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IGCSE CHEMISTRY CHAPTER 1: PARTICULATE NATURE OF MATTER Walter Aaron Wong BSc, MSc, MRSB CHAPTER 1 The Particulate Nature of Matter States of Matter Kinetic Theory of Matter Changes in the States of Matter Diffusion What matters? 1. Chemistry is about...

IGCSE CHEMISTRY CHAPTER 1: PARTICULATE NATURE OF MATTER Walter Aaron Wong BSc, MSc, MRSB CHAPTER 1 The Particulate Nature of Matter States of Matter Kinetic Theory of Matter Changes in the States of Matter Diffusion What matters? 1. Chemistry is about what matter is like and how it behaves. 2. The word matter is used to cover all the substances and materials from which the physical universe is composed. 3. Matter is anything that occupies space and has mass. 4. There are millions of substances known known, and all of them can be catagorised as either solids, liquids or gases. 5. These 3 states of substances are known as the states of matter. Solids, Liquids and Gases 1. Solid, at a given temperature has the following properties: Has a fixed volume and shape Slightly affected by temperature change Usually increase slightly in size when it is heated (expansion) Usually decrease in size when cooled (contraction) 2. Liquid, at a given temperature has the following properties: Has a fixed volume but follows the shape of its container Slightly affected by temperature change Usually increase slightly in size when it is heated (expansion) Usually decrease in size when cooled (contraction) 3. Gas, at a given temperature has the following properties: Has no fixed volume Follows the shape of the container Volume is greatly affected by changes in temperature Increase in size when it is heated Decrease in size when it is cooled 4. Liquid and gases are relatively compressible. 5. Their volume can be reduced by the application of pressure. 6. Gases are more compressible than liquids. The Kinetic Theory of Matter 1. The kinetic theory of matter helps to explain the way in which matter behaves. 2. According to this theory, all matter is made up of tiny particles. 3. This theory explains the physical properties of matter in terms of the movement of particles. 4. The main points of the theory are: All matter is made up of tiny particles. Different substances have different types of particles (atoms, ions, molecules) which have different sizes. The particles are in constant motion. Heavier particles move slower compared to lighter particles (at a constant temperature). The movement of particles are affected by temperature (the higher the temperature, the faster the movement of particles). 5. In a solid, the particles: Attract one another by strong forces of attraction Are held very close to one another. Have very little freedom to move and can only vibrate in a fixed position. Are arranged in a regular manner 6. The arrangement and properties if the particles in a solid explain why many solids form crystals. Sodium chloride model and crystals 7. In liquid, the particles: Are close together but not as close as solid particles. Move around in random directions and often collide with one another. Have forces of attraction which are weaker than solid particles. Have more energy than particles in a solid. Are not arranged in a regular manner. 8. In gases, the particles: Are relatively far apart. Are free to move anywhere within the container. Move randomly at very high velocities and much more rapidly compared to liquid particles. Collide with one another but less often compared liquid particles. They collide often with the walls of the container. Have very weak or almost negligible forces of attraction among one another but they do exist. Changes of the States of Matter SOLID to LIQUID 1. The kinetic theory of matter can be used to explain how substances change from one state of matter to another. 2. When a solid is heated, the particles gain kinetic energy and vibrate faster. 3. This makes the particles “push” their neighbouring particles further away from themselves. 4. This causes an increase in the volume of the solid and the solid expands. 5. Eventually, the heat energy causes the forces of attraction between the particles to weaken. 6. The regular pattern of particle arrangement will break down and the particles will break free from one another. 7. The particles will now be able to move around each other. 8. The solid is said to be melted and has turned into the liquid state. 9. The temperature in which solid melts is called the melting point of a substance. 10. Solids have high melting points because the particles have strong forces of attraction. 11. A lot of heat energy is required to melt a solid. LIQUID to GAS 1. When liquid is heated, the particles will gain more kinetic energy move around even faster. 2. Some particles at the surface of the liquid have enough energy to overcome the forces of attraction between themselves and they escape to form a gas. 3. The liquid begins to evaporate from the surface. 4. This process is known as evaporation. 5. Eventually, a temperature is reached at which the particles are trying to escape from the liquid so quickly that bubbles of gas start to form inside the bulk of the liquid. 6. The liquid then boils to form gas. 7. This temperature is called the boiling point of a substance. 8. Liquids with high boiling points have stronger forces between their particles. GAS to LIQUID to SOLID 1. Kinetic energy decreases as temperature decreases. 2. When gas is cooled, the kinetic energy of the particles decreases. 3. When this happens, the particles move slower and closer to one another. 4. The forces of attraction between the particles now become significant and causes the gas to condense into liquid. 5. This process is known as condensation. 6. As the temperature continues to drop, the liquid will eventually freeze to form a solid. 7. This process is known as freezing. 8. During each of the event of cooling and changes of state of matter, energy is given out. *Changes of state are examples of physical changes. Whenever a physical change of state occurs, the temperature remains constant during the change. Also, during a physical change, no new substance is formed. An Unusual Change of State 1. There are a few substances that change directly from solid to gas when they are heated without going through the liquid state. 2. This process is known as sublimation. 3. The cooling of these kind of substances changes their state from gas directly back to solid as well. 4. Examples of substances which can undergo sublimation are carbon dioxide and iodine. 5. Carbon dioxide is a white solid called dry ice at temperature below -78°C. 6. When it is heated to just above -78°C, it changes to carbon dioxide gas. Sublimation of dry ice (solid carbon dioxide). Sublimation of iodine crystals Heating and Cooling Curves 1. A heating or cooling curve can tell us what is going on during the change of the states of matter. 2. The graph below shows the heating curve of water when it is heated steadily from -15°C to 110°C. 3. When the temperature was first measured, only ice was present. 4. After a short period of time, the curve flattens, showing that even though heat energy is being put in, the temperature remains constant. 5. There’s no change of temperature at this phase because the heat energy supplied is absorbed by the water particles in a solid form. 6. The particles of water are very close together and the forces of attraction between the particles are strong. 7. For ice to melt, the particles must obtain enough energy to overcome the forces of attraction between the water particles. 8. Once enough energy is absorbed, the forces of attraction between the water particles will weaken and the particles will be able to break free from the solid arrangement. 9. The water particles will then be able to move around one another. 10. When this happens, solid water (ice) melts to become liquid water. 11. The melting point of water is at 0°C. 12. The temperature will begin to rise again only after all the ice has melted. 13. After the ice has melted, there is a sharp increase of temperature from 0° to 100°C. 14. At 100°C, the curve flattens again. 15. At this point, there is no change of temperature because the energy supplied is absorbed by the water particles in the liquid form to overcome the forces of attraction among one another. 16. Once enough energy is absorbed, the water particles will be able to break free from the liquid liquid state and move further apart from one another. 17. At this stage, liquid water will turn into gaseous water (water vapour) and boiling has occurred. 18. The boiling point of water is 100°C. 19. If the melting point or boiling point of a particular substance is higher or lower than usual, that indicates a presence of impurities. 20. Melting point of a particular substance can be determined by an experiment as shown below: Diffusion – Evidence for Moving Particles 1. Have you ever wondered how you get to smell the perfumes when you walk past a cosmetics store? 2. For this to happen, gas particles from the perfume bottles must fill the air around the store’s area. 3. The spreading of gas in the surrounding air is called diffusion. 4. Diffusion can be defined as the movement of substances from a region of higher concentration to a region of lower concentration. 5. All gases diffuse to fill the space available randomly and evenly. 6. Brown-red bromine gas spreads evenly throughout both gas jars after 24 hours as shown below:  7. Gases diffuse at different rates. 8. Some gases will travel in higher velocities while some will be slower. 9. Below shows an experimental set up to investigate the reaction between concentrated ammonia solution and hydrochloric acid: White fume of ammonium chloride Hydrochloric Ammonia acid 10. In the glass tube, a cotton ball soaked with concentrated hydrochloric acid is placed at the edge of the tube on the left while a cotton ball soaked with concentrated ammonia is placed at the edge of the tube on the right. 11. The white fumes produced as shown in the picture is ammonia chloride, which is a product of the reaction between the fumes of ammonia and hydrochloric acid. 12. The white fume is produced nearer to the left cotton ball because ammonia particles are lighter, and they have a smaller relative molecular mass than the hydrogen chloride particles. 13. Diffusion also takes place in liquids, but it is a much slower process than in gases. 14. This is because the particles of a liquid move much more slowly. 15. Diffusion can also take place between a liquid and a gas. This is known as intimate mixing. 16. In this process, the gaseous particles and the liquid particles collide among one another randomly. 17. There is enough space between the particles for this to happen. CHAPTER REVIEW EXERCISE 1. Define matter. (1 mark) 2. Give 3 examples of matter. (3 marks) 3. Give 3 examples of non-matter. (3 marks) 4. State 3 states of matter. (3 marks) 5. When a state of matter changes, does it involve energy? (1 mark) 6. When a state of matter changes, is it a physical change or a chemical change? Explain why. (2 marks) 7. State the name of an unusual change in state of matter. Also, give two examples. (3 marks) 8. What is Brownian Movement? (1 mark) 9. State the definition of diffusion. (1 mark) 10. Using labelled diagrams, explain how diffusion works. (5 marks) Answers: IGCSE FOCUS QUESTIONS 1. Compare the arrangement and movement of molecules in solid oxygen and gaseous oxygen. (3 marks) 2. In balloon filled with helium gas, the atoms of helium collide with the walls of the balloon to create gas pressure. The gas pressure can be felt when we try push the walls of the balloon inwards. When temperature increases, the wall of the balloon feels a little more firm and harder. Explain this phenomenon according to the Kinetic Theory. (3 marks) 3. Concentrated ammonia gives off ammonia gas and concentrated hydrochloric acid gives off hydrogen chloride gas. Both gases are colourless. Ammonia reacts with hydrogen chloride to produce ammonium chloride, which is a white solid. Apparatus is set up as shown below: After 10 minutes, a white solid form in the tube where the gases of ammonia and hydrogen chloride meet. a) Write the word equation for the reaction above. (1 mark) b) Name the process by which ammonia gas and hydrogen chloride gas moves in the tube. (1 mark) c) At which point (A, B, C or D) will the gases meet? (1 mark) d) Explain why based on your answer in (c). (2 marks) e) If the experiment is repeated at a higher temperature, what will you observe? Explain why. (2 marks)