As we look at our surroundings, we see a large variety of things with different shapes, sizes and textures. Everything in this universe is made up of material which scientists have named “matter”. The air we breathe, the food we eat, stones, clouds, stars, plants and animals, even a small drop of water or a particle of sand — every thing is matter. We can also see as we look around that all the things mentioned above occupy space and have mass. In other words, they have both mass* and volume**. Since early times, human beings have been trying to understand their surroundings. Early Indian philosophers classified matter in the 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 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.
1.1.1 MATTER IS MADE UP OF PARTICLES.
For a long time, two schools of thought prevailed regarding the nature of matter. One school believed matter to be continuous like a block of wood, whereas, the other thought that matter was made up of particles like sand. Let us perform an activity to decide about the nature of matter — is it continuous or particulate
This experiment shows that just a few crystals of potassium permanganate can colour a large volume of water (about 1000 L). So we conclude that there must be millions of tiny particles in just one crystal of potassium permanganate, which keep on dividing themselves into smaller and smaller particles. The same activity can be done using 2 ml of Dettol instead of potassium permanganate. The smell can be detected even on repeated dilution. The particles of matter are very small – they are small beyond our imagination!!!!
Matter.
BETWEEN THEM
In activities 1.1 and 1.2 we saw that particles of sugar, salt, Dettol, or potassium permanganate got evenly distributed in water. Similarly, when we make tea, coffee or lemonade (nimbu paani ), particles of one type of matter get into the spaces between particles of the other. This shows that there is enough space between particles of matter.
Particles of matter are continuously moving, that is, they possess what we call the kinetic energy. As the temperature rises, particles move faster. So, we can say that with increase in temperature the kinetic energy of the particles also increases. In the above three activities we observe that particles of matter intermix on their own with each other. They do so by getting into the spaces between the particles. This intermixing of particles of two different types of matter on their own is called diffusion. We also observe that on heating, diffusion becomes faster. Why does this happen?
EACH OTHER.
Play this game in the field— make four groups and form human chains as suggested: • The first group should hold each other from the back and lock arms like Idu-Mishmi dancers (Fig. 1.3). Fig. 1.3 • The second group should hold hands to form a human chain. • The third group should form a chain by touching each other with only their finger tips. • Now, the fourth group of students should run around and try to break the three human chains one by one into as many small groups as possible. • Which group was the easiest to break? Why?
If we consider each student as a particle of matter, then in which group the particles held each other with the maximum force? Activity ______________ 1.7 • Take an iron nail, a piece of chalk and a rubber band. • Try breaking them by hammering, cutting or stretching. • In which of the above three substances do you think the particles are held together with greater force? Activity ______________ 1.8 • Take some water in a container, try cutting the surface of water with your fingers. • Were you able to cut the surface of water? • What could be the reason behind the surface of water remaining together? The above three activities (1.6, 1.7 and 1.8) suggest that particles of matter have force acting between them. This force keeps the particles together. The strength of this force of attraction varies from one kind of matter to another.
CIENCE1.3 States of Matter Observe different types of matter around you.What are its different states? We can see that matter around us exists in three different states– solid, liquid and gas. These states of matter arise due to the variation in the characteristics of the particles of matter.Now, let us study about the properties of these three states of matter in detail.1.3.1 THE SOLID State Activity _____________ 1.9• Collect the following articles — a pen,a book, a needle and a piece of wooden stick.• Sketch the shape of the above articles in your notebook by moving a pencil around 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 applying force. Are you able to compress them?All the above are examples of solids. We Can observe that all these have a definite shape, distinct boundaries and fixed volumes,that is, have negligible compressibility. Solids Have a tendency to maintain their shape when subjected to outside force. Solids may break under force but it is difficult to change the shape, so they are rigid.Consider the following:(a) What about a rubber band, can change its shape on stretching? Is ita solid?(b) What about sugar and salt? When Kept in different jars these take the shape of the jar. Are they solid?(c) What about a sponge? It is a solid yet 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 the force is removed. If excessive force is applied, it breaks.• The shape of each individual sugar or salt crystal remains fixed, whether we take it in our hand, put it in a plate or ina jar.• A sponge has minute holes, in which air is trapped, when we press it, the airis expelled out and we are able to compress it.1.3.2 THE LIQUID State Activity _____________1.10• Collect the following:(a) water, cooking oil, milk, juice, cold drink.(b) containers of different shapes. Puta 50 mL mark on these containers using a measuring cylinder from the laboratory.• What will happen if these liquids poured on the floor?• Measure 50 mL of any one liquid and transfer it into different containers one by one. Does the volume remain the same?• Does the shape of the liquid remain the same ?• When you pour the liquid from one container into another, does it flow easily?We observe that liquids have no friendship but have a fixed volume. They take up the shape of the container in which they are kept. Liquids flow and change shape, so they are not rigid but can be called fluid.Refer to activities 1.4 and 1.5 where we saw that solids and liquids can diffuse into liquid. The gases from the atmosphere diffuse and dissolve in water. These gases,especially oxygen and carbon dioxide, are essential for the survival of aquatic animals and plants.All living creatures need to breathe for survival. The aquatic animals can breathe under water due to the presence of dissolved oxygen in water. Thus, we may conclude that solid, liquids and gases can diffuse into liquid. The rate of diffusion of liquids is higher than that of solids. This is due to the fact that in the liquid state, particles move freely and have greater space between each other as compared to particles in the solid state. 1.3.3 THE GASEOUS STATE Have you ever observed a balloon seller filling a large number of balloons from a single cylinder of gas? Enquire from him how many balloons is he able to fill from one cylinder. Ask him which gas does he have in the cylinder. Activity _____________1.11 • Take three 100 mL syringes and close their nozzles by rubber corks, as shown in Fig.1.4. • Remove the pistons from all the syringes. • Leaving one syringe untouched, fill water in the second and pieces of chalk in the third. • Insert the pistons back into the syringes. You may apply some vaseline on the pistons before inserting them into the syringes for their smooth movement. • Now, try to compress the content by pushing the piston in each syringe. We have observed that gases are highly compressible as compared to solids and liquids. The liquefied petroleum gas (LPG) cylinder that we get in our home for cooking or the oxygen supplied to hospitals in cylinders is compressed gas. Compressed natural gas (CNG) is used as fuel these days in vehicles. Due to its high compressibility, large volumes of a gas can be compressed into a small cylinder and transported easily. We come to know of what is being cooked in the kitchen without even entering there, by the smell that reaches our nostrils. How does this smell reach us? The particles of the aroma of food mix with the particles of air spread from the kitchen, reach us and even farther away. The smell of hot cooked food reaches us in seconds; compare this with the rate of diffusion of solids and liquids. Due to high speed of particles and large space between them, gases show the property of diffusing very fast into other gases. In the gaseous state, the particles move about randomly at high speed. Due to this random movement, the particles hit each other and also the walls of the container. The pressure exerted by the gas is because of this force exerted by gas particles per unit area on the wall of the container.
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 particles of matter during the change of state? How does this change of state take place?
On increasing the temperature of solids,the kinetic energy of the particles increases.Due to the increase in kinetic energy, the particles start vibrating with greater speed.The energy supplied by heat overcomes the force of attraction between the particles. The Particles leave their fixed positions and start moving more freely. A stage is reached when the solid melts and is converted to a liquid.The minimum temperature at which a solid melts to become a liquid at the atmospheric pressure is called its melting point.The melting point of a solid is an indication of the strength of the force of attraction between its particles.The melting point of ice is 273.15 K*. The Process of melting, that is, change of solid state into liquid state is also known as fusion.When a solid melts, its temperature remains the same, so where does the heart energy go?You must have observed, during the experiment of melting, that the temperature of the system does not change after the melting point is reached, till all the ice melts.This happens even though we continue to heat the beaker, that is, we continue to supply heat. This heat gets used up in changing thestate by overcoming the forces of attraction between the particles. As this heat energy is absorbed by ice without showing any rise temperature, it is considered that it gets hidden into the contents of the beaker and is known as the latent heat. The word latent means hidden. The amount of heat energy that is required to change 1 kg of a solid into liquid at atmospheric pressure at its melting point is known as the latent heat of fusion.So, particles in water at 0°C (273 K) have more energy as compared to particles in ice at the same temperature.When we supply heat energy to water,particles start moving even faster. At a certain temperature, a point is reached when the particles have enough energy to break free from the forces of attraction of each other. Atthis temperature the liquid starts changing into gas. The temperature at which a liquid starts boiling at the atmospheric pressure is known as its boiling point. Boiling is a bulk phenomenon. Particles from the bulk of the liquid gain enough energy to change into the vapour state.For water this temperature is 373 K(100oC = 273 + 100 = 373 K).Can you define the latent heat evaporation? So, we infer that the state of matter can be changed into another state by changing the temperature.We have learnt that substances around us change state from solid to liquid and from liquid to gas on application of heat. But there Do it in the same way as we have defined the latent heat of fusion.Particles in steam, that is, water vapour at373 K (1000 C) have more energy than water at the same temperature. This is because particles in steam have absorbed extra energy in the form of latent heat of vaporisation are some that change directly from solid state to gaseous state and vice versa without changing into the liquid state.