wrote HNO₂ + H₂O ⇌ NO₂⁻ + H₃O⁺. But ⇌ carries equilibrium meaning that is taught in Unit 7 and the partial-ionization story in Unit 8 — using it in Unit 4 is a symbol before its defining atom (the same defect class as the AST-001 forward reference). CRX-074 therefore writes ionization with →, and the Unit 7 handoff upgrades the notation (progressiveSharpening). The cost: students briefly see NH₃ + H₂O → NH₄⁺ + OH⁻ without the caveat that the reaction is far from complete; the CED itself defers that caveat ("relative strengths compared" is the only strength content here, kept qualitative in CRX-077/078 with supplied data). Recommendation. Forward arrow in Unit 4, reversible arrow introduced properly in Unit 7. If you prefer AP-authentic notation immediately, the alternative is a one-line notation gloss inside CRX-074's lesson ("the double arrow means the reaction does not go to completion — you'll study this in Unit 7"), at the price of a forward reference.

D6 — Topic order: 4.4 (particle-level basis) immediately after 4.1

Evidence. Your 2026-07-31 ruling: teach a property's what and why together in the same unit, what first, why immediately after. In CED order, the observable what (Topic 4.1, evidence of change) is separated from its particle-level why (Topic 4.4, bonds vs intermolecular attractions) by equations and particulate models. The register re-orders: U4-S01 (CRX-001–007, evidence) → U4-S02 (CRX-008–012, particle basis), then equations. JM-P15 authorizes departing from CED topic order; the CED crosswalk keeps traceability. Cost: CRX-009/010 need Unit 3 IMF atoms as prerequisites slightly earlier in the unit; no Unit-4-internal dependency is violated (verified by the validator). Recommendation. Approve the re-order. It also gives the U4-G1 gate a coherent "what change is, and why" scope before the symbolic machinery starts.

AP Chemistry Unit 4 — Expert Atomisation Audit and Behaviour Register

Status: Proposed for James's approval — phases 1–3 only. Date: 2026-08-03 Structured source of truth: unit4_design_v1.json (register prefix CRX, Chemical Reactions)

Principles and lexicon notes (read first)

• Governed by JM_atomization_principles.md (JM-P1..P24 incl. the JM-P1a enumeration corollary) and every 2026-07-31 ruling in Content_Quality_Feedback_Master_Log.md: one lesson per atom; no interactive articles; drawing atoms assessed by image-option MCQ plus at least one pen-and-paper production item; what and why taught together in the same unit, what first; per-variable qualitative atoms before any genuinely new multivariable equation.
• Canonical mechanism lexicon (JM-P13). Unit 4 uses three entries, all already registered in the 21-entry lexicon embedded in 10_kc_tree_units1-9.pipeline.json, verbatim wherever they recur:
• MECH-ATOM-CONSERVE — "because atoms are neither created nor destroyed in a chemical change, so every element's atom count is identical before and after" (CRX-016, CRX-035; the unit's backbone mechanism)
• MECH-PROTON-TRANSFER — "because the reaction transfers one or more protons (H⁺) from a donor species to an acceptor species" (CRX-057; recurs in Unit 8)
• MECH-ELECTRON-TRANSFER — "because the reaction transfers one or more electrons from the species that is oxidized to the species that is reduced" (CRX-062; recurs in Unit 9)
• Jargon before use (JM-P12). Every technical term is bound to a defining atom in the design's glossaryAudit (46 entries) — locally (e.g., spectator ion → CRX-027) or to an approved earlier-unit atom (particulate model → CSP-013; mole → AST-001) or to a pending Unit 3 KC-tree id (molarity → KC-3.7.A.2-b). "Precipitate" is glossed inline at first appearance (CRX-004) and treated formally at CRX-066, matching the draft's handling.
• Verb lexicon extension (pending James, decision D4). Two atoms' behaviours cannot be honestly named by the JM-P3 canonical verbs: symbolic-equation construction opens with Write or Balance (10 atoms). Writing a balanced equation is a construction task on symbols, not a drawing — per James's unit-note instruction to classify the behaviour honestly. Only CRX-032 (a genuine drawing) uses Draw.
• IDs. Sequential per-unit register CRX-001…CRX-084; letter-suffix insertions reserved for James-directed additions (Unit 1/2 convention). The id column below keeps James's blind-pass EK-anchored convention (KC-<EK>-<letter>, x = LO-level capstone) with the register mapping alongside.

Audit of the existing draft (11_unit4_atoms_v1.md) against the principles and rulings

The draft (72 KCs, 2026-07-17) predates the 2026-07-31 rulings and the Unit 2 v2.4 granularity standard. Its structure was largely sound — behaviour-first statements, bracketed examples, forward/inverse splits, three correct lexicon entries — and all 72 draft behaviours survive. The re-audit changed the following.

Net: 72 draft KCs → 84 register atoms (12 additions, 0 deletions, several rewordings and re-orderings). Additions: CRX-005, 013, 014, 019, 020, 022, 030, 037, 042, 044, 078, 083.

Deliberately retained groupings (documented exceptions)

Cross-unit consumption (never cloned)

• Unit 1 (AST): mole machinery AST-004/005/008 (retrieved, per the unit note — never re-taught), AST-002 (mole), AST-012, AST-013, AST-020, AST-053, AST-055, AST-055A.
• Unit 2 (CSP v2.4): CSP-002 (covalent bond), CSP-005 (polar bonds), CSP-012 (cation/anion), CSP-013 (particulate model), CSP-014 (crystal lattice), CSP-063 (lone pairs).
• Unit 3 (register not yet built): nine pending KC-tree cross-references (KC-3.1.A.x-a, KC-3.1.A.3-c, KC-3.3.A.x-a, KC-3.8.A.1-a, KC-3.7.A.2-b/c/d, KC-3.4.A.1-a/b), recorded in unitHandoff.pendingCrossReferences for re-pointing when the Unit 3 register exists.

Full behaviour register — blind-pass review format

Presented in teaching order of topics (4.1 → 4.4 → 4.2 → 4.3 → 4.5 → 4.6 → 4.7 → 4.8 → 4.9; the 4.4-after-4.1 re-order is decision D6). Types: concept · quant · rep · reason · data.

Topic 4.1 Introduction for Reactions (LO 4.1.A; EK 4.1.A.1-2) - 7 KCs

Topic 4.4 Physical and Chemical Changes (LO 4.4.A; EK 4.4.A.1-2) - 5 KCs

Topic 4.2 Net Ionic Equations (LO 4.2.A; EK 4.2.A.1-3) - 19 KCs

Topic 4.3 Representations of Reactions (LO 4.3.A; EK 4.3.A.1) - 3 KCs

Topic 4.5 Stoichiometry (LO 4.5.A; EK 4.5.A.1-3) - 17 KCs

Topic 4.6 Introduction to Titration (LO 4.6.A; EK 4.6.A.1) - 5 KCs

Topic 4.7 Types of Chemical Reactions (LO 4.7.A; EK 4.7.A.1-5) - 13 KCs

Topic 4.8 Introduction to Acid-Base Reactions (LO 4.8.A; EK 4.8.A.1-3) - 10 KCs

Topic 4.9 Oxidation-Reduction (Redox) Reactions (LO 4.9.A; EK 4.9.A.1) - 5 KCs

Summary

• 84 atoms from 9 LOs / 21 EKs (30 official CED rows, all covered); 10 capstones, one or two per LO along the LO's own axis (LO 4.4.A keeps the draft's i/ii capstone pair).
• Type mix: 34 concept · 14 quant · 17 rep · 18 reason · 1 data — the rep/quant weight (31 production/calculation atoms) reflects the unit's identity as the course's central skills unit, and the 18 reason atoms carry the what/why-together ruling.
• 14 instructional sequences, 5 gates (see 02_lesson_architecture.md); every capstone gated; final gate interleaves prior domains.
• Pilot pair: CRX-056 (titration analysis — calculation_heavy, per James's unit note) and CRX-033 (particulate diagram → equation — conceptual_data_heavy, stress-testing deterministic particulate figures plus the proposed symbolic-equation assessment contract).
• Validation: validate_design.py PASS, 0 errors, 0 warnings (validation_report.json, computed).

Judgment calls parked for James

Six, in 04_decisions_for_james.md: D1 percent yield in/out; D2 evidence-category granularity; D3 redox balancing scope (H₂O/H⁺/OH⁻ deferral to Unit 9); D4 Write/Balance verbs + equation-task modalities and their assessment contract; D5 forward arrow vs ⇌ for ionization equations; D6 the 4.4-after-4.1 re-sequencing.

Revision log

AP Chemistry Unit 4 — Instructional Architecture

Status: Proposed for James's approval — phases 1–3 only. Structured source of truth: unit4_design_v1.json

Architecture judgement

The order follows dependency and the what/why-together ruling, not CED topic-heading order: observable change classification is followed immediately by its particle-level basis (Topic 4.4 material moved up — decision D6); symbolic-equation conventions are established before any routine consumes them; balancing precedes ionic forms, which precede particulate translation; qualitative mole-ratio reasoning precedes every calculation chain; limiting-reactant analysis precedes theoretical yield; solution and gas conversions precede the multi-step capstone and titration; reaction-class identification (proton transfer, electron transfer, precipitation) precedes the Brønsted-Lowry and half-reaction constructions that deepen two of those classes.

The 14 sequences are teaching arcs, not lessons. One lesson per atom (James's ruling, 2026-07-31, reaffirming 2026-07-21): every one of the 84 atoms gets its own lesson; an atom may span more than one lesson, never fewer; no shared lesson surfaces. Sequences exist for ordering, hooks, and gate placement only.

Teaching sequence

Direct-instruction pattern within an atom

1. Retrieve only the prerequisite knowledge this behaviour needs ("You've already seen…" — exposure phrasing, never mastery claims).
2. State the behaviour and its boundary in student language.
3. Model one worked example with the decision cues visible; calculations use the approved question-first scaffold (Values / Equation / [Make X the subject] / Substitute + Calculate), one algebraic step per line, only where a formula is substituted.
4. Use a minimally different example or non-example.
5. Fade support into an independent, atom-labelled check.
6. Route failure to that atom or its prerequisite, never to a whole-topic re-teach.

Stoichiometry lessons retrieve the Unit 1 mole atoms (AST-004..008) and Unit 3 molarity/gas atoms; they never re-teach them (James's unit note).

Ordering decisions that protect cognitive load

• The why-arc (U4-S02) lands immediately after the what-arc (U4-S01), inside the same unit — no deferral of mechanisms to a later unit.
• Equation anatomy and state symbols (CRX-013/014) precede every atom that reads or writes an equation.
• Check-balance (CRX-019) and why-coefficients-only (CRX-020) precede the balancing production (CRX-021); construction precedes evaluation for every representation (equations, ionic forms, particulate drawings, redox constructions).
• Qualitative proportionality (CRX-037) precedes the first quantitative ratio atom (CRX-038); each conversion family runs forward before inverse (CRX-039→040, 047→048, 049→050).
• Limiting-reactant definition and why (CRX-041/042) precede identification (CRX-043) and yield (CRX-045/046); the multi-step capstone (CRX-051) closes the arc only after every component routine.
• Oxidation/reduction definitions and the oxidation-number codebook precede redox identification (CRX-062), which precedes combustion and the classification capstone.
• Solubility knowledge (CRX-067) arrives before precipitate prediction (CRX-068); earlier net-ionic tasks supply solubility information in the stem (scope decision).

Gate architecture

Gates are slim checkpoints, not lessons. Every LO has a gated capstone; the final gate interleaves prior domains so success cannot come from short-lived blocked practice.

Gate items stay atom-labelled and 4-option MCQ where MCQ is used (AP-exam mimicry exception). Construction atoms sampled at gates pair a verifiable image-option or equation-option MCQ with the atom's production evidence, per the drawing/symbolic assessment contracts.

Forward handoff

• Unit 5 consumes balanced equations and mole ratios (CRX-021, CRX-036).
• Unit 6 consumes the bond-energy account of chemical change (CRX-011) and the mass chains (CRX-039, CRX-046).
• Unit 7 upgrades CRX-074's forward-arrow ionization equations to reversible-arrow equilibrium statements (decision D5).
• Unit 8 consumes the whole Brønsted-Lowry foundation (CRX-070..079) and titration arc (CRX-052..056) as retrieval, then quantifies (Ka, pH, curves).
• Unit 9 consumes the redox machinery (CRX-058..063, CRX-080..084) and adds electrochemical context plus acidic/basic balancing (decision D3).
• Pending cross-references: nine Unit 3 KC-tree ids are wired as prerequisites and recorded in unitHandoff.pendingCrossReferences; they must be re-pointed at Unit 3 register ids when that register is built.

Approval boundary

Architecture is ready for pilot specification only. No lesson content, questions, media, or generation calls exist or are authorized by this package.

AP Chemistry Unit 4 — Modality Map

Status: Proposed for James's approval — phases 1–3 only. Structured source of truth: unit4_design_v1.json

Recommendation

Modality is assigned per atom from the required student behaviour, never by pipeline default. Unit 4 is the course's central symbolic-skills unit, so its distinctive load is symbolic-equation construction — balancing, ionic forms, proton-transfer equations, half-reactions. James's unit note asked for an honest classification of these Draw/Sketch-adjacent behaviours: writing a balanced equation is a construction task on symbols, not a drawing. Rather than mislabel them as articles or drawing tasks, this design proposes two named modality extensions (decision D4).

Modality distribution by sequence

Assessment contracts for construction behaviours

• Drawing (CRX-032), per James's 2026-07-31 ruling: image-option MCQ with deterministically rendered options, plus at least one pen-and-paper production item — the stem explicitly instructs the student to draw the representation on paper (the AP exam requires free-hand drawing); a student action then reveals a model answer and a feature checklist (particle ratios, intact species, atom conservation) for self-check. The reveal is never visible beneath the question.
• Symbolic equations (proposed, D4), mirroring that contract: equation-option MCQ with deterministically rendered candidate equations (correct sub/superscripts, states), plus at least one pen-and-paper production item — the stem explicitly instructs the student to write the complete equation on paper (the AP exam requires hand-written equations); reveal shows the model equation plus a checklist (species, states, coefficients, atom balance, charge balance). If the platform later offers reliable symbolic entry, it can replace the MCQ half; the production half stays.
• Evaluation atoms (equation_ and diagram_evaluation_task) are natural MCQs — discriminating the flaw in a supplied representation — and carry misconception-keyed distractors.
• Numeric routines (all quant atoms) use numeric entry with the sig-fig feedback tier; gate items may deliberately be 4-option MCQ for AP mimicry.

Pilot pair

Both pilots must pass review before any scaled generation; approval of this package authorizes only these two pilot specifications.

Asset and interaction controls

• Precision-bearing visuals: deterministic SVG/HTML only — particulate models, dissociation pictures, titration apparatus, annotated equations. Figure specs pin every label, count, and value; figure captions/alt text are student-visible fields under the standing sweeps.
• Generative imagery: not approved for precision-bearing instruction.
• Video, simulation, game: none in the initial Unit 4 build.
• Interactive articles: zero (ruling above); the validator enforces this.
• Equations in prose: every canonical equation also stands alone on a display line with a symbol key; one canonical equation per relationship, inverses by rearrangement; arrow-chain route summaries stay banned. Reaction arrows (→) in chemical equations are, of course, chemistry content, not banned operation arrows.