MMMATTERATTERATTER INININ O O OURURUR S S

Chapter 1MATTERINOUR SURROUNDINGSAs we look at our surroundings, we see a largevariety of things with different shapes, sizesand textures. Everything in this universe ismade up of material which scientists havenamed “matter”. The air we breathe, the foodwe eat, stones, clouds, stars, plants andanimals, even a small drop of water or aparticle of sand – every thing is matter. Wecan also see as we look around that all thethings mentioned above occupy space andhave mass. In other words, they have bothmass* and volume**.Since early times, human beings havebeen trying to understand their surroundings.Early Indian philosophers classified matter inthe form of five basic elements – the“Panch Tatva”– air, earth, fire, sky and water.According to them everything, living or nonliving, was made up of these five basicelements. Ancient Greek philosophers hadarrived at a similar classification of matter.Modern day scientists have evolved twotypes of classification of matter based on theirphysical properties and chemical nature.In this chapter we shall learn aboutmatter based on its physical properties.Chemical aspects of matter will be taken upin subsequent chapters.1.1 Physical Nature of Matter1.1.1 MATTER IS MADE UP OF PARTICLESFor a long time, two schools of thought prevailedregarding the nature of matter. One schoolbelieved matter to be continuous like a blockof wood, whereas, the other thought that matterwas made up of particles like sand. Let usperform an activity to decide about the natureof matter – is it continuous or particulate?Activity 1.1 Take a 100 mL beaker.Fill half the beaker with water andmark the level of water.Dissolve some salt/ sugar with the helpof a glass rod.Observe any change in water level.What do you think has happened tothe salt?Where does it disappear?Does the level of water change?In order to answer these questions weneed to use the idea that matter is made upof particles. What was there in the spoon, saltor sugar, has now spread throughout water.This is illustrated in Fig. 1.1.Fig. 1.1: When we dissolve salt in water, the particlesof salt get into the spaces between particlesof water.1.1.2 HOWSMALL ARE THESE PARTICLESOF MATTER?Activity 1.2 T ake 2-3 crystals of potassiumpermanganate and dissolve them in100 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 islitre (L) such that 1L 1 dm3 , 1L 1000 mL, 1 mL 1 cm3.2021-22

Take out approximately 10 mL of thissolution and put it into 90 mL of clearwater.Take out 10 mL of this solution andput it into another 90 mL of clear water.Keep diluting the solution like this 5 to8 times.Is the water still coloured ? 1.2.2 P ARTICLESOFMATTERARECONTINUOUSLY MOVINGActivity 1.3 Put an unlit incense stick in a cornerof your class. How close do you have togo near it so as to get its smell?Now light the incense stick. Whathappens? Do you get the smell sittingat a distance?Record your observations.Activity 1.4 Fig. 1.2: Estimating how small are the particles ofmatter. With every dilution, though the colourbecomes light, it is still visible. This experiment shows that just a fewcrystals of potassium permanganate cancolour a large volume of water (about1000 L). So we conclude that there must bemillions of tiny particles in just one crystalof potassium permanganate, which keep ondividing themselves into smaller and smallerparticles.The same activity can be done using2 mL of Dettol instead of potassiumpermanganate. The smell can be detectedeven on repeated dilution.The particles of matter are very small –they are small beyond our imagination!!!! Activity 1.5 1.2 Characteristics of Particles ofMatter1.2.1 PARTICLES OF MATTER HAVE SPACE BETWEEN THEMIn activities 1.1 and 1.2 we saw that particlesof sugar, salt, Dettol, or potassiumpermanganate got evenly distributed in water.Similarly, when we make tea, coffee orlemonade (nimbu paani ), particles of one typeof matter get into the spaces between particlesof the other. This shows that there is enoughspace between particles of matter.Take two glasses/beakers filled withwater.Put a drop of blue or red ink slowlyand carefully along the sides of the firstbeaker and honey in the same way inthe second beaker.Leave them undisturbed in your houseor in a corner of the class.Record your observations.What do you observe immediately afteradding the ink drop?What do you observe immediately afteradding a drop of honey?How many hours or days does it takefor the colour of ink to spread evenlythroughout the water? Drop a crystal of copper sulphate orpotassium permanganate into a glassof hot water and another containingcold water. Do not stir the solution.Allow the crystals to settle at thebottom.What do you observe just above thesolid crystal in the glass?What happens as time passes?What does this suggest about theparticles of solid and liquid?Does the rate of mixing change withtemperature? Why and how?From the above three activities (1.3, 1.4 and1.5), we can conclude the following:2SCIENCE2021-22

Particles of matter are continuouslymoving, that is, they possess what we callthe kinetic energy. As the temperature rises,particles move faster. So, we can say that withincrease in temperature the kinetic energy ofthe particles also increases.In the above three activities we observethat particles of matter intermix on their ownwith each other. They do so by getting intothe spaces between the particles. Thisintermixing of particles of two different typesof matter on their own is called diffusion. Wealso observe that on heating, diffusionbecomes faster. Why does this happen?1.2.3 P ARTICLES Activity 1.7 Activity 1.8 Activity 1.6 Play this game in the field— make fourgroups and form human chains assuggested:The first group should hold eachother from the back and lock armslike Idu-Mishmi dancers (Fig. 1.3). MATTERQThe second group should hold handsto form a human chain.The third group should form a chainby touching each other with only theirfinger tips.Now, the fourth group of studentsshould run around and try to break thethree human chains one by one intoas many small groups as possible.Which group was the easiest to break?Why?INTake some water in a container, trycutting the surface of water with yourfingers.Were you able to cut the surface ofwater?What could be the reason behind thesurface of water remaining together?The above three activities (1.6, 1.7 and 1.8)suggest that particles of matter have forceacting between them. This force keeps theparticles together. The strength of this force ofattraction varies from one kind of matter toanother.Fig. 1.3 Take an iron nail, a piece of chalk anda rubber band.Try breaking them by hammering,cutting or stretching.In which of the above threesubstances do you think the particlesare held together with greater force?OF MATTER ATTRACTEACH OTHER If we consider each student as aparticle of matter, then in which groupthe particles held each other with themaximum force?uestions1.Which of the following arematter?Chair, air, love, smell, hate,almonds, thought, cold, lemonwater, smell of perfume.2. Give reasons for the followingobservation:The smell of hot sizzling foodreaches you several metresaway, but to get the smell fromcold food you have to go close.3. A diver is able to cut throughwater in a swimming pool. Whichproperty of matter does thisobservation show?4. What are the characteristics ofthe particles of matter?3OUR SURROUNDING S2021-22

1.3 States of Matterthe force is removed. If excessive force isapplied, it breaks.The shape of each individual sugar orsalt crystal remains fixed, whether wetake it in our hand, put it in a plate or ina jar.A sponge has minute holes, in whichair is trapped, when we press it, the airis expelled out and we are able tocompress it.Observe different types of matter around you.What are its different states? We can see thatmatter around us exists in three differentstates– solid, liquid and gas. These states ofmatter arise due to the variation in thecharacteristics of the particles of matter.Now, let us study about the properties ofthese three states of matter in detail. 1.3.1 THE SOLID STATE1.3.2 THE LIQUID STATE Activity 1.9Activity 1.10 Collect the following articles— a pen,a book, a needle and a piece of woodenstick.Sketch the shape of the above articlesin your notebook by moving a pencilaround them.Do all these have a definite shape,distinct boundaries and a fixed volume?What happens if they are hammered,pulled or dropped?Are these capable of diffusing into eachother?Try compressing them by applyingforce. Are you able to compress them? All the above are examples of solids. Wecan observe that all these have a definiteshape, distinct boundaries and fixed volumes,that is, have negligible compressibility. Solidshave a tendency to maintain their shape whensubjected to outside force. Solids may breakunder force but it is difficult to change theirshape, so they are rigid.Consider the following:(a) What about a rubber band, can itchange its shape on stretching? Is ita solid?(b) What about sugar and salt? Whenkept in different jars these take theshape of the jar. Are they solid?(c) What about a sponge? It is a solidyet we are able to compress it. Why?All the above are solids as: A rubber band changes shape underforce and regains the same shape when Collect the following:(a) water, cooking oil, milk, juice, acold drink.(b) containers of different shapes. Puta 50 mL mark on these containersusing a measuring cylinder fromthe laboratory.What will happen if these liquids arespilt on the floor?Measure 50 mL of any one liquid andtransfer it into different containers oneby one. Does the volume remain thesame?Does the shape of the liquid remain thesame ?When you pour the liquid from onecontainer into another, does it floweasily?We observe that liquids have no fixedshape but have a fixed volume. They take upthe shape of the container in which they arekept. Liquids flow and change shape, so theyare not rigid but can be called fluid.Refer to activities 1.4 and 1.5 where wesaw that solids and liquids can diffuse intoliquids. The gases from the atmospherediffuse and dissolve in water. These gases,especially oxygen and carbon dioxide, areessential for the survival of aquatic animalsand plants.All living creatures need to breathe forsurvival. The aquatic animals can breatheunder water due to the presence of dissolvedoxygen in water. Thus, we may conclude thatsolids, liquids and gases can diffuse intoliquids. The rate of diffusion of liquids is4SCIENCE2021-22