Learning targets

Georgia S8P1b — Develop and use models to describe the movement of particles in solids, liquids, gases, and plasma states when thermal energy is added or removed.
Target 1 · Particles in each state
  • I can describe how particles are arranged and how they move in a solid, a liquid, a gas, and plasma.
  • I can match a particle picture to its state.
Target 2 · Thermal energy and motion
  • I can explain what happens to particle motion when thermal energy is added or removed.
  • I can explain that temperature measures the average kinetic energy of the particles.
Target 3 · Changes of state
  • I can name the change between any two states (melting, freezing, vaporization, condensation, sublimation, deposition) and give a real example.
  • I can explain why a change of state is a physical change.
Target 4 · Heating curves
  • I can read a heating curve and say which state the substance is in on each part.
  • I can explain why the temperature stays flat while a substance melts or boils.

Three ideas: the kinetic molecular theory (8th grade version)

1. Everything is made of tiny particles.
Atoms and molecules, far too small to see. Even a rock is a pile of particles.
2. The particles are always moving.
Always. Even in a solid they are vibrating in place. Nothing is ever perfectly still.
3. More thermal energy = faster particles.
Heat something up and its particles speed up and spread out. Cool it down and they slow down and pull together. Temperature is a measure of the average kinetic energy of the particles.
Gas particles moving slowly in a container
Cooler gas: slower particles.
Gas particles moving fast in a warm container
Warmer gas: same particles, faster. That is all "hotter" means.
Two misconceptions to drop right now: (1) "Particles stop moving in a solid." No, they vibrate in place. (2) "Cold gets added to things." There is no such thing as adding cold. You can only add thermal energy or take it away.

The particle box: add energy, take it away, watch

Sixty particles of one substance. Drag the slider or use the buttons. Watch what changes and what stays the same.

less thermal energymore thermal energy

The four states, particle by particle

Solid
Particles packed tightly in neat rows
  • Packed tightly in a fixed pattern
  • Particles vibrate in place
  • Definite shape, definite volume
  • Lowest energy of the four
Liquid
Particles close together but loosely arranged
  • Close together but not in a pattern
  • Particles slide past each other
  • Takes the shape of its container, definite volume
  • Can flow and be poured
Gas
A few particles far apart, moving fast
  • Far apart, mostly empty space
  • Particles fly freely and bounce
  • No definite shape, no definite volume: fills the container
  • Easy to squeeze (compress)
Plasma
Charged particles with electrons stripped away
  • A gas with so much energy that electrons get knocked off
  • Particles are charged (ions and free electrons)
  • Glows, conducts electricity
  • Highest energy of the four
One substance, more and more thermal energy: tight grid (solid), loose blob (liquid), spread everywhere (gas).
Plasma facts
  • The most common state of matter in the universe. Every star, including the Sun, is plasma. Over 99% of the visible universe.
  • On Earth: lightning, neon signs, the northern lights, plasma TVs, the inside of a fluorescent bulb.
  • Not the plasma in blood. Same word, completely different thing. Blood plasma is a liquid.
  • The sequence solid → liquid → gas → plasma is just more and more thermal energy.

Changes of state

Click any arrow. Adding thermal energy moves you right (particles speed up and spread out). Removing it moves you left.

Click an arrow above.
Evaporation vs boiling
Both turn liquid into gas (both are vaporization). Evaporation happens only at the surface, at any temperature: a puddle dries on a warm day, sweat dries off your skin. Boiling happens throughout the liquid, only at the boiling point: bubbles of gas form inside the liquid and rise.
Every change of state is a physical change
Ice, liquid water, and steam are all H2O. The particles did not change; only how fast they move and how far apart they are. That is why you can always change back by adding or removing energy.
Same substance, three states. Only the energy is different.

Reading a heating curve

A heating curve is a graph of temperature (up) against time while you add heat steadily (across). Click each part of the line.

Click a segment of the line.
The surprise: students expect the temperature to always go up when you add heat. On the flat parts it does not. During melting or boiling, all the added energy is spent breaking particles out of their arrangement, not speeding them up. Ice water stays at 0°C until every bit of ice is gone. Then it climbs again.

One-minute videos

Simple Science, in about a minute each. Needs wifi.

States of matter (S8P1b)
Heating curves
Want to run the experiment? The Virtual Lab Bench has a Melt & Boil phase-change lab that draws the curve live.

How are you feeling about this today?

Nothing here is graded. Switch levels any time.

Printable worksheets

Student page first, answer key on the next page. Shuffle to pull a fresh set.

Standard and targets

Georgia S8P1b — Develop and use models to describe the movement of particles in solids, liquids, gases, and plasma states when thermal energy is added or removed. The particle box simulator and the particle pictures are the models. Heating curves are included because the Milestones-style questions lean on them and they connect to the same idea: energy in, motion up.

  • Target 1: particle arrangement and motion in all four states.
  • Target 2: thermal energy added or removed → particle speed; temperature as average kinetic energy.
  • Target 3: the six changes of state with examples; changes of state are physical.
  • Target 4: reading a heating curve; why the plateaus are flat.

How the levels differ

Level 1 · Coach
Two-choice questions with a coach line that says what to look for: how close are the particles, are they in a pattern, which direction did the energy go. Pictures on most items.
Level 2 · Guided
Four-choice: phase-change names from everyday examples, heating-curve segments by description, and true-or-false particle statements. Two hint layers, feedback that says why the wrong answer is wrong.
Level 3 · Challenge
Numbers: a substance with a given melting and boiling point, which state at a temperature, which segment of the curve, cooling curves, sublimation and deposition, and reasoning about the plateaus.

Classroom notes

  • Kinesthetic version: students are the particles. Shoulder to shoulder jiggling = solid. Walking around each other slowly in a group = liquid. Spread across the room, moving fast = gas. Four minutes, never forgotten.
  • Project the particle box and ask "what changed, what stayed the same?" as you drag the slider. The particle count never changes; that sets up conservation later.
  • Heating curve on the board: draw it live, narrating "climb... flat while melting... climb... flat while boiling." The flat parts are the surprise and the favorite test question.
  • Real-world hooks: sweat cools you because evaporation takes energy from your skin. Freezer frost is deposition. Dry ice fog at a haunted house is sublimation.
  • Misconceptions handled on the page: particles stop in a solid; cold is added; plasma is blood plasma; plasma is rare; temperature always rises when heating.
  • Nothing is collected: no names, no codes. Pairs with Unit 2 guided notes Part 2 and the Melt & Boil lab on the Virtual Lab Bench.