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C hapter 1 MATTER IN OUR SURROUNDINGS As we look at our surroundings, we see a large Activity ______________ 1.1 variety of things with different shapes, sizes and textures. Everything in this universe is Take a 100 mL beaker....

C hapter 1 MATTER IN OUR SURROUNDINGS As we look at our surroundings, we see a large Activity ______________ 1.1 variety of things with different shapes, sizes and textures. Everything in this universe is Take a 100 mL beaker. Fill half the beaker with water and made up of material which scientists have mark the level of water. named “matter”. The air we breathe, the food Dissolve some salt/ sugar with the help we eat, stones, clouds, stars, plants and of a glass rod. animals, even a small drop of water or a Observe any change in water level. particle of sand — every thing is matter. We What do you think has happened to can also see as we look around that all the the salt? things mentioned above occupy space and Where does it disappear? have mass. In other words, they have both Does the level of water change? mass* and volume**. In order to answer these questions we Since early times, human beings have need to use the idea that matter is made up been trying to understand their surroundings. of particles. What was there in the spoon, salt Early Indian philosophers classified matter in or sugar, has now spread throughout water. the form of five basic elements — the “Panch This is illustrated in Fig. 1.1. Tatva” — air, earth, fire, sky and water. According to them everything, living or non- living, was made up of these five basic elements. Ancient Greek philosophers had arrived at a similar classification of matter. Modern day scientists have evolved two types of classification of matter based on their physical properties and chemical nature. In this chapter we shall learn about matter based on its physical properties. Chemical aspects of matter will be taken up in subsequent chapters. Fig. 1.1: When we dissolve salt in water, the particles of salt get into the spaces between particles 1.1 Physical Nature of Matter of water. 1.1.1 MATTER IS MADE UP OF PARTICLES 1.1.2 HOW SMALL ARE THESE PARTICLES For a long time, two schools of thought prevailed regarding the nature of matter. One school OF MATTER? believed matter to be continuous like a block of wood, whereas, the other thought that matter Activity ______________ 1.2 was made up of particles like sand. Let us Take 2–3 crystals of potassium perform an activity to decide about the nature permanganate and dissolve them in of matter — is it continuous or particulate? 100 mL of water. * The SI unit of mass is kilogram (kg). ** The SI unit of volume is cubic metre (m3). The common unit of measuring volume is litre (L) such that 1L = 1 dm3, 1L = 1000 mL, 1 mL = 1 cm3. 2024-25  Take out approximately 10 mL of this 1.2.2 P ARTICLES OF MATTER ARE solution and put it into 90 mL of clear water. CONTINUOUSLY MOVING Take out 10 mL of this solution and put it into another 90 mL of clear water. Keep diluting the solution like this 5 to Activity 1.3 8 times. Is the water still coloured ? Put an unlit incense stick in a corner of your class. How close do you have to go near it so as to get its smell? Now light the incense stick. What happens? Do you get the smell sitting at a distance? Record your observations. Activity 1.4 Take two glasses/beakers filled with Fig. 1.2: Estimating how small are the particles of water. matter. With every dilution, though the colour Put a drop of blue or red ink slowly becomes light, it is still visible. and carefully along the sides of the first beaker and honey in the same way in This experiment shows that just a few the second beaker. crystals of potassium permanganate can Leave them undisturbed in your house colour a large volume of water (about or in a corner of the class. 1000 L). So we conclude that there must be Record your observations. millions of tiny particles in just one crystal What do you observe immediately after of potassium permanganate, which keep adding the ink drop? on dividing themselves into smaller and What do you observe immediately after smaller particles. adding a drop of honey? The same activity can be done using 2 mL How many hours or days does it take of Dettol instead of potassium permanganate. for the colour of ink to spread evenly The smell can be detected even on throughout the water? repeated dilution. The particles of matter are very small – Activity 1.5 they are small beyond our imagination!!!! Drop a crystal of copper sulphate or 1.2 Characteristics of Particles of potassium permanganate into a glass of hot water and another containing Matter cold water. Do not stir the solution. Allow the crystals to settle at the 1.2.1 PARTICLES OF MATTER HAVE SPACE bottom. BETWEEN THEM What do you observe just above the solid crystal in the glass? In activities 1.1 and 1.2 we saw that particles What happens as time passes? of sugar, salt, Dettol, or potassium What does this suggest about the permanganate got evenly distributed in water. particles of solid and liquid? Similarly, when we make tea, coffee or Does the rate of mixing change with lemonade (nimbu paani ), particles of one type temperature? Why and how? of matter get into the spaces between particles From the above three activities (1.3, 1.4 and of the other. This shows that there is enough 1.5), we can conclude the following: space between particles of matter. 2 SCIENCE 2024-25  Particles of matter are continuously If we consider each student as a moving, that is, they possess what we call particle of matter, then in which group the kinetic energy. As the temperature rises, the particles held each other with the maximum force? particles move faster. So, we can say that with increase in temperature the kinetic energy of the particles also increases. Activity ______________ 1.7 In the above three activities we observe Take an iron nail, a piece of chalk and that particles of matter intermix on their own a rubber band. with each other. They do so by getting into Try breaking them by hammering, the spaces between the particles. This cutting or stretching. intermixing of particles of two different types In which of the above three of matter on their own is called diffusion. We substances do you think the particles also observe that on heating, diffusion are held together with greater force? becomes faster. Why does this happen? Activity ______________ 1.8 1.2.3 PARTICLES OF MATTER ATTRACT Take some water in a container, try EACH OTHER cutting the surface of water with your fingers. Activity ______________ 1.6 Were you able to cut the surface of water? Play this game in the field— make four What could be the reason behind the groups and form human chains as surface of water remaining together? suggested: The first group should hold each The above three activities (1.6, 1.7 and 1.8) other from the back and lock arms suggest that particles of matter have force like Idu-Mishmi dancers (Fig. 1.3). acting between them. This force keeps the particles together. The strength of this force of attraction varies from one kind of matter to another. Q uestions 1. Which of the following are matter? Chair, air, love, smell, hate, almonds, thought, cold, lemon water, smell of perfume. 2. Give reasons for the following Fig. 1.3 observation: The second group should hold hands The smell of hot sizzling food to form a human chain. reaches you several metres The third group should form a chain away, but to get the smell from by touching each other with only their cold food you have to go close. finger tips. 3. A diver is able to cut through Now, the fourth group of students water in a swimming pool. Which should run around and try to break the property of matter does this three human chains one by one into observation show? as many small groups as possible. Which group was the easiest to break? 4. What are the characteristics of Why? the particles of matter? M AT T E R IN O U R S U R R O U N D I N GS 3 2024-25 1.3 States of Matter the force is removed. If excessive force is applied, it breaks. Observe different types of matter around you. The shape of each individual sugar or What are its different states? We can see that salt crystal remains fixed, whether we matter around us exists in three different take it in our hand, put it in a plate or in states– solid, liquid and gas. These states of a jar. matter arise due to the variation in the A sponge has minute holes, in which characteristics of the particles of matter. air is trapped, when we press it, the air Now, let us study about the properties of is expelled out and we are able to these three states of matter in detail. compress it. 1.3.1 THE SOLID STATE 1.3.2 THE LIQUID STATE Activity _____________ 1.9 Activity _____________ 1.10 Collect the following articles — a pen, Collect the following: a book, a needle and a piece of wooden (a) water, cooking oil, milk, juice, a stick. cold drink. Sketch the shape of the above articles (b) containers of different shapes. Put in your notebook by moving a pencil a 50 mL mark on these containers around them. using a measuring cylinder from Do all these have a definite shape, the laboratory. distinct boundaries and a fixed volume? What will happen if these liquids are What happens if they are hammered, spilt on the floor? pulled or dropped? Measure 50 mL of any one liquid and Are these capable of diffusing into each transfer it into different containers one other? by one. Does the volume remain the same? Try compressing them by applying Does the shape of the liquid remain the force. Are you able to compress them? same ? All the above are examples of solids. We When you pour the liquid from one can observe that all these have a definite container into another, does it flow shape, distinct boundaries and fixed volumes, easily? that is, have negligible compressibility. Solids We observe that liquids have no fixed have a tendency to maintain their shape when shape but have a fixed volume. They take up subjected to outside force. Solids may break the shape of the container in which they are under force but it is difficult to change their kept. Liquids flow and change shape, so they shape, so they are rigid. are not rigid but can be called fluid. Refer to activities 1.4 and 1.5 where we Consider the following: saw that solids and liquids can diffuse into (a) What about a rubber band, can it liquids. The gases from the atmosphere change its shape on stretching? Is it diffuse and dissolve in water. These gases, a solid? especially oxygen and carbon dioxide, are (b) What about sugar and salt? When essential for the survival of aquatic animals kept in different jars these take the and plants. shape of the jar. Are they solid? All living creatures need to breathe for (c) What about a sponge? It is a solid survival. The aquatic animals can breathe yet we are able to compress it. Why? under water due to the presence of dissolved All the above are solids as: oxygen in water. Thus, we may conclude that A rubber band changes shape under solids, liquids and gases can diffuse into force and regains the same shape when liquids. The rate of diffusion of liquids is 4 SCIENCE 2024-25 higher than that of solids. This is due to the We have observed that gases are highly fact that in the liquid state, particles move compressible as compared to solids and freely and have greater space between each liquids. The liquefied petroleum gas (LPG) other as compared to particles in the solid cylinder that we get in our home for cooking state. or the oxygen supplied to hospitals in cylinders is compressed gas. Compressed 1.3.3 THE GASEOUS STATE natural gas (CNG) is used as fuel these days in vehicles. Due to its high compressibility, Have you ever observed a balloon seller filling large volumes of a gas can be compressed a large number of balloons from a single into a small cylinder and transported easily. cylinder of gas? Enquire from him how many We come to know of what is being cooked balloons is he able to fill from one cylinder. in the kitchen without even entering there, Ask him which gas does he have in the cylinder. by the smell that reaches our nostrils. How does this smell reach us? The particles of the Activity _____________ 1.11 aroma of food mix with the particles of air spread from the kitchen, reach us and even Take three 100 mL syringes and close farther away. The smell of hot cooked food their nozzles by rubber corks, as shown in Fig.1.4. reaches us in seconds; compare this with the Remove the pistons from all the rate of diffusion of solids and liquids. Due to syringes. high speed of particles and large space Leaving one syringe untouched, fill between them, gases show the property of water in the second and pieces of chalk diffusing very fast into other gases. in the third. In the gaseous state, the particles move Insert the pistons back into the about randomly at high speed. Due to this syringes. You may apply some vaseline random movement, the particles hit each on the pistons before inserting them other and also the walls of the container. The into the syringes for their smooth pressure exerted by the gas is because of this movement. force exerted by gas particles per unit area Now, try to compress the content by pushing the piston in each syringe. on the walls of the container. Fig. 1.4 What do you observe? In which case Fig.1.5: a, b and c show the magnified schematic was the piston easily pushed in? pictures of the three states of matter. The What do you infer from your motion of the particles can be seen and observations? compared in the three states of matter. M AT T E R IN O U R S U R R O U N D I N GS 5 2024-25  uestions 1.4.1 EFFECT OF CHANGE OF TEMPERATURE Q 1. The mass per unit volume of a substance is called density. (density = mass/volume). Arrange the following in order of increasing density – air, exhaust from chimneys, honey, water, chalk, cotton and iron. 2. (a) Tabulate the differences in the characterisitcs of states Activity _____________ 1.12 Take about 150 g of ice in a beaker and suspend a laboratory thermometer so that its bulb is in contact with the ice, as in Fig. 1.6. of matter. (b) Comment upon the following: rigidity, compressibility, fluidity, filling a gas container, shape, kinetic energy and density. 3. Give reasons (a) A gas fills completely the vessel in which it is kept. (b) A gas exerts pressure on the walls of the container. (c) A wooden table should be called a solid. (d) We can easily move our hand (a) in air but to do the same through a solid block of wood we need a karate expert. 4. Liquids generally have lower density as compared to solids. But you must have observed that ice floats on water. Find out why. 1.4 Can Matter Change its State? We all know from our observation that water can exist in three states of matter– solid, as ice, liquid, as the familiar water, and gas, as water vapour. What happens inside the matter during this change of state? What happens to the (b) particles of matter during the change of states? How does this change of state take place? We need answers to these questions, Fig. 1.6: (a) Conversion of ice to water, (b) conversion isn’t it? of water to water vapour 6 SCIENCE 2024-25  Start heating the beaker on a low flame. state by overcoming the forces of attraction Note the temperature when the ice between the particles. As this heat energy is starts melting. absorbed by ice without showing any rise in Note the temperature when all the ice temperature, it is considered that it gets has converted into water. hidden into the contents of the beaker and is Record your observations for this known as the latent heat. The word latent conversion of solid to liquid state. means hidden. The amount of heat energy Now, put a glass rod in the beaker and that is required to change 1 kg of a solid into heat while stirring till the water starts liquid at atmospheric pressure at its melting boiling. point is known as the latent heat of fusion. Keep a careful eye on the thermometer So, particles in water at 0oC (273 K) have more reading till most of the water has vaporised. energy as compared to particles in ice at the Record your observations for the same temperature. conversion of water in the liquid state When we supply heat energy to water, to the gaseous state. particles start moving even faster. At a certain temperature, a point is reached when the On increasing the temperature of solids, particles have enough energy to break free the kinetic energy of the particles increases. from the forces of attraction of each other. At Due to the increase in kinetic energy, the this temperature the liquid starts changing particles start vibrating with greater speed. into gas. The temperature at which a liquid The energy supplied by heat overcomes the starts boiling at the atmospheric pressure is forces of attraction between the particles. The known as its boiling point. Boiling is a bulk particles leave their fixed positions and start phenomenon. Particles from the bulk of the moving more freely. A stage is reached when liquid gain enough energy to change into the the solid melts and is converted to a liquid. vapour state. The minimum temperature at which a solid For water this temperature is 373 K melts to become a liquid at the atmospheric (100oC = 273 + 100 = 373 K). pressure is called its melting point. Can you define the latent heat of vaporisation? Do it in the same way as we The melting point of a solid is an indication have defined the latent heat of fusion. of the strength of the force of attraction Particles in steam, that is, water vapour at between its particles. 373 K (1000 C) have more energy than water at the same temperature. This is because The melting point of ice is 273.15 K*. The particles in steam have absorbed extra energy process of melting, that is, change of solid in the form of latent heat of vaporisation. state into liquid state is also known as fusion. When a solid melts, its temperature remains the same, so where does the heat energy go? You must have observed, during the experiment of melting, that the temperature So, we infer that the state of matter can of the system does not change after the be changed into another state by changing melting point is reached, till all the ice melts. the temperature. This happens even though we continue to We have learnt that substances around heat the beaker, that is, we continue to supply us change state from solid to liquid and from heat. This heat gets used up in changing the liquid to gas on application of heat. But there *Note: Kelvin is the SI unit of temperature, 0o C =273.15 K. For convenience, we take 0o C = 273 K after rounding off the decimal. To change a temperature on the Kelvin scale to the Celsius scale you have to subtract 273 from the given temperature, and to convert a temperature on the Celsius scale to the Kelvin scale you have to add 273 to the given temperature. M AT T E R IN O U R S U R R O U N D I N GS 7 2024-25 are some that change directly from solid state enclosed in a cylinder? Will the particles come to gaseous state and vice versa without closer? Do you think that increasing or changing into the liquid state. decreasing the pressure can change the state of matter? Activity _____________ 1.13 Take some camphor. Crush it and put it in a china dish. Put an inverted funnel over the china dish. Put a cotton plug on the stem of the funnel, as shown in Fig. 1.7. Fig. 1.8: By applying pressure, particles of matter can be brought close together Applying pressure and reducing temperature can liquefy gases. Have you heard of solid carbon dioxide (CO2)? It is stored under high pressure. Solid CO2 gets converted directly into gaseous state on decrease of pressure to 1 atmosphere* without coming into liquid state. This is the Fig. 1.7: Sublimation of camphor reason that solid carbon dioxide is also known as dry ice. Now, heat slowly and observe. Thus, we can say that pressure and What do you infer from the above temperature deter mine the state of a activity? substance, whether it will be solid, liquid A change of state directly from solid to gas or gas. without changing into liquid state is called sublimation and the direct change of gas to solid without changing into liquid is called deposition. 1.4.2 EFFECT OF CHANGE OF PRESSURE We have already learnt that the difference in various states of matter is due to the Deposition difference in the distances between the constituent particles. What will happen when we start putting pressure and compress a gas Fig. 1.9: Interconversion of the three states of matter * atmosphere (atm) is a unit of measuring pressure exerted by a gas. The unit of pressure is Pascal (Pa): 1 atmosphere = 1.01 × 105 Pa. The pressure of air in atmosphere is called atmospheric pressure. The atmospheric pressure at sea level is 1 atmosphere, and is taken as the normal atmospheric pressure. 8 SCIENCE 2024-25 Q dish and keep it inside a cupboard or uestions on a shelf in your class. 1. Convert the following temperature Record the room temperature. to celsius scale: Record the time or days taken for the a. 300 K b. 573 K evaporation process in the above cases. 2. What is the physical state of Repeat the above three steps of activity water at: on a rainy day and record your a. 250oC b. 100oC ? observations. 3. For any substance, why does the What do you infer about the effect of temperature remain constant temperature, surface area and wind during the change of state? velocity (speed) on evaporation? 4. Suggest a method to liquefy You must have observed that the rate of atmospheric gases. evaporation increases with– an increase of surface area: 1.5 Evaporation We know that evaporation is a surface Do we always need to heat or change pressure phenomenon. If the surface area is for changing the state of matter? Can you increased, the rate of evaporation quote some examples from everyday life where increases. For example, while putting change of state from liquid to vapour takes clothes for drying up we spread them out. place without the liquid reaching the boiling an increase of temperature: point? Water, when left uncovered, slowly With the increase of temperature, more changes into vapour. Wet clothes dry up. What number of particles get enough kinetic happens to water in the above two examples? energy to go into the vapour state. We know that particles of matter are a decrease in humidity: always moving and are never at rest. At a given Humidity is the amount of water vapour temperature in any gas, liquid or solid, there present in air. The air around us cannot are particles with different amounts of kinetic hold more than a definite amount of energy. In the case of liquids, a small fraction of particles at the surface, having higher water vapour at a given temperature. If kinetic energy, is able to break away from the the amount of water in air is already high, forces of attraction of other particles and gets the rate of evaporation decreases. converted into vapour. This phenomenon of an increase in wind speed: change of liquid into vapours at any It is a common observation that clothes temperature below its boiling point is called dry faster on a windy day. With the evaporation. increase in wind speed, the particles of water vapour move away with the wind, 1.5.1 FACTORS AFFECTING decreasing the amount of water vapour EVAPORATION in the surrounding. Let us understand this with an activity. 1.5.2 HOW DOES EVAPORATION CAUSE COOLING? Activity _____________ 1.14 In an open vessel, the liquid keeps on Take 5 mL of water in a test tube and evaporating. The particles of liquid absorb keep it near a window or under a fan. energy from the surrounding to regain the Take 5 mL of water in an open china energy lost during evaporation. This dish and keep it near a window or absorption of energy from the surroundings under a fan. make the surroundings cold. Take 5 mL of water in an open china M AT T E R IN O U R S U R R O U N D I N GS 9 2024-25  What happens when you pour some Why do we see water droplets on the outer acetone (nail polish remover) on your palm? surface of a glass containing ice-cold The particles gain energy from your palm or water? surroundings and evaporate causing the palm Let us take some ice-cold water in a to feel cool. tumbler. Soon we will see water droplets on After a hot sunny day, people sprinkle the outer surface of the tumbler. The water water on the roof or open ground because vapour present in air, on coming in contact the large latent heat of vaporisation of water with the cold glass of water, loses energy and helps to cool the hot surface. gets converted to liquid state, which we see Can you cite some more examples from as water droplets. daily life where we can feel the effect of cooling due to evaporation? uestions Q Why should we wear cotton clothes in summer? 1. Why does a desert cooler cool During summer, we perspire more better on a hot dry day? because of the mechanism of our body which 2. How does the water kept in an keeps us cool. We know that during earthen pot (matka) become cool evaporation, the particles at the surface of during summer? the liquid gain energy from the surroundings 3. Why does our palm feel cold or body surface and change into vapour. The when we put some acetone or heat energy equal to the latent heat of petrol or perfume on it? vaporisation is absorbed from the body 4. Why are we able to sip hot tea or leaving the body cool. Cotton, being a good milk faster from a saucer rather absorber of water helps in absorbing the than a cup? sweat and exposing it to the atmosphere for 5. What type of clothes should we easy evaporation. wear in summer? What you have learnt Matter is made up of small particles. The matter around us exists in three states—solid, liquid and gas. The forces of attraction between the particles are maximum in solids, intermediate in liquids and minimum in gases. The spaces in between the constituent particles and kinetic energy of the particles are minimum in the case of solids, intermediate in liquids and maximum in gases. 10 SCIENCE 2024-25  The arrangement of particles is most ordered in the case of solids, in the case of liquids layers of particles can slip and slide over each other while for gases, there is no order, particles just move about randomly. The states of matter are inter-convertible. The state of matter can be changed by changing temperature or pressure. Sublimation is the change of solid state directly to gaseous state without going through liquid state. Deposition is the change of gaseous state directly to solid state without going through liquid state. Boiling is a bulk phenomenon. Particles from the bulk (whole) of the liquid change into vapour state. Evaporation is a surface phenomenon. Particles from the surface gain enough energy to overcome the forces of attraction present in the liquid and change into the vapour state. The rate of evaporation depends upon the surface area exposed to the atmosphere, the temperature, the humidity and the wind speed. Evaporation causes cooling. Latent heat of vaporisation is the heat energy required to change 1 kg of a liquid to gas at atmospheric pressure at its boiling point. Latent heat of fusion is the amount of heat energy required to change 1 kg of solid into liquid at its melting point. Some measurable quantities and their units to remember: Quantity Unit Symbol Temperature kelvin K Length metre m Mass kilogram kg Weight newton N Volume cubic metre m3 Density kilogram per cubic metre kg m–3 Pressure pascal Pa M AT T E R IN O U R S U R R O U N D I N GS 11 2024-25  Exercises 1. Convert the following temperatures to the celsius scale. (a) 293 K (b) 470 K 2. Convert the following temperatures to the kelvin scale. (a) 25o°C (b) 373o°C 3. Give reason for the following observations. (a) Naphthalene balls disappear with time without leaving any solid. (b) We can get the smell of perfume sitting several metres away. 4. Arrange the following substances in increasing order of forces of attraction between the particles— water, sugar, oxygen. 5. What is the physical state of water at— (a) 25o°C (b) 0o°C (c) 100o°C ? 6. Give two reasons to justify— (a) water at room temperature is a liquid. (b) an iron almirah is a solid at room temperature. 7. Why is ice at 273 K more effective in cooling than water at the same temperature? 8. What produces more severe burns, boiling water or steam? 9. Name A,B,C,D,E and F in the following diagram showing change in its state 12 SCIENCE 2024-25  Group Activity Prepare a model to demonstrate movement of particles in solids, liquids and gases. For making this model you will need A transparent jar A big rubber balloon or piece of stretchable rubber sheet A string Few chickpeas or black gram or dry green peas. How to make? Put the seeds in the jar. Sew the string to the centre of the rubber sheet and put some tape to keep it tied securely. Stretch and tie the rubber sheet on the mouth of the jar. Your model is ready. Now run your fingers up and down the string by first tugging at it slowly and then rapidly. Fig. 1.10: A model for converting of solid to liquid and liquid to gas. M AT T E R IN O U R S U R R O U N D I N GS 13 2024-25