Unit 06 · Matter & Chemistry arc · 8th grade
The invisible
crowd.
Everything around you is made of tiny particles in constant, directionless motion. You can't see them — but you can smell them, catch them shoving pollen, and watch them spread on their own. Three proofs, one conclusion.
the smell that crosses the room
The phenomenon · the lab
The Smell That Crosses the Room
Nobody carries the smell across the room — no fan, no breeze, no courier. Yet the back row smells the popcorn within a minute. Something travels by itself. Release the particles and watch diffusion do its slow, unstoppable work.
Odor particles leave the bag and random-walk — bump, turn, bump, turn — drifting from the crowded corner toward the empty one. That's diffusion: movement from high concentration to low concentration, powered by nothing but the fact that particles never sit still.
The model · three rules
The particle model of matter
Everything is particles
All matter — desk, air, beetle, you — is built from tiny particles: atoms and molecules, the same cast from Unit 05.
They never stop moving
Every particle jiggles, constantly, forever. More energy moves them faster, less slows them down — but never to zero. Even a rock's particles vibrate in place.
There's space between them
Particles don't touch wall to wall — there's room between them. Lots of space in gases, some in liquids, barely any in solids. (Next stop: the three states of matter, explained by exactly this.)
The case file · catching the invisible
Three proofs you can't unsee
The smell
Popcorn odor crosses a still room in a minute. Nothing carries it — it diffuses. If particles weren't real and moving, the back row would starve in ignorance.
The jiggle
1827: Robert Brown watches pollen in water and it never stops jittering. 1905: Einstein explains it — invisible water molecules shoving the pollen. Brownian motion: particles caught in the act.
The spread
One drop of food coloring in a still glass of water. No stirring. An hour later the whole glass is tinted. The color moved on its own — diffusion again, this time in a liquid.
Standard: MS-PS1-1 — the particle model of matter (NGSS Lead States, 2013). DCI: PS1.A Structure and Properties of Matter. CCC: Scale, Proportion, and Quantity — the evidence is visible at our scale; the explanation lives at theirs.
Myth-busters · tap to flip
Unlearn these three things
Manipulative · Spaced repetition
Say it like a scientist
Twelve words. Flip the card, grade yourself honestly, and the deck schedules your next review — hard words come back sooner. Come back tomorrow and it remembers you. (It lives in your browser, no account.)
flip the card, then grade yourself
Practice · Math skills
The smell race
Motion math, but the moving thing is invisible: time the smell, compute the rate, and resolve the 500 m/s paradox with collisions and zigzags. Print it, solve it, check the key.
Exit ticket · 5 questions
Before you leave the room
No grade, no stakes — just proof the particles moved. Answer all five to earn the stamp.
You can't see them. You can smell them.
Same particles — next stop, three moods.