Matter as Particles - Science Notes PDF

Matter as Particles Flipped classroom...

Matter as Particles Flipped classroom e-aristo.hk/r/ isfcu6.e fc06 In this Unit, we will learn about: particle theory Learning Science in English (U6: Describing arrangements and movements of particles) the particle model for the three states of matter Foundation Worksheets (U6) dissolving thermal expansion and contraction Quick Revision Notes (U6) gas pressure density Answers to Textbooks (U6) Teaching PowerPoint (U6, by sections) e-Companion (e-Book)  n, in k th is be au tif ul ite m is only a decoratio You may th th er mometer called th an th at. It is a but it does more eter. the Galileo Thermom Ga lil eo Th er mo me te r glass bulb A Galileo Thermometer is basically a glass tube containing a liquid and some glass bulbs. When the temperature changes, some bulbs will float and some will sink in the liquid. We can know the temperature from the floating and sinking of these glass tube bulbs. containing a liquid A Galileo Thermometer works on the principle that density changes with temperature. In this Unit, you will learn that matter is made up of particles. From this, you can understand more about the properties of matter, for example, thermal expansion and contraction, and density. Teaching notes How a Galileo thermometer works: (a) The glass bulbs have the same density. The tags have slightly different masses. A tag representing a higher temperature has a lower mass. (b) Thus, after the tags are attached to the bulbs, the overall density of each tag-and-bulb differs slightly from the others. The one for a higher temperature has a lower overall density. (c) When the temperature changes, the density of the liquid inside the glass tube varies but the densities of the bulbs are almost the same. The bulbs will float or sink accordingly. (d) The temperature can be read from the lowest floating bulb, i.e. the 'red' bulb on the left photo. 1. When temperature 1. When temperature changes, what happens to the particles of increases, particles will a substance? What happens to the size of the substance?move faster and become further apart. The size of the substance 2. What is density? How is density related to floating and sinking of will increase. a substance in a liquid? 2. Density is the mass per unit volume of a substance. A substance with a lower density floats in a liquid 3. How does the density of a substance change with a higher density. with temperature? 3. The density of a substance decreases when its temperature increases. thermal expansion and contraction 熱脹冷縮 142  6 Matter as Particles Particle theory Misconception Students may think that air is Section objective not matter as it cannot be seen with the naked eye. A What is matter? Students should realize the two properties of matter. Emphasize that air is matter. It has mass and takes up Matter is around us. This book, your shirt and your body are matter. space. The set-up below can The water you drink and the air you breathe are also matter. All show that air takes up space: matter has two properties: it has mass and it takes up space. paper towel water empty glass However, there are things which are not matter, for example light. These things do not have mass and do not take up space. Activity 6.1 Is this matter? 1. Look at the picture below. Which of the following are matter? Put a ‘ ’ in the box if it is matter. cloud tree sound Teaching notes Smoke consists of ash, water drops, etc. It is smoke matter. water heat 2. What do the things you chose above have in common? They have mass and take up space. matter 物質 mass 質量 space 空間 143 6 Matter as Particles Matter is anything that has mass and takes up space. Section objectives Students should be able to B Basic ideas of the particle theory state that all matter is made up of particles. Have you ever thought about what matter is made up of? In fact, recognize that particles are in random motion. people had already begun to think about this question thousands of years ago. Over the years, many scientists have done investigations and experiments to find the answer. In our history, the following three people have made important contributions: Democritus (A Greek thinker 460 – 370 B.C.) Robert Brown (A scientist in the 19th century) Albert Einstein (A scientist in the 20th century) Learn more a John Dalton b c Besides Democritus, Brown and Einstein, many scientists also made contributions to our understanding of what matter is made up of. John Dalton (1766–1844) was one of them. Search the Internet to learn more about Dalton’s contribution. Fig. 6.1 (a) Democritus, (b) Robert Brown and (c) Albert Einstein Teaching notes Let us now turn to the next page and see what these people Dalton performed many experiments and worked out have done. the relative atomic weights of some elements such as nitrogen and oxygen, relative to that of hydrogen. His ideas about matter are summarized in Dalton's atomic theory. 144 Democritus’s idea very tiny pieces that break break break cannot be further divided Teaching notes Remind students Democritus suggested that if matter was divided that Democritus’ idea can also be into smaller and smaller pieces, at some point, applied to liquids and gases, which we would get very tiny pieces that could not be is not trivial for students. further divided. These tiny pieces are called Democritus particles. Particles are the building blocks of matter. However, Democritus’s idea of particles was not accepted in his time as there was no evidence to support it. 400 B.C. 1827 Robert Brown’s discovery pollen grain In an experiment, Brown noticed that pollen water grains appeared to be moving randomly on their own in still water. Brown did not know what caused the pollen grains to move. He also did not know that his discovery would turn out to be evidence to support the idea of particles. The motion of the pollen grains was later called Brownian motion. Brown particle 粒子 Brownian motion 布朗運動  6 Albert Einstein's explanation Matter as Particles Einstein explained Brownian motion of the pollen grains in water as follows. Water is made up of very small water particles. The water particles are much smaller than the pollen grains and they are moving in different directions. They hit the pollen grains in different directions from time to time. Therefore, the pollen grains are moving randomly in zigzag paths. pollen grain water particle Albert Einstein Fig. 6.2 Brownian motion of pollen grains in water is caused by the water particles pushing the pollen grains in different directions. 1905 Now zigzag path 鋸齒形路徑 146  6 SPS: OB Matter as Particles Experiment 6.1 Demonstration e-aristo.hk/r/ Experiment video isexptu6i01.e ev06s1 Observing Brownian motion under a microscope Experiment preparation To prepare a slide of diluted milk: Material and apparatus 1. Add a small drop of water to a slide with a dropper. microscope 1 video imaging device and a projector 1 set 2. Dip the point of a pin into milk, then into the water droplet, and slide 1 kinetic motion model 1 stir slightly. cover slip 1 diluted milk 3. Place a cover slip over the drop of diluted milk. Apply vaseline on all four edges of Procedure the cover slip on the slide. This can seal the diluted milk to reduce its Part A: Observing a drop of diluted milk rate of evaporation. 1. Your teacher will prepare a slide of diluted milk and put it on the stage of a microscope. The diluted milk is composed of fat droplets suspended in water. 2. Adjust the focus of the microscope until you can see tiny ‘bubbles’ on the screen. These tiny ‘bubbles’ are fat droplets. fat droplet 3. Look at one of the fat droplets carefully. What do you observe? The fat droplet moves randomly (does not move/moves randomly). Part B: Using the kinetic motion model to understand the observation above 4. (a) Your teacher will show you a kinetic motion model. A ball and some small beads are placed inside the model. (b) Turn on the model. Observe carefully the movement of the ball and what causes the ball to have this movement. ball small beads lif tp Cont'd ag kinetic motion model 粒子運動模擬器 e 147 6 Matter as Particles Discussion 1. Compare the kinetic motion model with the diluted milk in Part A. What do the ball and small beads in the model represent? The ball represents the fat droplet (water particle/fat droplet). The small beads represent the water particles (water particles/fat droplets). 2. From the observation of the ball in the kinetic motion model, explain the movement of the fat droplet in the diluted milk in Part A. There are a lot of water particles in the diluted milk and they are much smaller than the fat droplet. They are moving in different directions (moving in different directions/at rest). They hit the fat droplet from different directions. This causes the fat droplet to move randomly. Besides Brownian motion, scientists have done many experiments and found a lot of evidence to support the idea of particles. They have summarized the idea into the particle theory. The main points of the particle theory are as follows: All matter is made Particles are up of particles. very small. There are empty Different matter is spaces between Particle made up of particles. theory different particles. Particles are Different particles moving all the have different sizes time. and masses. Fig. 6.3 The main points of the particle theory particle theory 粒子理論 148  6 Matter as Particles particle of the shot billiard ball shot enlarge If the shot was enlarged to the size of the Earth, the particles of the shot would be about the size shot of a billiard ball. Fig. 6.4 Comparing the sizes of the shot and its particles Classroom question Q: Is a sand grain a single Particles are far too small to be seen with the naked eye, or even particle? with a light microscope. In fact, they are far smaller than the cells A: No. A sand grain is a tiny solid made up of many we learned about in Unit 4. Study Fig. 6.5 below to have an idea sand particles. about how small particles are. We can see that a leaf is made up of cells. zoom in o cells n a leaf by around 40 0 times We can see that a cell is made up of ore sm tiny structures. ime in 10 t m zoo We can see that the water in the tiny structures are made up of far smaller particles. tiny structures zoom in fu rther by ar ound 100 time s particles Fig. 6.5 Seeing how small particles are by zooming in on a leaf Misconception Students may think that the spaces between shot 鉛球 the particles are occupied by air. Remind them that the spaces are empty spaces. 149 6 Matter as Particles All matter is made up of particles. The main points of the idea of particles are summarized in the particle theory. e-aristo.hk/r/ e-Checkpoint 6.1 iscpu6i01.e cp06s1 1. Write ‘T’ for a true statement and ‘F’ for a false statement. (a) All matter has mass and takes up space. T (b) All matter is made up of the same particles. F (c) The particles making up matter can be observed using a light microscope. F 2. Brownian motion can be observed in a smoke cell, which is filled with smoke and air. The photo on the right shows the path of the movement of a smoke particle seen under a path of movement microscope. smoke particle Explain the movement of the smoke particle. There are a lot of very tiny (a) air particles in the smoke cell and they are (b) smaller than the smoke particle. They are (c) moving in different directions. They (d) hit the smoke particle from different directions. This causes the smoke particle to move randomly. Section objectives Students should be able to C Evidence for the particle theory find evidence to support the claims of the particle Although particles are far too small to be seen, there are experiments theory. recognize that there are that can provide evidence to support the particle theory. Let us look empty spaces between at some of these experiments. particles. evidence 證據 150  SPS: OB, IF 6 Experiment 6.2 Matter as Particles Demonstration Experiment video e-aristo.hk/r/ isexptu6i02.e ev06s2 Can you smell the perfume contained in a balloon? Material and apparatus Caution Experiment preparation The balloon with perfume can Some students may be balloon (a few drops of perfume inside) 1 be prepared inside a fume allergic to perfume. cupboard. This helps students realize that the smell of the Procedure perfume is due to the perfume inside the balloon. balloon 1. Your teacher will show you a balloon with a few drops of perfume inside. perfume 2. Your teacher will pass the balloon around the class. Can you smell the perfume? Yes Discussion 1. What does the above result show us about the perfume particles? The perfume particles can pass through the balloon wall and go outside. 2. Explain your observation based on the particle theory. Also, complete the diagram below by drawing the particles of the balloon wall and those of the perfume. The wall of the balloon is made up of perfume particle balloon particle particles and there are spaces between these particles. The perfume particles are small enough to pass through these spaces and go outside. inside the balloon balloon outside the balloon wall 3. Which main points of the particle theory does the evidence from this experiment support? Put a ‘ ’ in the boxes for these main points below. All matter is made up of particles. Particles are very small. There are empty spaces between particles. Particles are moving all the time. Different matter is made up of different particles. Different particles have different sizes and masses. allergic 過敏的 151 6 Matter as Particles SPS: OB, PA, IF Experiment 6.3 e-aristo.hk/r/ Experiment video isexptu6i03.e ev06s3 Does the total volume change when water and alcohol are mixed? Material and apparatus 3 measuring cylinder (100 cm ) 3 ping-pong ball ~10 alcohol 3 beaker (1000 cm ) 1 marble ~10 Procedure Part A: Mixing the liquids 3 1. Fill two measuring cylinders, one with 50 cm of water and the other with 3 50 cm of alcohol. 2. If the water and alcohol are mixed, what do you think the total volume will be? 3 3 3 Less than 100 cm       100 cm       More than 100 cm (Answers may vary.) 3. Now, mix the water and the alcohol. Total volume = ? 3 3 50 cm of 50 cm of water alcohol 3 What is the total volume? (slightly less than 100 cm ) 3 4. Repeat Step 3 by using two cylinders of 50 cm water. Total volume = ? 3 3 50 cm of 50 cm of water water 3 What is the total volume? 100 cm Cont'd 152  6 Matter as Particles Part B: Mixing marbles and ping-pong balls 5. (a) Your teacher will show you a beaker containing some ping-pong balls. marble (b) Your teacher will add some marbles to the beaker and then mix the marbles and the ping-pong balls. What do you observe? beaker marbles ping-pong ball The get into the spaces between the ping-pong balls. Teaching notes Shaking the beaker gently can help Caution the marbles get into the spaces Add the marbles to the beaker gently. between the ping-pong balls. Otherwise, the beaker may break. Discussion 1. Based on the particle theory and the observation in Step 5 above, complete the diagram below and explain the result of mixing water and alcohol. alcohol water alcohol particle particle particle water particle water alcohol water + alcohol When the water and alcohol are mixed, the smaller water particles may get into the spaces between the larger alcohol particles. Therefore, the total volume is less than the sum of the volumes of the two liquids before they are mixed. 2. Which main points of the particle theory does the evidence from this experiment support? Put a ‘ ’ in the boxes for these main points below. All matter is made up of particles. Particles are very small. There are empty spaces between particles. Particles are moving all the time. Different matter is made up of different particles. Different particles have different sizes and masses. 153 6 Matter as Particles In Experiments 6.2 and 6.3, we have seen evidence to support the particle theory, as summarized in Table 6.1 below. Scientists have found evidence from many other experiments to support the particle theory. Today, the particle theory is widely accepted. It can be used to explain many properties of matter and phenomena in daily life, as we will see later in this Unit. Experiment Can you smell the perfume Does the total volume contained in a balloon? change when water and alcohol are mixed? (i) All matter is made up of particles. (ii) Particles are very small. (iii) There are empty spaces between particles. (iv) Particles are moving all the time. (v) Different matter is made up of different particles. (vi) Different particles have different sizes and masses. Table 6.1 The main points of the particle theory supported by the evidence from Experiments 6.2 and 6.3 Scientists have found evidence from experiments to support the particle theory. e-aristo.hk/r/ e-Checkpoint 6.2 iscpu6i02.e cp06s2 1. Peter has drawn the diagram on the right to show the particles in a mixture of water particle alcohol and water. air alcohol particle Cont'd phenomenon 現象 154  6 Matter as Particles Point out TWO mistakes in the diagram. (a) The water particles and alcohol particles should have different sizes. (b) The spaces between the particles are empty and should not be labelled as air. 2. Each of the following situations can be explained with some main points of the particle theory. Which are they? By referring to Table 6.1, write (i), (ii), (iii), etc. in the blanks below to represent these main points. (a) Spreading of smell (b) Leakage of air from the balloons Oh, grilled squid! Where We inflated the are you? I am coming… balloons a few days ago but they are much smaller now… (i), (iv) (i), (ii), (iii), (iv) 5-minute Quiz (Quiz 1: The particle theory) Section objectives D Different types of particles Students should be able to give examples of atoms and simple molecules. In the previous section, we learned that matter is made up of recognize that different particles. Let us look at Fig. 6.6 to study the particles of water more particles have different sizes and masses. closely. The particles of water consist of even smaller atoms: hydrogen atoms and oxygen atoms. Atoms are the basic types of particles making up matter. Teaching notes Students may feel hard to particle of water distinguish between atom, molecule and particle. The analogy below may help students distinguish: hydrogen atom Particle Food oxygen atom Atom Pork, shrimp Molecule Wonton (consists of pork and shrimps) Particle Food (includes pork and shrimps; also includes wontons) Fig. 6.6 The particles of water consist of atoms. atom 原子 hydrogen 氫 oxygen 氧 155 6 Matter as Particles There are more than 100 kinds of atoms and some substances are made up of only one kind of atom. For example, gold and iron are made up of gold atoms and iron atoms respectively. electric wire copper gold gold atom copper atom iron iron atom mercury mercury atom Fig. 6.7 Some examples of atoms Active learning Some substances are made up of small particles known as 3D model (Some common molecules) molecules. Molecules may consist of the same kind of atom, for Teaching notes example, oxygen molecules (Fig. 6.8a), or they may consist of Although there are only about 100 different kinds of atoms such as water molecules and carbon different kinds of atoms, there is a great variety of molecules. Different dioxide molecules (Fig. 6.8b and Fig. 6.8c). kinds of molecules consist of different numbers and different kinds of atoms. a oxygen atom b hydrogen atom c carbon atom oxygen atom oxygen atom an oxygen oxygen molecule a carbon dioxide (in the mask) consists of two a water molecule molecule consists of oxygen atoms consists of two two oxygen atoms hydrogen atoms and and one carbon atom one oxygen atom water carbon dioxide Fig. 6.8 Some examples of molecules (inside) molecule 分子 copper 銅 mercury 水銀/汞 156 carbon dioxide 二氧化碳  6 Matter as Particles Teaching notes Atoms and molecules are two different types of particles making up Besides atoms and molecules, ions are another substances. type of particle making up substances. For example, Particles of different substances have different sizes and masses. table salt is made up of sodium ions and chloride The table below shows the sizes and masses of some particles ions. compared to those of a hydrogen atom. Learn more Size* Mass* Atoms in our body The body of a 70 kg adult contains around 7 billion billion billion atoms, which is seven with 27 zeros after it! 1 In terms of numbers, the hydrogen atom percentages of the atoms are: 65% hydrogen 24% oxygen water molecule 2.6 10% carbon 1% others oxygen molecule 3.4 carbon dioxide 3.8 molecule Teaching notes Although a hydrogen atom is the lightest atom, it is not the smallest atom. A helium atom is the smallest atom. iron atom 2.9 2.7 copper atom Table 6.2 Sizes and masses of some particles (* The sizes and masses are relative to those of a hydrogen atom) 157 6 Matter as Particles Learn more Unit of measurement for Atoms are the basic types of particles the size of particles making up matter. The size of an atom or a molecule is usually measured A molecule consists of two or more atoms in nanometres (nm). It is a very joined together chemically. small unit of length: 1 nm = 1 millionth of mm Section objective Students should be aware E Chemical formula of a molecule that a simple molecule can be represented with a chemical Each molecule has its own chemical formula. The chemical formula formula (preparation for EXTENSION writing chemical equations in shows the types and the numbers of the atoms that the molecule Unit 7). [E] consists of. For example, an oxygen molecule consists of two oxygen atoms joined together. Its chemical formula is O 2. ‘O’ is the symbol for an oxygen atom, while the subscript ‘2’ means there are two oxygen atoms in one oxygen molecule. Similarly, the chemical formula of a water molecule is H 2O as it has two hydrogen atoms and one oxygen atom. oxygen atoms symbol of oxygen O2 represented by the chemical formula oxygen molecule O O the number of oxygen atoms in one molecule Teaching notes Remind students that the symbols in a chemical symbol of hydrogen formula are written in a oxygen atom H 2O represented by the symbol of oxygen definite order, e.g. for a water molecule: chemical formula water Correct: H2O molecule O Incorrect: OH2 H H omit ‘1’ here as there is only one oxygen hydrogen atoms atom in one molecule Fig. 6.9 Chemical formulae of an oxygen molecule and a water molecule A chemical formula shows the types and the numbers of the atoms that a molecule consists of. chemical formula 化學式 nanometre 納米 subscript 下標 158  6 Matter as Particles e-aristo.hk/r/ e-Checkpoint 6.3 iscpu6i03.e cp06s3 1. Write ‘T’ for a true statement and ‘F’ for a false statement. (a) A molecule consists of two or more atoms joined together chemically. T (b) There are more than 100 kinds of atoms. T (c) Molecules are usually smaller than atoms. F (d) All molecules consist of different kinds of atoms joined together. F E (e) A water molecule (chemical formula: H2O) consists of one hydrogen atom and two oxygen atoms. F 2. The diagrams below represent some particles. (i) (ii) (iii)            Which of the diagrams above best shows (a) an iron atom? (iii) (b) an oxygen molecule? (i) (c) a water molecule? (ii) E 3. Chemical formula NO H2 CO2 N2 Match each chemical formula given above with the molecule below by writing the chemical formula in the blanks provided. (a)   (b)   (c)   (d) HH N N N O O C O H2 N2 NO CO2 5-minute Quiz (Quiz 2: Different types of particles and chemical formulae) 159 6 Matter as Particles Prior knowledge In primary level, students Particle model for the three have learned that materials can be classified as solids, states of matter liquids or gases based on whether their shapes and volumes are fixed or not. The particle theory we learned in the previous section is useful as it can help explain different properties of matter. In this section, we will learn about the properties of matter in the three states and explain them by using the particle theory. Section objective Students should be able to A Properties of matter in the three states compare the properties of matter in different states. Matter can exist in three states: solid, liquid or gas. For example, water can exist as a solid (ice), a liquid (liquid water) or a gas (water Think about vapour). Can you name some examples of solids, liquids and gases around you? Matter in different states has different properties. Let us look at this Solids: pencil, ruler in the experiment below. Liquids: coke, juice Gases: air, oxygen SPS: OB, CS, PA Experiment 6.4 e-aristo.hk/r/ Experiment video isexptu6i04.e ev06s4 Comparing the properties of matter in different states Material and apparatus 3 wooden block 1 plastic syringe (20 cm , without needle) 1 3 beaker (250 cm ) 1 balloon 1 3 conical flask (250 cm ) 1 rubber band 1 Procedure 1. (a) Place a wooden block in a beaker. Does it take the shape of the beaker? beaker No (b) Take out the wooden block and place it on the wooden block bench. Then, press it with your finger. Can you compress it? No Cont'd solid 固體 compress 壓縮 liquid 液體 160 gas 氣體  6 Matter as Particles 2. (a) Half-fill a beaker with water. beaker (b) Pour the water into a conical flask. What happens to the shape of the water? water conical It takes up the shape of the conical flask. flask 3. (a) Half-fill a syringe with water. plunger push (b) Block the tip of the syringe with your finger and try to compress the water inside by pushing the plunger. water tip Can you compress the water? No 4. (a) Inflate a balloon with air until it is about the size of a fist. Then, tie its neck with a rubber band. (b) Try to squeeze the air inside the balloon. What happens to the shape of the air? squeeze The shape of the air changes. 5. (a) Half-fill a syringe with air. plunger push (b) Block the tip of the syringe with your finger and try to compress the air inside by pushing the plunger. air Can you compress the air? tip Yes Discussion From the results above, complete the following table to compare the properties of matter in different states. Does it have a fixed shape? Can it be compressed? Solid Yes No Liquid No No Gas No Yes inflate 充氣 squeeze 擠壓 161 6 Matter as Particles Teaching notes From Experiment 6.4, we found that solids have fixed volume and Solids and liquids can be compressed slightly under cannot be compressed. They also have fixed shape. very high pressure. Some solids (e.g. rubber) are more Liquids also have fixed volume and cannot be compressed. However, compressible than others. they have no fixed shape but take on the shapes of the containers But in general, solids and liquids cannot be easily holding them. compressed. Gases have no fixed volume and can be compressed. Like liquids, they have no fixed shape but take on the shapes of their containers. diving cylinder Fig. 6.10 Liquids have no fixed shape. Fig. 6.11 Air is compressed by about They take on the shapes of the containers 200 times (from 600 litres into 3 litres) holding them. when it is stored inside a diving cylinder. The properties of solids, liquids and gases: Have fixed shape? Have fixed volume? Solids Liquids Gases e-aristo.hk/r/ e-Checkpoint 6.4 iscpu6i04.e cp06s4 The key below can be used to classify matter into solids, liquids and gases. Fill in the blanks. Matter can be compressed cannot be compressed have fixed shape have no fixed shape (a) Gases (b) Solids (c) Liquids compress 壓縮 162  6 Matter as Particles Section objective Students should be able to B Particle model recognize the arrangement of particles in the three To explain the properties of matter in its three states, scientists have states of matter. proposed a particle model. Before we learn the particle model, let us first understand how models are used in science. 1. Models in science When scientists are designing an model aeroplane, they usually make a model of it and test the model in a wind tunnel. This helps the scientists study how the aeroplane will work. Teaching notes (Copyrighted Examples of models for photo by ONERA) illustrating structures or real systems: Fig. 6.12 The model of an aeroplane DNA model (Unit 4) in a wind tunnel the model of power generation using a steam engine (Experiment 5.2 in Unit 5) Examples of models for Scientists often use models to study and explain how things work. illustrating concepts: These models illustrate structures of objects, real systems as well as kinetic motion model explaining Brownian concepts. For example, we have used the kinetic motion model in motion (Fig. 6.13) Experiment 6.1 to explain Brownian motion of fat droplets in water. particle model i ea S n Differences between a model and a real system The model of a real system is not exactly the same as the real system. ball For example, in the DNA small model in Fig. 6.14, the beads shapes of the bases are not the same as those in real DNA. However, the bases model is still useful as it can show some important features of real DNA such as its double helix structure. Fig. 6.13 The kinetic motion model Fig. 6.14 A model showing the explaining Brownian motion structure of DNA model 模型 particle model 粒子模型 concept 概念 163 6 Matter as Particles Misconception 2. Arrangement and movement of particles Students may think that particles in solids stay still or in the three states of matter motionless. Remind them that the particles vibrate. Scientists have proposed a particle model based on the particle theory. The particle model helps describe the arrangements and movements of the particles in solids, liquids and gases. Solid Liquid Gas The particles The particles The particles are close together and are close together but are far apart. arranged regularly. arranged irregularly. can move freely in all cannot move from one can move around each directions. position to another, but other. can only vibrate about fixed positions. Particles in solids are like the Particles in liquids are like Particles in gases are like audience sitting in a cinema. the people in a crowd. The people running in all The audience are close and people are close, but can directions with a lot of space in a regular arrangement. move through the crowd. between them. Table 6.3 The particle model and its analogy particle model 粒子模型 analogy 比擬 164  6 SPS: OB Matter as Particles Activity 6.2 e-aristo.hk/r/ ac06s1 isactu6i01.e Studying the particle model Enter the code on our website to access a computer simulation of the particle model of a solid, a liquid and a gas. Watch the simulation closely and answer the questions below. 1. Similarities: The particles in both solid and liquid are close together. Differences: The particles in a solid are arranged regularly while the particles in a liquid are arranged irregularly. 1. Compare the arrangements of the particles in a solid and a liquid. What are the similarities and differences between the two arrangements? 2. Compare the arrangements of the particles in a liquid and a gas. What are the differences between the two arrangements? 2. The particles in a liquid are close together while the particles in a gas are far apart. 3. Compare the movement of the particles in a solid, a liquid and a gas. What are the differences you can observe? 3. The particles in a solid only vibrate about fixed positions. The particles in a liquid can move around each other. The particles in a gas can move freely. Scientists use the particle model to describe the arrangements and movements of particles in the three states of matter. 3. Explaining the properties of matter in the three states Let us use the particle model to explain the properties of solids, liquids and gases in the activity on the next page. 165 6 Matter as Particles Activity 6.3 Using the particle model to explain the properties of solids, liquids and gases The figures below show what happen to the shapes of a solid, a liquid and a gas when they are in different containers, and what happen to them when they are compressed. Complete the figures by drawing the particles in liquids and gases to show their arrangements. filling in the blanks to give explanations using the particle model. Solid A solid has a fixed shape because its particles cannot move from one Does it have a fixed shape? position to another. Yes push A solid cannot be compressed Can it be compressed? because its particles are close together. No Liquid A liquid does not have a fixed shape because its particles Does it have a fixed shape? can move around each other. No Can it be compressed? A liquid cannot be compressed because its particles No push are close together. Cont'd 166  6 Matter as Particles Gas A gas does not have a fixed Does it have a fixed shape? push push shape because its particles can move freely in all No directions. Can it be compressed? A gas can be compressed because its particles Yes push are far apart. e-aristo.hk/r/ e-Checkpoint 6.5 iscpu6i05.e cp06s5 1. Write ‘T’ for a true statement and ‘F’ for a false statement. (a) The particles in solids stay still. F (b) The particles in liquids can move freely in all directions. F (c) Liquid water and water vapour are made up of the same particles. T (d) Gases can be compressed because their particles are far apart. T 2. The figure on the left below shows the particles of a gas inside a container. Imagine the gas is transferred to a larger container. Draw the particles in the larger container below. transfer the gas to a larger container container larger container 5-minute Quiz Section Quiz 6.1–6.2 (Quiz 3: Particle model for the three states of matter) 167 6 Matter as Particles Classroom questions Q: Does the sugar still exist when it dissolves in Dissolving water? A: Yes, it still exists. Q: How do you know that the sugar still exists? A: The sugar solution tastes Mum, where does the sweet. sugar go when it dissolves in water? Misconception Some students may think that each grain of sugar is a sugar particle. Remind them that a sugar particle is much Fig. 6.15 Where does the sugar go when it dissolves in water? smaller and each grain of sugar consists of trillions of sugar particles. When sugar dissolves in water, the sugar seems to disappear. Can sugar you explain this using the particle theory? particle A Explaining dissolving by using the particle theory Section objective Students should be able to describe the process of dissolving using the particle theory. We can use the particle theory to explain what happens to sugar grain of sugar when it dissolves in water to form a sugar solution. From the particle theory, sugar is made up of sugar particles. Also, water is made up of water particles. When sugar dissolves in water, the sugar particles separate and mix with the water particles. The sugar particles are too small to be seen and therefore the sugar seems to disappear. However, the sugar is still there. This can be easily detected from the sweet taste of the solution formed. Fig. 6.16 Sugar is made up of sugar particles. dissolving dissolving sugar sugar particle water particle Sugar particles separate and Sugar particles and water particles mix with the water particles. are moving. They soon become evenly spread out. Fig. 6.17 When sugar dissolves in water, its particles separate and mix with the water particles. 168  6 SPS: OB, PA Matter as Particles Experiment 6.5 e-aristo.hk/r/ Experiment video isexptu6i05.e ev06s5 Observing the dissolving of potassium permanganate in water Material and apparatus 3 beaker (250 cm ) 1 glass rod 1 forceps 1 pair potassium permanganate crystal 1 Procedure Caution 3 1. Fill a beaker with 200 cm of water and put it on the bench. Do not touch potassium permanganate crystals. Wait until the water becomes still. They can cause irritation, and stain your skin and clothing brown. 2. (a) Use a pair of forceps to gently put a crystal of potassium permanganate into the water. (b) Wait for five minutes and then observe the contents of the beaker. Record your observation by completing the diagram below. water potassium permanganate crystal beginning after five minutes 3. Now use a glass rod to stir the solution gently until the crystal dissolves completely. Discussion Based on the particle model, complete the diagram below to show what happens to the potassium permanganate particles and water particles in the experiment. potassium permanganate crystal dissolves completely water particle potassium permanganate particle crystal 晶體 169 6 Matter as Particles Think about Melting (studied in Unit 2, Book 1A) and dissolving are When a solid dissolves in water, the particles of the solid different processes. Can separate and mix with the water you tell the differences using the particle theory? particles. Dissolving: The particles of the solute separate and mix with the particles of the solvent. The solution consists of two kinds B Do volume and mass change in of particles. dissolving? Melting: The particles become able to move around. The liquid When a solid dissolves in water, is the volume of the solution formed formed consists of only the equal to the sum of the volumes of the solid and water? How about original kinds of particles. the mass? We will find out in the following experiment. Section objectives Students should be able to SPS: OB, PA recognize that mass is conserved Experiment 6.6 when a solid is dissolved in water. Experiment video explain the change in volume when a ev06s6 solid is dissolved in water using the particle theory. Do volume and mass change when sugar dissolves in water? e-aristo.hk/r/ isexptu6i06.e Material and apparatus 3 measuring cylinder (100 cm ) 1 teaspoon 1 electronic balance 1 3 beaker (200 cm ) 1 plastic bottle (~500 mL, with a lid) 1 sugar long plastic rod 1 spatula 1 Experiment preparation Procedure 3 It takes about 5 minutes to dissolve 30 g of sugar in 100 cm of water. 3 3 Dissolving 30 g of sugar in 100 cm of water will result in about 2 cm decrease in volume. Part A: Observing any change of volume in dissolving 1. (a) Fill a beaker with water until it is about two-thirds full. (b) Add about six teaspoons of sugar ( ~ 30 g) to a measuring cylinder. beaker 2. Quickly add water from the beaker to the measuring cylinder, 3 until the water reaches the 100 cm mark. What is the total volume of the sugar and the water? 3 100 cm water 3. Use a plastic rod to stir the water in the measuring cylinder measuring cylinder gently until the sugar dissolves completely. What is the volume of the sugar solution formed? (Slightly less than 100 cm ) 3 sugar Caution Cont'd Do not stir the water vigorously. Otherwise, the measuring cylinder may break. 170  Teaching notes 3 3 (For Step 2) It is not easy to accurately measure out a volume, e.g. 30 cm of sugar as the 30 cm also includes 3 6 the volume of the space between sugar grains. Yet, what this experiment requires is a total volume of 100 cm before dissolving, and Step 2 ensures this as the water has filled the space between the sugar grains. Matter as Particles Part B: Observing any change of mass in dissolving 4. Remove the lid of a plastic bottle. Turn the lid upside-down and add sugar to it until it is full of sugar ( ~ 15 g). 5. Add water to the plastic bottle until it is about two-thirds full ( ~ 300 mL). 6. Measure the total mass of the lid with sugar and the bottle of water using an electronic balance. Record the plastic bottle total mass in the table in Step 8. water sugar lid electronic balance 7. (a) Remove the bottle and the lid from the electronic balance. Carefully transfer all the sugar into the bottle of water using a spatula. (b) Close the bottle tightly with the lid and shake it until all the sugar has dissolved. 8. Measure the total mass of the bottle of sugar solution (with the lid) using the electronic balance. Record the total mass in the table below. Before dissolving After dissolving Total mass (Answers may vary.) Is the mass of the sugar solution equal to the total mass of the sugar and the water before dissolving? Yes Discussion In dissolving, some variables have changed while some remain unchanged. State some of them below. (Examples of variables: mass, volume, etc.) Remain unchanged: mass Have changed: volume 171 6 Matter as Particles Based on the particle theory, there are spaces between particles. When sugar dissolves in water, the sugar particles separate. The smaller water particles fit into the spaces between the bigger sugar particles. Therefore, the volume of the solution is slightly less than the total volume of the sugar and water before dissolving. sugar particle water particle Fig. 6.18 Smaller water particles fit into the spaces between the bigger sugar particles. Unlike volume, mass remains unchanged in dissolving. Although the sugar particles separate, they are still in the water. The total number of the sugar particles and water particles remains the same. Therefore, the mass of the sugar solution is equal to the total mass of the sugar and the water before dissolving. In other words, mass is conserved in dissolving. water particle dissolving sugar particle Fig. 6.19 The total number of particles remains unchanged in dissolving so the mass is conserved. In dissolving, volume changes (changes / remains unchanged) while mass remains unchanged. 172  6 Matter as Particles e-aristo.hk/r/ e-Checkpoint 6.6 iscpu6i06.e cp06s6 1. Write ‘T’ for a true statement and ‘F’ for a false statement. (a) When a substance dissolves in water, the solution formed is made up of new particles different from the particles of the original substance. F (b) When sugar dissolves in water, the sugar particles do not take up any space in the solution. F (c) Mass is conserved in dissolving. T (d) A salt solution of 500 g is obtained when 100 g of salt is dissolved in 400 g of water. T 2. water particle sugar particle A sugar cube is added to a cup of water. The diagram above shows the particles in the cup before the sugar dissolves. Which of the following diagrams best shows the particles in the cup after the sugar has completely dissolved? A. B. C. D. D 5-minute Quiz (Quiz 4: Dissolving) 173 6 Matter as Particles Prior knowledge In primary level, students Thermal expansion and have learned that substances expand on contraction heating and contract on cooling. Have you ever seen the toy on the right? While you are holding the lower chamber upper chamber of the toy, the coloured liquid will rise and fill the upper chamber. Do you know how this works? You may understand more after this section. Teaching notes The gas in the lower chamber is heated by the hand. Thus, the gas expands and pushes the coloured liquid to rise along the glass tube at the centre of the chamber. Fig. 6.20 When you hold the lower lower chamber chamber of the toy, the coloured liquid will rise. Section objectives Students should be able to A Explaining thermal expansion and state the effect of contraction using the particle theory temperature change on the movement of particles. explain thermal expansion When a substance is heated, what will happen to its particles? How and contraction using the does this affect the properties of the substance? Let us study in the particle theory. activity below. SPS: OB Activity 6.4 e-aristo.hk/r/ ac06s2 isactu6i02.e Studying how temperature affects the movement of particles Enter the code on our website to access a computer simulation. The simulation shows the movement of particles in a solid, a liquid and a gas at different temperatures. Watch the simulation closely and answer the questions below. 1. Does the size of the particles change when the temperature increases? 1. No 2. How does the movement of the particles change when the temperature increases? 2. The particles move faster. 174 Misconception Students may think that particles stay at rest at 0 °C. Remind them that the particles still vibrate at 0 °C. In fact, 6 particles vibrate except that the temperature is at the absolute zero (–273.15 °C). Matter as Particles Learn more As seen from Activity 6.4, the movement of the particles of a substance is related to its temperature. When the temperature is The Eiffel Tower in different seasons higher, the particles move faster. When the temperature is lower, Due to thermal expansion they move slower. and contraction, the Eiffel Tower can be 15 cm taller in summer than in winter. From the movement of particles, we can understand the change in the size of a substance when it is heated or cooled. When a substance is heated, its particles move faster. Therefore, the particles are further apart and the substance as a whole increases in size. Similarly, when a substance is cooled, its particles move slower and become closer together, causing the substance as a whole to decrease in size. The above explains why most substances expand on he