The Particle Model of Matter: a full term of science

Ten ready-to-teach lessons for Year 7 Chemical sciences. Print this pack and the term is prepared: every lesson comes with a step-by-step plan, the questions to ask, a student worksheet, cut-out cards, a station sheet or exit tickets, an assessment kit and worked answers.

Start here: five minutes to Monday

1. Skim the term at a glance on the next page.
2. Print the lesson you need. Each lesson is three A4 sheets: plan, worksheet, and cards, a station sheet or tickets.
3. Gather the few items under “You need” on the plan. Most come from the science prep room or the supermarket.
4. Open the free interactive unit on your board or projector. Every plan tells you which picture to show and when.
5. Teach straight from the plan. Timings, talk prompts, misconceptions and worked answers are all on the one page.

For any Year 7 science teacher

The pack suits a science specialist and a teacher working outside their own subject alike: each plan explains the idea in plain words, lists the misconceptions students bring, and gives worked answers. The big idea of the term: everything is made of tiny particles that are always moving and that attract one another, with empty space between them. How the particles are arranged, how fast they move and how strongly they hold on decide whether a substance is a solid, a liquid or a gas, and explain its properties. Heating gives the particles more energy, so they move faster, spread further apart, and can break free of one another as a substance melts or boils. The particles never change size, and none are made or lost.

Two ways to run each lesson

Every lesson works as one 60-minute block, or as two 30-minute sessions; the split point is marked in every plan. Look ahead: Lesson 3 needs plastic syringes with caps, Lesson 5 needs honey, cooking oil, dishwashing liquid and 20c coins, Lesson 7 needs a balance that reads to 0.1 g and a fan, Lesson 8 needs small flasks, clear straws, plasticine and balloons, and Lessons 6 and 8 need ice made the day before.

Safety and care in one look

Nothing is tasted in the science room, not even the honey, sugar or salt. Warm water comes from the hot tap, never a kettle; anything boiling is a teacher demonstration. The syringes have no needles, and their caps stay on. Glass thermometers are laid down on the bench. Spills are wiped up at once, and latex allergies are checked before the balloon test.

The term at a glance

One lesson a week for a term. Each lesson stands on the ones before it, so run them in order where you can.

How the sequence builds

Lesson 1 starts from what students can see: the properties of solids, liquids and gases. Lesson 2 builds the model that explains them, and Lessons 3 to 5 test its three parts in turn: the space between particles, their motion and the attraction between them. Lessons 6 and 7 use the model to explain changes of state, Lesson 8 explains expansion, Lesson 9 dissolving, and Lesson 10 brings it together.

Curriculum links (Australian Curriculum V9)

The whole term teaches the Science Understanding descriptor AC9S7U05 quoted on the cover. The lessons also work these Science Inquiry and Human Endeavour descriptors:

Assessment in this pack

• Every plan ends with “Answers and look-fors”: what meeting the idea sounds like in a Year 7 voice, with working.
• The assessment sheet near the front has a class observation checklist and a three-level rubric.
• Lesson 10 is the summative pair: ice in a glass on a hot day, explained with particle pictures, plus the “Show what we know” check.

Materials for the whole term

One gathering session covers all ten lessons. Much of the kit is in a science prep room: syringes, thermometers, beakers, test tubes, balances and droppers. The rest comes from a supermarket trip, and a few things are worth collecting ahead: 20c coins for Lesson 5, empty plastic drink bottles for Lesson 8, and ice made the day before Lessons 4, 6 and 8.

The one-trip list

• From the prep room: 60 mL plastic syringes with caps, thermometers, test tubes, beakers, small flasks, balances reading to 0.1 g, droppers, stirring rods, stopwatches and safety glasses.
• From the classroom: rulers, coloured pencils, scissors, graph paper, pegs, string and paper towel.
• From the supermarket: food colouring, honey, cooking oil, dishwashing liquid, salt, sugar cubes, clear plastic cups, sealable bags, straws and balloons.
• To collect: 20c coins, empty plastic drink bottles, a stick of plasticine, sand, a kitchen sponge, a wooden block, and a fan.

Safety and care in one look

• Nothing is tasted in the science room, not even the honey, the sugar or the salt.
• Warm water comes from the hot tap, never a kettle; anything boiling is a teacher demonstration.
• Syringes have no needles; caps stay on, nozzles point away from faces, and safety glasses go on in Lesson 3.
• Glass thermometers and flasks are laid down on the bench; spills are wiped up at once; check for latex allergies before Lesson 8.

Assessment without extra work

The term assesses itself. Every lesson plan ends with worked answers and look-fors, and Lesson 10 is the summative pair: the ice-in-a-glass task, in which students draw and explain the particles at four moments of a hot afternoon, and the final check. This sheet is the place to note what you see along the way.

The three levels

Class observation checklist

A tick a lesson is plenty; the Lesson 10 task and check fill the gaps.

Word wall cards

Cut out the cards and build the wall as the words arrive: particle, particle model and attraction in Lesson 2; compress and gas pressure in Lesson 3; diffusion in Lesson 4; viscosity and surface tension in Lesson 5; melting point and boiling point in Lesson 6; evaporation and condensation in Lesson 7; expansion in Lesson 8; dissolve and solution in Lesson 9.

Dear families

This term in science, Year 7 studies the particle model: the idea that everything around us is made of tiny particles that never stop moving. Students use it to explain why ice keeps its shape and water does not, why air can be squashed and water cannot, why a smell spreads across a room, why honey pours slowly, why puddles dry up and why bridges have gaps.

Along the way your student will squeeze syringes of air and sand, time food colouring as it spreads through cold and warm water, count how many drops of water fit on a 20c coin, race honey against cooking oil down a tile, graph the temperature of melting ice, build a model thermometer, and weigh salt and water before and after the salt dissolves.

Try this at home

• Put a drop of food colouring into a glass of cold water and a glass of warm water. In which does it spread faster?
• How many drops of water can you fit on a 20c coin before it spills? Try again with a little dishwashing liquid in the water.
• Take a cold drink from the fridge and watch the outside of the can or glass. Where does the water come from?
• With an adult, stretch a balloon over the neck of an empty plastic bottle and stand the bottle in a bowl of hot tap water. What happens, and why?

What to ask your scientist

• Why can you squash air but not water?
• Why does melting ice stay at 0 °C?
• Where does a puddle go when it dries up?
• When salt dissolves in water, where does it go?

A small note on care: students never taste anything in the science room, warm water comes from the hot tap rather than a kettle, and the syringes we use have no needles.

Warm regards,

The Year 7 science team

Printed from the free seegongsik Particle Model of Matter teaching pack · seegongsik.com/au/y7/chemical/AC9S7U05/pack

Solid, liquid or gas?

Matter is anything that has mass and takes up space, and most everyday matter is a solid, a liquid or a gas. Each state has its own properties. A solid keeps its shape and its volume. A liquid keeps its volume but flows to take the shape of its container. A gas has neither a fixed shape nor a fixed volume: it spreads to fill any container and can be squashed into a smaller one. Groups test six samples for these properties, then sort fifteen everyday substances, some of which look as if they belong somewhere else. Lesson 2 builds the model that explains every one of these properties.

We are learning to

• describe the properties of solids, liquids and gases,
• test samples for shape, volume, flow and squashing,
• classify substances by state and give a reason.

Success criteria

• I can name the four properties that tell the three states apart, and test a sample for each.
• I can explain why sand, a sponge and steam belong where they do.

You need

• for each group: six samples, each in a clear sealed container or sealable bag (a wooden block, a kitchen sponge, sand, water, honey and air), and a 60 mL plastic syringe of air with its cap on,
• the worksheet (next sheet), one per student, and the substance cards (third sheet), one set per pair.

Safety: the samples stay sealed, nothing is tasted, and spills are wiped up at once.

Lesson flow (about 60 minutes)

Running two half-sessions instead? Do the odd one out and the four tests in Session A, and the board, the cards and Part C in Session B.

Watch for these ideas

• “Sand is a liquid because it pours.” Each grain is a tiny solid that keeps its own shape; a heap of sand stands up in a pile, which a liquid never does.
• “Gases are not really matter, because we cannot see them.” Air takes up space and pushes back: try squashing the capped syringe.
• “Steam is the white cloud above a kettle.” Steam is invisible; the cloud is tiny drops of liquid water that formed as the steam cooled.

Make it easier, make it bigger

• Easier: sort the cards that are not tricky first, leaving A, B, C, D, E, J until last.
• Bigger: shaving foam, jelly and toothpaste do not fit one pile well. Suggest why.

Answers and look-fors

• Part A, in the order shape, volume, flow, squash: wooden block yes, yes, no, no: a solid; kitchen sponge yes (springs back), yes (the sponge itself), no, yes (air leaves its holes): a solid; sand yes (each grain), yes, yes (grain by grain), hardly: a solid; water no, yes, yes, no: a liquid; honey no, yes, yes (slowly), no: a liquid; air no, no, yes, yes: a gas. The sponge squashes only because air is pushed out of its holes; the sponge itself keeps its shape and springs back.
• Part B: solid B, D, E, I, J, N; liquid A, F, H, L, M; gas C, G, K, O.
• Part C: 1. Each grain of sand is a solid that keeps its own shape and volume; the heap pours only because the grains slide over one another, and it can stand up in a pile. 2. No: steam is an invisible gas, and the white cloud a little above the spout is tiny drops of liquid water that formed as the steam cooled. 3. A gas spreads to fill any container and can be squashed; a liquid keeps its volume and cannot be squashed.
• Bigger: each is a mixture of states. Shaving foam is bubbles of gas in a liquid, jelly is a liquid held in a soft solid network, and toothpaste is fine solid grains in a thick liquid.

Solid, liquid or gas?

A. Four tests

Write yes or no in each box. For the air, push the plunger of the capped syringe to test squashing.

B. Fifteen cards

Write the letter of each card in its column.

C. Questions

Solid, liquid or gas?

Cut out the cards. Lay down the three grey heading cards, read each card, and sort it under its state.

Teacher note: 6 cards are solids, 5 are liquids and 4 are gases.

Particle pictures

Lesson 1 described what solids, liquids and gases do; the particle model explains why. It has four parts: all matter is made of particles far too small to see; the particles are always moving; they attract one another; and between them is empty space, with nothing in it at all. In a solid the particles touch, in fixed rows, and strong attraction holds them so they only vibrate. In a liquid they still touch and attract, but they are jumbled and slide past one another. In a gas they are far apart, with almost no attraction, moving fast in every direction. The class acts out the three states, learns the drawing rules, and finds the mistakes in twelve particle pictures.

We are learning to

• describe the four parts of the particle model,
• draw particle pictures of a solid, a liquid and a gas that follow the rules,
• use the model to explain the properties we tested in Lesson 1.

Success criteria

• My three pictures use the same particles, the same size, touching in the solid and the liquid and far apart in the gas.
• I can find the mistake in a particle picture and say how to fix it.

You need

• an open space, such as the yard or the hall, for the act-out,
• the worksheet (next sheet), one per student, the picture cards (third sheet), one set per pair, and coloured pencils.

Safety: in the act-out students walk, never run, and touch only when they link arms.

Lesson flow (about 60 minutes)

Running two half-sessions instead? Do the act-out, the board and the drawing rules in Session A, and the cards and Part C in Session B.

Watch for these ideas

• “The particles of a gas are bigger.” Particles keep their size in every state; only the spacing changes.
• “There is air between the particles.” Between particles there is nothing at all. Air is itself made of particles.
• “A particle of ice is cold and hard.” Hardness, colour and coldness belong to the whole substance, not to its single particles.

Make it easier, make it bigger

• Easier: start with the cards that show one container, and leave the two before-and-after cards, D and H, until last.
• Bigger: our act-out and our pictures are both models. Name three ways in which they are not like real particles.

Answers and look-fors

• Part A: solid: touching, in fixed rows; vibrate on the spot; attraction strong: holds each particle in its place. liquid: touching, but jumbled; slide past one another; attraction still strong enough to keep them together. gas: far apart, spread through the container; fast, in straight lines in every direction; attraction almost none.
• Part B: drawn right, C, E, F, I, J. Mistakes: A, the particles of a solid touch, with no wide gaps between them; B, a gas spreads through the whole jar, not just the top of it; D, no particles are lost when ice melts, so the water needs the same twelve; G, the particles of a liquid are jumbled, not lined up in rows like a solid; H, the particles do not grow; in steam they are the same size, only far apart; K, the particles of a liquid touch; they are jumbled, not spread out; L, gas particles are far apart and spread through the jar, not clumped in a corner.
• Part C: 1. In a solid, strong attraction holds the particles in fixed places, so the solid keeps its shape; in a liquid the particles can slide past one another, so it flows to fit its container. 2. In a gas there is empty space between the particles, so they can be pushed closer together; in a liquid they already touch. 3. They are the same particles, the same size and the same number; only their arrangement, their motion and how strongly they hold together differ.
• Bigger: real particles are far smaller and far more numerous, they move in three dimensions and much faster, they do not choose where to go, and they are not round dots or people.

Particle pictures

A. The same twelve particles, three ways

Draw twelve particles, all the same size, in each box. Then fill the table.

B. Spot the mistake

For four of the cards with a mistake, write what is wrong and how to fix it.

C. Questions

Drawn right, or a mistake?

Cut out the cards. Lay down the two grey heading cards, check each picture against the rules, and sort it.

Teacher note: 5 pictures are drawn right and 7 have a mistake.

Squeeze it

A gas can be squashed into a smaller space, but a liquid or a solid hardly at all. The particle model explains why: in a gas there is a lot of empty space between the particles, so they can be pushed closer together, while in a liquid or a solid the particles already touch. Squashing a gas also makes it push back harder. Its particles now strike the walls of the container more often, and that push of countless particles on the walls is gas pressure. Groups squeeze sealed syringes of air, water, dry sand and wet sand, and explain what they find.

We are learning to

• compare how easily a solid, a liquid and a gas can be compressed,
• explain compressing with the space between particles,
• explain gas pressure with particles striking the walls of their container.

Success criteria

• I can explain, with particle pictures, why the air squashed and the water did not.
• I can explain why the plunger slid back out when I let go.

You need

• for each group: four 60 mL plastic syringes with caps and no needles, filled to the 50 mL mark with air, water, dry sand and wet sand (see the station sheet for how), safety glasses and paper towel,
• the worksheet (next sheet), one per student, and the station sheet (third sheet), cut into four cards.

Safety: safety glasses on, nozzles pointed at the bench, and caps checked before every push.

Lesson flow (about 60 minutes)

Running two half-sessions instead? Do the push back and the four stations in Session A, and the board, the pictures and Part C in Session B.

Watch for these ideas

• “The air squashed because its particles got smaller.” The particles keep their size; only the spaces between them shrink.
• “The sand squashed, so solids can be squashed.” Each grain is a solid and does not squash; the grains settled into the air gaps between them. With water in the gaps, the sand did not move at all.
• “Pressure is something stored inside the syringe.” Pressure is the push of countless particles striking the walls and the plunger.

Make it easier, make it bigger

• Easier: run only the air and the water stations, and draw only those two in Part B.
• Bigger: the example air syringe went from 50 mL to about 25 mL. About how many times as often were its particles striking the plunger at the end? Explain.

Answers and look-fors

• Part A, example class averages: air 25 mL, 25 mL smaller, slid back out to 50; water 50 mL, no change, stayed at 50; dry sand 47.7 mL, 2.3 mL smaller, stayed where it was pushed; wet sand, with water filling the gaps 50 mL, no change, stayed at 50.
• Part B: the air before is particles far apart filling the syringe, and after is the same particles, the same size, closer together in half the space. The water is particles touching, the same before and after.
• Part C: 1. In air the particles are far apart with empty space between, so they can be pushed closer together; in water they already touch, so there is no space to squash out. 2. In less space the air particles struck the plunger more often, so the air inside pushed harder than the air outside; when we let go, the plunger was pushed out until the two pushes balanced. 3. The sand grains do not squash, but there is air between them, and the push let the grains settle a little closer into those gaps. In the wet sand, water fills the gaps, and water cannot be squashed.
• Bigger: about twice as often, because the same particles, moving just as fast, were packed into half the space.

Squeeze it

A. Four syringes

Each syringe starts at 50 mL. Record the smallest volume each person could push it to.

B. Before and after the push

Draw the particles in the air and in the water, before the push and at the smallest volume.

C. Questions

Four syringe stations

Getting ready (teacher): for air, pull the plunger to 50 mL and cap the nozzle. For water, draw it up past 50 mL, hold the nozzle up, push out every bubble, then cap. For sand, take the plunger out, pour sand to the 50 mL mark and tap it level, push the plunger in until it touches the sand, then cap. For wet sand, do the same but pour in water to cover the sand before the plunger goes in, and let the extra water out through the nozzle before you cap it.

Teacher note: between classes, take the plunger out of the dry sand syringe, loosen the sand and fill it to the 50 mL mark again; the pushed grains have settled lower.

Particles on the move

The particles of liquids and gases never stop moving. They wander in every direction, bumping into one another, so particles that start crowded in one place spread out until they are mixed evenly. This spreading is diffusion, and it is why a smell crosses a room and a drop of food colouring spreads through still water. The warmer the substance, the faster its particles move, and the faster diffusion happens. Groups time food colouring spreading through cold, room-temperature and warm water, graph their results, and read how a jiggling speck under a microscope convinced scientists that particles are real.

We are learning to

• describe diffusion and explain it with moving particles,
• test how temperature changes the speed of diffusion, keeping everything else the same,
• explain how new evidence changed what scientists thought about particles.

Success criteria

• I can use the particle model to explain why the colour spread fastest in the warm water.
• I can name the variable we changed, the one we measured and two we kept the same.

You need

• for each group: three clear plastic cups standing on white paper, 250 mL each of water from the fridge, the cold tap and the hot tap, food colouring with a dropper, a thermometer and a stopwatch; an orange for the opening,
• the worksheet (next sheet), one per student, and the exit tickets (third sheet), cut into four.

Safety: warm water comes from the hot tap, never a kettle. Food colouring stains clothes and skin.

Lesson flow (about 60 minutes)

Running two half-sessions instead? Do the smell and the three cups in Session A, and the board, the graph, the reading and the ticket in Session B.

Watch for these ideas

• “The colour disappeared.” Every colour particle is still there, spread so thinly that the water looks paler.
• “Diffusion stops once the colour is even.” The particles keep moving; there is simply no more change we can see.
• “It was all the heat.” Warm water can also carry small currents that mix the colour. Leaving the cups still for a minute and adding the drop gently keeps the test fair.

Make it easier, make it bigger

• Easier: run only the cold and the warm cups.
• Bigger: use the graph to predict the time for water at 35 °C, then test it.

Answers and look-fors

• Part A, example class averages: cold, from the fridge (8 °C) 7.5 min; room temperature (22 °C) 4.5 min; warm, from the hot tap (45 °C) 2 min.
• Part B: the warmer the water, the shorter the time; it falls steeply from the cold to the room-temperature cup, then more gently. Changed: the temperature of the water; measured: the time for the colour to spread; kept the same: the cup, the amount of water, one drop, how gently it went in, no stirring.
• Part C: 1. Tiny specks jiggling in water without ever stopping; specks of dust did it too, so it was not life, and nobody could see what was pushing them. 2. Einstein worked out how far a speck should wander if moving water particles were bumping it, and Perrin’s careful measurements matched; this new evidence convinced most scientists that particles are real.
• Exit ticket: 1. The spreading of particles from where they are crowded to where they are fewer, because they keep moving. 2. In warm water the particles move faster, so the colour particles are bumped along and spread out sooner. 3. On a warm day the particles in the air move faster, so the smell spreads sooner.
• Bigger: between 4.5 and 2 min, nearer 2; a sensible prediction is about 3 min. Cold water took 3.8 times as long as warm water.

Particles on the move

A. Three cups

B. Graph the averages

C. A jiggling clue

In 1827 the botanist Robert Brown, who had earlier collected thousands of plants on Matthew Flinders’ voyage around Australia, looked through a microscope at tiny specks from pollen grains floating in water. The specks jiggled about and never stopped. Specks of dust did the same, so it was not life, and for almost eighty years nobody could explain it. Around 1900 many scientists still doubted that particles were real. In 1905 Albert Einstein worked out that the specks would jiggle like this if the moving particles of the water, far too small to see, were bumping them unevenly, and predicted how far a speck should wander. In 1908 Jean Perrin measured the wandering carefully, and it matched.

Exit tickets

Cut into four. Students answer on their own.

Teacher note: the answers are on this lesson’s plan.

Particles that hold on

Particles attract one another, and that pull is what holds a solid or a liquid together. Its strength shows up in everyday properties. At the surface of a liquid, each particle is pulled sideways and inwards by its neighbours but not outwards, so the surface behaves like a stretched skin. This is surface tension, and it lets water pile up into a dome on a coin. In a thick liquid such as honey, the particles hold on to one another more strongly as they slide past, so it flows slowly: it has a high viscosity. Groups count how many drops fit on a 20c coin, with and without soap, and race four liquids down a tilted tile.

We are learning to

• describe surface tension and viscosity,
• explain both with the attraction between particles,
• time a race fairly, repeat it and average the results.

Success criteria

• I can explain why water piles up on a coin, and why soap lets fewer drops fit.
• I can rank four liquids by viscosity from our results, and explain the order with attraction.

You need

• for each group: a 20c coin on a paper towel, a dropper, a cup of water and a cup of water with a squirt of dishwashing liquid; a teaspoon each of water, cooking oil, dishwashing liquid and honey; a smooth tile or tray propped on two books, a ruler, a marker and a stopwatch,
• the worksheet (next sheet), one per student, and the exit tickets (third sheet), cut into four.

Safety: wipe up spills at once, because oil, honey and soapy water make the floor slippery. Nothing is tasted.

Lesson flow (about 60 minutes)

Running two half-sessions instead? Do the drops on a coin and the board in Session A, and the race, Part C and the ticket in Session B.

Watch for these ideas

• “The coin holds the water on.” The water particles hold on to one another; the dome stays whole until it grows too heavy for that pull.
• “Honey is slow because it is heavy.” A spoonful of dishwashing liquid weighs about the same as a spoonful of water, yet it is far slower. What slows a liquid is how strongly its particles hold on as they slide past one another.
• “Soap makes the water lighter.” Soap weakens the pull between the water particles at the surface, so the skin breaks sooner.

Make it easier, make it bigger

• Easier: race two liquids only, water and honey.
• Bigger: stand the honey in a cup of hot tap water for five minutes and race it again. Predict first, then explain the result with particles.

Answers and look-fors

• Part A, example class averages: water 30 drops, soapy water 11 drops.
• Part B, example class averages: water 1 s, cooking oil 3.9 s, dishwashing liquid 12 s, honey 76 s. From runniest to thickest: water, cooking oil, dishwashing liquid, honey.
• Part C: 1. Each water particle at the surface is pulled sideways and inwards by its neighbours, which holds the surface together like a skin, so the water piles up into a dome until it is too heavy. 2. Honey: it took longest, about 76 s, so its particles hold on to one another most strongly as they slide past. 3. Weight is not what slows it: its particles hold on to one another more strongly than water’s as they slide past, so it has a higher viscosity.
• Exit ticket: 1. The pull between the particles at the surface of a liquid, which makes the surface act like a skin. 2. Soap weakens the pull between the water particles at the surface, so the dome breaks sooner. 3. Water, cooking oil, honey.
• Bigger: the example class’s warmed honey took about 32 s instead of 76 s. Warming gives the particles more energy, so they pull away from one another and slide past more easily.

Particles that hold on

A. Drops on a coin

B. Liquid race

Time each liquid from the start line to the finish line, 20 cm down the tilted tile.

C. Questions

Exit tickets

Cut into four. Students answer on their own.

Teacher note: the answers are on this lesson’s plan.

Melting and freezing

When a solid is heated, its particles vibrate faster and faster until they can break out of their fixed places: the solid melts. A pure substance melts at one temperature, its melting point, and the temperature stays there until the last of the solid has gone, because the energy going in is used to free particles from their places rather than to make them move faster. Cooling runs the other way, and a liquid freezes at the same temperature. The stronger the attraction between the particles, the higher the melting and boiling points. Groups warm crushed ice in a water bath, graph its temperature, then use melting and boiling points to sort twelve substances by their state in the classroom.

We are learning to

• describe melting and freezing with the particle model,
• graph temperature against time and explain the flat part,
• use melting and boiling points to predict the state of a substance.

Success criteria

• I can explain why the temperature stayed at 0 °C while the ice melted.
• I can use a melting point and a boiling point to say whether a substance is a solid, a liquid or a gas at 22 °C.

You need

• for each group: a test tube a third full of crushed ice from the freezer, a beaker of warm tap water to stand it in, a thermometer, a stirring rod and a stopwatch,
• the worksheet (next sheet), one per student, and the point cards (third sheet), one set per pair.

Safety: stir the ice with the rod, not the thermometer, and lay thermometers down on the bench. Warm water comes from the hot tap.

Lesson flow (about 60 minutes)

Running two half-sessions instead? Do the prediction, the warming ice and the graph in Session A, and the board and the cards in Session B.

Watch for these ideas

• “The temperature keeps rising while ice melts.” Our graphs show a flat part: the energy frees particles from their places instead of speeding them up.
• “Melting and dissolving are the same thing.” Melting is one substance turning from solid to liquid as it is heated; dissolving is one substance spreading through another, which comes in Lesson 9.
• “Freezing means adding cold.” Freezing happens as energy is taken away: the particles slow down until the attraction holds them in fixed places.

Make it easier, make it bigger

• Easier: read the thermometer every two minutes instead of every minute.
• Bigger: on a −40 °C day in Antarctica, which of the liquid cards would be frozen? Why do thermometers for very cold places hold coloured ethanol rather than mercury?

Answers and look-fors

• Part A, example class readings: −6 °C, −3 °C, −1 °C, 0 °C, 0 °C, 0 °C, 0 °C, 0 °C, 0 °C, 1 °C, 4 °C, 8 °C, 12 °C, 15 °C, 18 °C, one a minute. The ice melted from about minute 3 to minute 8, while the reading stayed at 0 °C.
• Part B: the line rises to 0 °C, stays flat while the ice melts, then rises again. 1. 0 °C. 2. The energy from the warm water went into freeing the particles from their fixed places, not into making them move faster, so the temperature stayed the same until all the ice had melted. 3. At 0 °C, the same temperature.
• Part C: solid at 22 °C, B iron, D zinc, E sulfur, I copper, K iodine; liquid, C water, F mercury, G ethanol, J acetone; gas, A oxygen, H nitrogen, L chlorine. The highest melting point is iron’s, 1538 °C: of the twelve, its particles hold on to their places most strongly.
• Bigger: water (melts at 0 °C) and mercury (melts at −39 °C) would be frozen; ethanol and acetone would still be liquid, and chlorine, which boils at −34 °C, would have condensed to a liquid. Ethanol stays liquid down to −114 °C, so it still works in extreme cold, but mercury freezes at −39 °C.

Melting and freezing

A. Warming ice

B. Graph the readings

C. Twelve substances at 22 °C

Solid, liquid or gas at 22 °C?

Cut out the cards. Lay down the three grey heading cards, then use each card’s melting and boiling points to sort it by its state in our classroom, at 22 °C.

Teacher note: 5 cards are solids at 22 °C, 4 are liquids and 3 are gases. Melting and boiling points are at normal air pressure.

Evaporating, boiling, condensing

A liquid can turn into a gas in two ways. Evaporation happens at the surface, at any temperature: the particles in a liquid move at a range of speeds, and the fastest ones near the surface break away from the pull of their neighbours. It goes faster when the liquid is warmer, when more of it is open to the air, and when a breeze carries the escaped particles away. Boiling happens at one temperature, the boiling point, with bubbles of gas forming all through the liquid. Condensation is the reverse: gas particles that meet a cold surface slow down, and the attraction pulls them back together into a liquid. Groups weigh drying paper towels in a fair test, then sort twelve everyday changes.

We are learning to

• describe evaporation, boiling and condensation with the particle model,
• run a fair test with a control, measuring mass over time,
• explain what makes evaporation faster.

Success criteria

• I can explain, with particles, why the towel in front of the fan dried fastest.
• I can tell evaporating, boiling and condensing apart in everyday examples.

You need

• for each group: four squares of paper towel (10 cm by 10 cm), a dropper, a balance reading to 0.1 g, pegs and string; a fan and a sunny spot for the class; a kettle for the teacher,
• the worksheet (next sheet), one per student, and the change cards (third sheet), one set per pair.

Safety: the kettle is a teacher demonstration, well back from the bench edge; keep the fan’s cord away from water.

Lesson flow (about 60 minutes)

Running two half-sessions instead? Do the towels, the board and the cards in Session A, and the graph and the questions in Session B.

Watch for these ideas

• “Water disappears when it evaporates.” Its particles are still there, spread through the air as an invisible gas, water vapour.
• “The water on a cold can leaked through the metal.” A sealed can cannot leak; the drops come from water vapour in the air, condensing on the cold surface.
• “The bubbles in boiling water are air.” They are water vapour, formed inside the liquid.

Make it easier, make it bigger

• Easier: compare two towels only, the control and the one in front of the fan.
• Bigger: high on a mountain, water boils at about 90 °C. Why does pasta take longer to cook there?

Answers and look-fors

• Part A, example class results (water left after 30 minutes): flat, in still air in the shade 0.8 g; flat, in front of a fan 0 g; flat, in the sun 0 g; folded in four, in still air in the shade 1.4 g.
• Part B: every line falls; in the first 15 minutes the towels lost 1.4 g (flat, in front of a fan), 1.2 g (flat, in the sun), 0.6 g (flat, in still air in the shade), 0.3 g (folded in four, in still air in the shade). 1. flat, in front of a fan: moving air; flat, in the sun: warmth; folded in four, in still air in the shade: less surface; everything else, the towel, the 2.0 g of water and the balance, stayed the same. 2. The one in front of the fan: water particles escape from the surface at any temperature, and the moving air carried them away, so fewer wandered back into the towel. 3. Folded, less of the towel was open to the air, so fewer particles were at the surface ready to escape.
• Part C: evaporating B, D, E, I, J; condensing A, F, H, L; boiling C, G, K.
• Kettle: the gap holds steam, an invisible gas; a little further out it cools and condenses into the tiny drops of the white cloud.
• Bigger: once the water boils it cannot get any hotter, so up there the pasta sits in water at about 90 °C instead of 100 °C and cooks more slowly.

Evaporating, boiling, condensing

A. Drying towels: water left (g)

B. Graph the water left

C. Twelve changes

Evaporating, condensing or boiling?

Cut out the cards. Lay down the three grey heading cards, read each card, and sort it under the change it shows.

Teacher note: 5 cards show evaporating, 4 condensing and 3 boiling.

Hot and cold: expansion

Most substances take up more space as they warm and less as they cool. The particle model explains why: heated particles move more, so they push one another further apart, while the particles themselves stay the same size. Solids expand the least, because strong attraction holds their particles close; liquids expand more; gases expand by far the most, because almost nothing holds their particles together. Expansion is useful in thermometers and a nuisance in bridges, railway lines and power lines, which are built with room to grow on hot days. Groups build a model thermometer and a balloon-topped bottle, then judge twelve statements.

We are learning to

• describe expansion and contraction with the particle model,
• compare how much solids, liquids and gases expand,
• spot and correct misconceptions about particles.

Success criteria

• I can explain why the water rose up the straw without saying that the particles grew.
• I can explain why bridges have small gaps at their joins.

You need

• for each group: a 100 mL flask or small glass bottle filled to the brim with coloured water, a clear straw, a lump of plasticine, a ruler, three tubs of water (iced, cold tap and hot tap), an empty plastic drink bottle and a balloon,
• the worksheet (next sheet), one per student, the statement cards (third sheet), one set per pair, and a ball and ring, if you have one.

Safety: warm water comes from the hot tap; check for latex allergies before handing out balloons; carry flasks with two hands.

Lesson flow (about 60 minutes)

Running two half-sessions instead? Do the stuck lid, the model thermometer and the balloon bottle in Session A, and the board, the statements and the questions in Session B.

Watch for these ideas

• “The particles get bigger when they are heated.” They stay the same size; they move more and spread further apart.
• “The level dipped first, so the water shrank.” The glass warmed first and expanded, giving the water a moment of extra room; then the water warmed and expanded more.
• “Cold particles shrink, so the balloon was sucked in.” The cooler air particles move more slowly and hit the balloon less hard and less often, so the air outside pushes it in.

Make it easier, make it bigger

• Easier: use the room-temperature mark and the warm tub only.
• Bigger: in the example class the water rose 0.9 cm from the iced tub to room temperature, but 3.6 cm from room temperature to the warm tub. Is the model thermometer’s scale even? Why do real thermometers hold coloured ethanol instead of water?

Answers and look-fors

• Part A, example class averages: iced water (5 °C) 3.1 cm; room temperature (22 °C) 4.0 cm; warm, from the hot tap (45 °C) 7.6 cm. In the warm tub the level dips for a moment before it rises.
• Part B: in the hot tub the balloon stood up and filled a little; in the iced tub it was pulled into the neck. Both pictures have the same number of air particles, moving fast in the hot bottle and slowly in the cold one.
• Part C: particle model, C, D, G, H, J. Misconceptions: A, the particles stay the same size; they vibrate more and push further apart; B, heat is energy, not a substance; it makes the particles move more; E, no particles are made; the same particles take up more space; F, the particles keep their size; the slower air particles hit the balloon less often and less hard, so the air outside pushes it in; I, the spaces between particles hold nothing at all; air is made of particles too; K, they still vibrate, only less; L, the same air is inside, so the mass stays the same.
• Questions: 1. As the water warmed, its particles moved more and pushed one another a little further apart, so the same particles took up more space, and the only way out was up the straw. 2. On a hot day the steel expands; the gaps give it room, so the bridge or rail does not buckle. 3. The air in the bottle: a gas expands far more than a liquid or a solid, because almost nothing holds its particles together.
• Bigger: no; per degree the water rose about 3 times as far above room temperature as below it, because water expands more for each degree the warmer it gets. Ethanol expands far more evenly and stays liquid far below 0 °C.

Hot and cold: expansion

A. Model thermometer

B. Balloon bottle

Draw the air particles inside the bottle and the balloon, with an arrow on each to show how fast it moves.

C. Twelve statements

Choose two misconceptions and rewrite each one so that it fits the particle model.

D. Questions

Particle model, or misconception?

Cut out the cards. Lay down the two grey heading cards, read each statement, and sort it. Be ready to fix each misconception.

Teacher note: 5 statements fit the particle model and 7 are misconceptions.

Dissolving

When salt or sugar dissolves in water it seems to disappear, but every one of its particles is still there. The moving water particles knock solute particles off the surface of the crystal, and they spread out between the water particles until they are mixed evenly through the liquid: a solution. The particles are far too small to see, so the solution is clear, but nothing has been made or destroyed, and the solution weighs exactly as much as the water and the solute did. Dissolving is faster in warmer water, whose particles move faster, and when the water is stirred, which carries dissolved particles away from the crystal and brings fresh water to it. Groups weigh salt and water before and after dissolving, then time sugar cubes in a fair test.

We are learning to

• explain dissolving with the particle model,
• show that mass is conserved when a substance dissolves,
• test how temperature and stirring change the speed of dissolving.

Success criteria

• I can explain where the salt went, and why the mass did not change.
• I can explain why warm, stirred water dissolves a sugar cube fastest.

You need

• for each group: a balance, a beaker holding 100 mL of water, 10 g of salt in a paper cup and a stirring rod; four sugar cubes, four cups (two of water from the fridge, two from the hot tap, 200 mL in each) and a stopwatch,
• the worksheet (next sheet), one per student, and the exit tickets (third sheet), cut into four.

Safety: nothing is tasted, not even the sugar water. Warm water comes from the hot tap.

Lesson flow (about 60 minutes)

Running two half-sessions instead? Do the sugar glass, the weighing and the board in Session A, and the sugar cubes, Part C and the ticket in Session B.

Watch for these ideas

• “The salt melted.” Melting needs heating and turns one substance into its own liquid; here the salt particles spread out between the water particles at room temperature.
• “The sugar disappeared, so its mass is gone.” All of its particles are still there, and the balance shows it.
• “Group 2 lost 0.1 g, so some salt was destroyed.” A few grains left in the cup or a tiny splash explains a difference that small; the other groups found none.

Make it easier, make it bigger

• Easier: time two cups only, cold and still against warm and stirred.
• Bigger: how could you get the salt back out of the solution? Predict the mass you would recover, and why it might be a little less.

Answers and look-fors

• Part A, example class: Group 1 186.5 and 186.5 g; Group 2 192.0 and 191.9 g; Group 3 178.3 and 178.3 g. Group 2’s 0.1 g is about what a few grains left in the cup would weigh, and the other groups found no change at all. The mass does not change, because every salt particle is still there.
• Part B, example class averages: cold, still 9 min; cold, stirred 2 min; warm, still 4 min; warm, stirred 0.7 min. From fastest to slowest: warm, stirred; cold, stirred; warm, still; cold, still. Fair tests of stirring: cold still against cold stirred, or warm still against warm stirred. Fair tests of temperature: cold still against warm still, or cold stirred against warm stirred.
• Part C: 1. The moving water particles knocked salt particles off the crystals, and they spread out between the water particles until they were mixed evenly, too small and too spread out to see. 2. No particles were made or destroyed, so the total mass stayed the same. 3. In warm water the particles move faster and strike the cube harder and more often; stirring carries the dissolved sugar away from the cube and brings fresh water to it.
• Exit ticket: 1. 154 g. 2. Use warmer water, stir it, or crush the cube first. 3. Its particles spread out evenly between the water particles.
• Bigger: leave the solution in a shallow dish in a warm, sunny spot until the water has evaporated: about 10 g of salt is left, a little less if some sticks to the beaker or is lost moving it.

Dissolving

A. Weigh it

Put the beaker of water and the paper cup of salt on the balance together. Tip the salt in and stir until it has all dissolved, then put the empty cup back on the balance.

B. Sugar cubes

C. Questions

Exit tickets

Cut into four. Students answer on their own.

Teacher note: the answers are on this lesson’s plan.

Show what we know

The last lesson brings the term together. Students follow the water from an ice cube through a hot afternoon, from the freezer to a splash drying on the table, with a particle picture and a particle explanation at each of four moments. Then each student sits the final check on their own, and the class finishes with the unit quiz on the board.

We are learning to

• use the particle model to explain changes of state in a new situation,
• draw particle pictures that follow the rules of the model,
• show what we know about particles on our own.

Success criteria

• My four particle pictures follow the rules, and each change is named and explained with the arrangement, motion, attraction or energy of the particles.
• I can back each answer on the final check with a particle explanation or a reason.

You need

• the ice-in-a-glass task (next sheet) and the final check (third sheet), one each per student,
• the interactive unit open for the closing quiz.

Lesson flow (about 60 minutes)

Running two half-sessions instead? Do the task and the partner check in Session A, and the final check and the class quiz in Session B.

Watch for these ideas

• “The ice particles melt.” The particles stay just as they were; only their arrangement and motion change.
• “The drops on the glass leaked through it.” Ask: could water get through glass? Where else could it come from?
• Pictures with fewer or bigger particles after a change. Ask: were any particles made or lost? Did any of them grow?

Make it easier, make it bigger

• Easier: draw the first picture together on the board, and let students draw the other three.
• Bigger: the drink stays at about 0 °C for as long as there is still ice in it. Explain why.

Answers and marking guide

• Task: in the freezer, no change: a solid: the particles touch in fixed rows and only vibrate, held in place by strong attraction; in the drink, melting: energy from the warmer drink makes the particles at the edge of each cube vibrate harder until they break free of their places and slide away as liquid water; on the glass, condensing: water vapour particles in the air strike the cold glass, lose energy and slow down, and the attraction pulls them together into drops; on the table, evaporating: the fastest water particles at the surface of the splash escape into the air as water vapour, sooner in the warm afternoon air. Last question: moment 3; the water vapour particles gave energy to the cold glass, which warmed a little, and slowed down until the attraction held them together.
• Check: 1. liquid. 2. In air the particles are far apart with empty space between them, so they can be pushed closer together; in water the particles already touch, so there is no space to squash out. 3. warm water. 4. While the ice melts, the energy goes into freeing particles from their fixed places, not into making them move faster, so the temperature stays at 0 °C until all the ice has melted.
• Check: 5. gas, because 22 °C is above its boiling point. 6. The wind carries away the water particles that escape from the washing, so fewer wander back, and more escape each minute. 7. Heating makes the particles of the metal lid vibrate more and push further apart, so the lid expands; metal expands more than glass, so the lid loosens. 8. 205 g; the sugar particles spread out evenly between the water particles, and none were destroyed.
• Bigger: the energy from the drink goes into melting the ice, freeing its particles from their places, so while any ice is left the drink cannot warm above its melting point.
• Scoring: 1 mark each for 1, 3 and 5; 2 marks each for 2, 4, 6, 7 and 8. The rubric near the front of the pack turns the task and the check into a level.

Ice in a glass on a hot afternoon

For each moment, draw the water particles, name the change (or write “no change”), and explain it with particles.

Show what we know

Show what you know about the particle model. Read each item, then circle or write.

Teacher note: the marking guide is on this lesson’s plan; the rubric near the front of the pack turns the score into a level.