Particulate Model of Matter

22.1 What Matter is Made Up of What is matter made up of? Ancient Greek philosophers thought that matter was made up of fire, air, earth and water. However, scientists today have deduced from experiments that matter is made up of tiny particles that are in constant and random motion.

22.2 Evidence for Moving Particles The spreading of smells, such as from cooking or perfumes, is because of the movement of tiny particles in air. These particles move about randomly in all directions, and hence the smells spread. We say that diffusion has taken place. Diffusion is a process by which particles of matter move from a region of higher concentration to a region of lower concentration.

Experiment 1: Diffusion in Gases Prepare a gas jar of bromine vapour by placing a few drops of liquid bromine in the gas jar. Then invert a gas jar containing air over it. Observe what happens. After some time, both gas jars become filled uniformly with a reddish-brown colouration Evidence for Moving Particles

Diffusion also occurs in liquids. However, it takes place more slowly than in gases. This shows that particles in a liquid move around more slowly than in gases.

Experiment 2: Diffusion in Liquids Place a few crystals of potassium permanganate at the bottom of a beaker of water. Leave the set-up to stand and observe it from time to time. After a few days, the purple colouration of potassium permanganate will spread throughout the mixture Evidence for Moving Particles water potassium permanganate crystals At the beginning After a few days

22.3 Particulate Model of Matter PropertySolidsLiquidsGases ShapeHave fixed shapes Have no fixed shapes Take the shape of their containers Have no fixed shape Take the shape of their containers VolumeHave fixed volumes Have no fixed volume Fill up the space of their containers CompressibilityCannot be compressed Can be compressed

22.3 Particulate Model of Matter Scientists use the particulate model of matter to explain that the three states of matter are different because of the differences in the movement (motion) and arrangement of the particles. We can use the particulate model to explain why the behaviour of solids, liquids and gases differs form one another.

Particulate model of solids The particles in the solid state: oare strongly attracted to each other oare packed very closely together oare arranged in a fixed, regular pattern; and ocan only vibrate about their fixed positions.

Particulate model of solids The particles in a solid are unable to move freely. Thus, a solid has a definite shape and volume. There is no space between the particles to enable them to get any closer to one another. This is why solids cannot be compressed.

Particulate model of liquids The particles in the liquid state: oare attracted to one another; oare packed closely together; oare not arranged in a fixed, regular pattern; and ocan move over short distances.

Particulate model of liquids The particles in the liquid state are farther away from one another than the particles in a solid. However, the particles in a liquid are still held closely together. Thus, like solids, liquids have a fixed volume and cannot be compressed. Unlike solids, the particles in a liquid are not fixed in regular positions and are able to slide past one another. This is why a liquid has no definite shape.

Particulate model of gases The particles in the gaseous state: oare weakly attracted to one another oare far apart from one another; and ocan move freely in any direction.

Particulate model of gases The particles in a gas are spaced far apart from one another and so a gas can be compressed easily. The particles are also able to move freely to occupy any available space. This explains why a gas has no definite shape or volume.

22.4 Changes of States of Matter Matter can exist in the solid, liquid or gaseous state, depending on its temperature and atmospheric pressure. At a fixed pressure, the temperature of an object will determine its state. Boiling occurs when ice is heated to a temperature of 0 0 C and above. Boiling occurs when liquid water is heated to a temperature of C. Freezing occurs when water is cooled to 0 0 C and below. Condensation occurs when water vapour is cooled to a temperature of C and below.

Melting When a solid is strongly heated, the particles gain energy and vibrate more vigorously in their fixed positions. When the particles have enough energy (i.e. reach the melting point), they break free from one another and move about randomly. The particles are no longer held in fixed positions, but they are still close to one another. This change in arrangement and motion of particles is known as melting. Solid Liquid Gain in energy

Freezing When a liquid is cooled, the particles lose energy and they move about more slowly. As the temperature falls, the particles lose more and more energy until they are close enough to allow the forces of attraction to make them return to their fixed positions. The substance has changed from a liquid to a solid. This change in arrangement and motion of particles is called freezing. LiquidSolid Loss in energy

Boiling When a liquid is heated, the particles gain energy and vibrate and move about more vigorously. When the particles have enough energy (i.e reach the boiling point), they break free from one another. The particles become randomly arranged, very far apart and moving about at great speeds. This change in arrangement and motion of the particles is known as boiling. Liquid Gas Gain in energy

Condensation When a gas is cooled, the particles lose energy and they move about less vigorously and at lower speeds. As the temperature falls, the particles lose more and more energy until they are close enough to be attracted to one another. The substance has turned from a gas to a liquid. This change in arrangement and motion of particles is known as condensation. GasLiquid Loss in energy

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