Warm-Up (5 min)
Hold up an ice cube, a glass of water, and a puff of visible "breath" on a cold morning. Ask: "These are all the same substance — H₂O — so why do they look and feel so different?" Collect student ideas on the board.
Direct Instruction (12 min)
Introduce the big idea: everything around us is made of tiny particles called atoms. Atoms of the same kind form an element (like oxygen or gold). Two or more different atoms bonded together form a compound (like water, H₂O). Explain that in a solid the particles are packed tight and vibrate in place; in a liquid they slide past each other; in a gas they zoom freely and fill any container.
Physical vs. Chemical Change (10 min)
Demonstrate two side-by-side tests. Test A (physical): stir sugar into warm water — it disappears but is still sugar (you could taste it or evaporate the water to get sugar back). Test B (chemical): mix baking soda + vinegar in a cup — bubbles form, the cup feels cooler, and a brand-new gas (carbon dioxide) is released. The original substances are gone.
Guided Experiment: Balloon Rocket-Fuel (15 min)
In teams of three, students pour 3 tablespoons of vinegar into an empty water bottle. They funnel 2 teaspoons of baking soda into a balloon, stretch the balloon over the bottle's mouth (keeping the powder in the balloon), then flip the balloon up so the baking soda drops in. The balloon inflates on its own as CO₂ gas is produced. Students record: what they saw, felt, and heard as evidence of a chemical reaction.
Journal & Closing (8 min)
Students draw before/after diagrams of the reaction with particle-level circles (baking soda + vinegar → water + salt + CO₂). Exit prompt: "Was inflating the balloon a physical or a chemical change? How do you know?" Preview tomorrow's lesson: mixtures, solutions, and how to separate them.
