Blueprint — U4-S01 Evidence of change (Unit 4) — for James's approval
Read this in five minutes. It decides structure, order, check types and figure kinds; no sentence is drafted until you approve it. This is the FIRST Unit 4 blueprint — the sample you asked to review alongside the register. Nothing exists yet for Unit 4, so every part below is new; there are no keeps, splits or improve-only lessons. Seven lessons, one per atom (your one-lesson-per-atom ruling, 2026-07-31), atoms CRX-001–007. The particle-level WHY of this whole sequence is U4-S02 (CRX-008–012, decision D6's reorder) — it follows immediately and is not blueprinted here. The what/why pair inside this sequence is CRX-004 → CRX-005, placed back to back; CRX-004 stays one evidence-profile atom per decision D2.
Sources: unit4_design_v1.json (atoms CRX-001–007, sequence U4-S01, glossaryAudit, whatWhyCoverage), 02_lesson_architecture.md (direct-instruction pattern, gate U4-G1), 03_modality_map.md (six articles + one property_data_task), 05_operator_adoption.md (D2, D6). CED coverage: EK 4.1.A.1 and 4.1.A.2 under LO 4.1.A, confirmed by the Incept cross-check (ced_crosscheck_u4.json). All checks are authored fresh by write-mcqs after your approval; no mixed practice exists to inherit.
Lessons: 7. Teaching parts: 7, each one atom. Fluency-quiz rows: 3 (the three coined terms in this sequence: physical change, chemical change, precipitate — glossaryAudit). Figures stay macroscopic throughout: particle-level pictures are U4-S02's job (D6), so no drawing here shows molecules; formulas appear only as names retrieved from Unit 1.
Physical change L01new
A student leaves an open dish holding 50 g of water on a windowsill. A week later the dish is empty. The liquid water turned into water vapor in the room's air. The water looks gone for good. But every molecule of that vapor is still H₂O. Did the water stop being water?
The point, stated first. Can a substance change how it looks without changing what it is? Yes: the vapor in the air and the water in the dish are the same substance, H₂O. A change like this alters a substance's properties — its state, its shape, its temperature — but not its composition. A change that leaves the composition alone is called a physical change. The name matters because this unit's central question — did a NEW substance form? — starts by recognizing the changes that form nothing new.
Objective. CRX-001 — State that a physical change alters a substance's properties but not its composition; coin physical change
Objective. Fluency quiz: physical change (definition + recognize the definition applied to the dish scene)
Two families of physical change L02new
A student stirs 10 g of salt into 200 mL of water. The salt vanishes from view. Then the student boils the water away. At the bottom of the dish sits 10 g of white salt, unchanged. The mixing seemed to destroy the salt. The boiling gave the salt back, grain for grain. Did the salt or the water ever stop being salt and water?
The point, stated first. Which everyday changes leave every substance's composition alone? Two whole families do. Every phase change — melting, freezing, boiling, condensing — changes a substance's state and nothing else. Making a mixture, or separating one, moves substances together or apart without altering any of them. So both families are physical changes. Knowing the two families lets you classify most changes at a glance, before any other evidence arrives.
Objective. CRX-002 — Classify phase changes and the formation or separation of mixtures as physical changes
Chemical change L03new
A teacher passes an electric current through a dish of water. Gas bubbles stream up both wires. After ten minutes, 20 mL of gas sits above one wire and 10 mL sits above the other. Near a flame, the larger sample pops with a squeak — that gas is hydrogen. The smaller sample relights a glowing splint — that gas is oxygen. Neither gas behaves like water. Where did the water go?
The point, stated first. Can a change produce a substance that was not there before? The current turned water, H₂O, into two new substances: hydrogen gas, H₂, and oxygen gas, O₂. A change that transforms one substance into different substances is called a chemical change. A physical change leaves the composition alone. A chemical change replaces it. Every reaction in the rest of this unit is a chemical change, so this label names the unit's whole subject.
Objective. CRX-003 — State that a chemical change transforms substances into new substances, typically with different compositions; coin chemical change
Objective. Fluency quiz: chemical change against physical change — minimally different case pairs in one sentence frame
The electrolysis reaction stays in prose: the → arrow is coined at CRX-013 in U4-S03 (see call 1).
Four kinds of evidence L04new
A student pours 20 mL of one clear, colorless solution into 20 mL of another. The instant the liquids touch, a bright yellow solid appears and sinks through the mixture. Neither starting solution contained any solid. Neither starting solution was yellow. The student cannot see molecules, so the student cannot see directly whether a new substance formed. Which observations should count as evidence that one did?
The point, stated first. How can you spot a chemical change when molecules stay invisible? Four kinds of observation carry the evidence. The mixture can release heat or light. A gas can form. An insoluble solid can appear when two solutions mix — chemists call that solid a precipitate. A color can change. Each of the four is possible evidence that a new substance formed, and naming the type you saw is the skill every evidence question asks for.
Objective. CRX-004 — Identify heat or light, gas formation, precipitate formation, and color change as the four types of observation giving possible evidence of chemical change; coin precipitate (one evidence-profile part — decision D2)
Objective. Fluency quiz: precipitate + naming the evidence type from a fresh described observation
Why the evidence works L05new
The last lesson left a puzzle sitting in the beaker. Both starting solutions were colorless. The student added nothing else. Yet a bright yellow solid now rests at the bottom. A color cannot come from nowhere. Which substance in the beaker carries that yellow?
The point, stated first. Why can a color change, a gas, a solid, or released heat count as evidence of a chemical change? Because a chemical change produces new substances. A new substance brings its own properties. The yellow belongs to a substance that did not exist before the solutions mixed. The same logic covers all four observation types: a new gas, a new solid, a new color, or released energy can each be a new substance showing its properties. Read the observation as a property, and ask which substance owns that property.
Objective. CRX-005 — Explain why those observations can signal a chemical change: new substances bring different properties (released energy, a new gas, a new solid, a new color)
Possible, never proof L06new
A pan of water heats on a stove. At 100 °C the water bubbles hard. Gas streams up through the liquid. The last two lessons said a forming gas counts as evidence of a chemical change. But every bubble here holds plain water vapor — still H₂O, only hotter. The rule just called a physical change chemical. Can the four observations be trusted at all?
The point, stated first. Why does "a gas formed" not prove a chemical change? Because every one of the four observations can also accompany a purely physical change. Boiling makes bubbles with no new substance. Condensing releases heat with no new substance. So each observation is possible evidence, never proof. The honest verdict weighs the observation against both explanations: did a new substance form, or does a physical change explain the same sight? That judging skill is the next lesson's whole job.
Objective. CRX-006 — Explain why each observation is possible rather than conclusive evidence: the same signs can accompany purely physical changes
The verdict L07new
A shiny iron nail lies outdoors for a month. The nail turns brown and flaky. The nail's mass climbs from 5.0 g to 5.3 g, though nobody added anything to it. In the same month, a puddle beside the nail shrinks and vanishes. One of these two changes made a new substance. The other change did not. Which is which — and which observation settles each case?
The point, stated first. Given only what you can observe, how do you decide whether a change is chemical or physical? Start by naming the type of evidence: heat or light, a gas, a precipitate, or a color change. Then ask which explanation covers the observation better — a new substance, or the same substance in a new form. The nail's brown flakes are a new substance, built from iron and oxygen: a chemical change. The vanished puddle is the same water in a new state: a physical change. A verdict with its evidence named is exactly the answer AP Topic 4.1 asks you to produce.
Objective. CRX-007 — Judge whether a described change is chemical or physical from the observed evidence, naming the evidence type relied on (capstone; property_data_task; LO 4.1.A)
Gate note: U4-G1 sits after U4-S02 and requires CRX-007 plus the S02 capstones; its cold retention sample draws CRX-002, 004 and 006 from this sequence. No gate content is decided here.
What this blueprint cannot settle alone — your calls
1. No arrows in this sequence. The → arrow is coined at CRX-013 (U4-S03), and D5 treats a symbol before its defining atom as a defect. So the word-equation column is empty and the electrolysis and yellow-solid reactions stay in prose. Confirm, or license word equations with → early as exposure.
2. Figures stay macroscopic. Particle-level pictures belong to U4-S02 (D6's reorder); L01's drawing labels both panels "H₂O" as a name, with no molecules drawn. Confirm this boundary.
3. Fluency quizzes. Three coined terms get quiz rows (physical change, chemical change, precipitate — R233). L02 coins nothing; its check is itself a classifying fluency quiz. Does L02's quiz double as the recognition practice for L01's term, or do you want L01's quiz to carry classification items too?
4. L04 carries both a table and a drawing (the four-type table plus the yellow-solid scene). Both, or table only?
5. Verdict-plus-evidence in every L07 item. Your 2026-08-06 Unit 3 ruling says verdict+reason sparingly. Here the register's behaviour explicitly includes "naming the type of evidence relied on", so every item asks for it. Confirm that CRX-007 is the exception the ruling allows, or cap it at a subset.
6. The yellow-solid reagents stay anonymous ("two clear, colorless solutions") in L04/L05, because naming lead(II) nitrate and potassium iodide before equations or solubility exist adds load without payoff. Name them anyway, or keep them anonymous until U4-S05?
7. Scenes. The seven headaches use: evaporating dish, salt water separated, electrolysis, the yellow precipitate (twice, as its own why), boiling misfire, nail-and-puddle. Edit any scene in place and the lesson takes your wording.
Approve, edit lines in place, or name the lessons you want reshaped and I regenerate. write-lesson runs only after your word, taking this file as its spec.