Ch.8.particle theory

The particle theory, states of matter properties, changes in state of matter, gas pressure, diffusion and atmospheric pressure

1. The particle theory Chapter 8 (Chemistry)

2. The particle theory of matter The particle theory states that matter is made from particles . The particles are s tiny that they cannot be seen with the naked eye. Different substances are made from different particles and the particles have different sizes. The particles are made from atoms and molecules .

3. The properties of matter and the particle theory There are 3 states of matter and each one has its own special properties

4. Strong attraction forces hold the particles together in a 3 dimensional structure . The orderly arrangement is called lattice. Particles can move a little (do not change position), they vibrate. Solids Particles in a solid Properties of solids Solids have a definite mass. They have a definite volume. They are hard to compress. They do not flow.

5. Forces that hold the particles together are weaker than solids. Particles in a liquid can change position by moving around each other. Liquids Particles in a liquid Properties of liquids Liquids have a definite mass. They have a definite volume. They are hard to compress. They flow. They take the shape of the container.

6. Forces that hold the particles together are very small. Particles can move away from each other and travel in all directions. When they hit each other or the walls of the container they bounce and change direction Gases Particles in a gas Properties of gases Gases have indefinite mass. They have indefinite volume. They are easy to compress. They flow and spread. They take the shape of the container.

7. When states of matter change. This type of change is a physical change and is reversible. Melting, freezing, evaporating, boiling, condensing and sublimation are all examples.

8. Melting (solid changing into a liquid) When solid is heated to its melting point it loses shape and starts to flow . The heat energy supplied makes the particles vibrate more strongly so they push each other away. This weakens the forces of attraction between the particles and allows them to move around each other.

9. Freezing (Liquid changing into a solid) When liquid is cooled to its freezing point the particles lose energy and can no longer move around each other. The particles vibrate in one position in a lattice.

10. Evaporation (liquid changing into a gas) A liquid can change into gas over a range of temperatures without boiling . Some of the liquid at the surface changes into gas and mixes with the air as it has more energy than the rest of the particles in the liquid.

11. Boiling When the liquid reaches its boiling point bubbles of gas form in it which rise to the surface and burst into the air . If the boiling liquid is heated strongly, its temperature does not rise, it just boils quickly.

12. Condensing (gas changes into liquid) When a gas is cooled it condenses to form a liquid . The particles in the gas lose some of the energy which allows them to move so quickly and they slow down so much that they cannot bounce off each other. They stay close to each other and form a liquid.

13. Sublimation (solid changes into gas or gas into solid) Few substances can change from solid to gas or from gas to solid without forming a liquid. The forces are quickly lost or formed when the particles quickly gain or lose energy.

14. Dissolving (solid dissolves in a liquid) When a solid dissolves in a liquid it seems to disappear into it. If it is a coloured substance it may colour the liquid. It does not disappear, the particles separate and spread through the liquid. This is possible because the liquid has gaps between its particles, so the particles of the dissolving substances pass into them.

15. Gas pressure Solids can generate pressure , example : a brick on your toes. Liquids and gases can generate pressure too. Example: The dam You can see from the diagram that the dam is much thicker at the bottom than it is at the top. This is because the pressure of the water is much greater deeper down and the dam needs to be thick at the bottom so that it is strong enough to withstand this larger pressure

16. If there is a hole in the container’s surface then liquid will flow out, at greater depths .... force & pressure are greater .... escaping liquid is greater

17. Atmospheric pressure The atmosphere is a mixture of gases that covers the surface of the earth (1000 km thick). It pushes on every cm² of earth’s surface. The unit of atmospheric pressure is N/cm² Atmospheric pressure at sea level is called the standard pressure (1o N/cm²) This is the pressure at which the boiling point of any substance is measured

18. Boiling and low pressure If a flask containing a liquid is connected to a vacuum pump and some of the air above the liquid is sucked out, there is less air inside the flask to push on the surface of the liquid ( smaller air pressure ). The reduced air pressure allows evaporation to take place more quickly (less heat needed), so the boiling point is lowered .

19. Boiling and high pressure When a gas gets hot it expands and increases its pressure on the surfaces around it. If water is boiled in a pan with a lid, the steam escaping from the water pushes on the lid and makes it rise (allowing the gas to escape).

20. Diffusion (Process in which one substance spreads out through another)