Most substances can be in three states: solid, liquid, and gas.

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1 States of Matter Most substances can be in three states: solid, liquid, and gas. Solid Particles Have Fixed Positions The particles in a solid are very close together and have an orderly, fixed arrangement. Solid particles can vibrate only in place and do not break away from their fixed positions. Solids have fixed volumes and shapes.

2 Three States of Matter

3 Mercury in Three States

4 States of Matter, continued Liquid Particles Can Move Easily Past One Another The particles in a liquid are very close together and have a random arrangement. Liquid particles have enough energy to be able to move past each other readily, which allows liquids to flow. Liquids have fixed volumes but can flow to take the shape of the lower part of a container.

5 States of Matter, continued Liquid Forces Lead to Surface Wetting and Capillary Action Liquid particles can have cohesion, attraction for each other. Liquid particles can also have adhesion, attraction for particles of solid surfaces. The balance of cohesion and adhesion determines whether a liquid will wet a solid surface. The forces of adhesion and cohesion will pull water up a narrow glass tube, called a capillary tube.

6 Comparing Cohesion and Adhesion

7 States of Matter, continued Liquids Have Surface Tension Below the surface of a liquid, the particles are pulled equally in all directions by cohesive forces. However, surface particles are pulled only sideways and downward, so they have a net downward force. It takes energy to oppose this net force and increase the surface area. The tendency of liquids to decrease surface area to the smallest size possible is surface tension.

8 Surface Tension

9 Surface Tension

10 Surface Tension Surface Tension Hydrogen bonds cause cohesion of H 2 O molecules. Surface tension is the name we give to the cohesion of water molecules at the surface of a body of water. Ready for a LAB activity????

11 Try this: Surface Tension Place a drop of water onto a piece of wax paper. Look closely at the drop. What shape is it? Why do you think it is this shape? What is happening?

12 Explanation: Surface Tension Water is not attracted to wax paper (there is no adhesion between the drop and the wax paper). Each molecule in the water drop is attracted to the other water molecules in the drop. This causes the water to pull itself into a shape with the smallest amount of surface area a bead (sphere). All the water molecules on the surface of the bead are holding each other together or creating surface tension.

13 Capillary Action Surface Tension Hydrogen bonds are also responsible for some the adhesive properties of water molecules. Capillary Action is a phenomenon where water will climb up a capillary tube due to the attraction between the H 2 O (polar) and the glass (or other polar material). The narrower the tube, the higher the water will climb. Capillary Tube

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15 Capillary Action Capillary Action Hydrogen bonds are also responsible for some the adhesive properties of water molecules. Capillary Action is a phenomenon where water will climb up a capillary tube due to the attraction between the H 2 O (polar) and the glass (or other polar material). The narrower the tube, the higher the water will climb. Capillary Tubes

16 Capillary Action Capillary Action Hydrogen bonds are also responsible for some the adhesive properties of water molecules. Capillary Action is a phenomenon caused by both cohesion and adhesion of water molecules. Ready for another LAB activity????

17 Capillary Action Try this: Place the edge of one end of a paper towel into a shallow container of water. What is happening? How can cohesion and adhesion of water explain this? What effect do you think temperature might have? How could you test this?

18 Explanation: Capillary Action The pores in the paper towel act like capillary tubes. The water molecules (polar) are attracted to the molecules in the paper towel (also polar). When a water molecule is attracted to the paper towel molecules (adhesion), the nearby water molecules are pulled along with it (cohesion). Ex: plants use capillary action to move water up from the ground.

19 Capillary Action

20 States of Matter, continued Gas Particles Are Essentially Independent The particles in a gas are very far apart and have a random arrangement. The attractive forces between particles in a gas do not have a great effect, so the particles move almost independently of one another. The shape, volume, and density of an amount of gas change depending on the size and shape of the container.

21 Comparison of Solid, Liquid, and Gas State Shape and Volume Compressibility Ability to Flow Gas Conforms to shape and volume of container Particles can move past one another High Lots of free space between particles Flows easily Particles can move past one another Liquid Conforms to shape of container Volume limited by surface Particles can move/slide around each other Not easily compressible Little free space between particles Flows easily Particles can move around each other Solid Maintains a fixed volume and shape Rigid particles are locked in place Not easily compressible Little free space between particles Does not flow easily Particles cannot move around

22 Changes of State

23 Changing States, continued Liquid Evaporates to Gas Energy is required to separate liquid particles. They gain energy when they collide with each other. If a particle gains a large amount of energy, it can leave the liquid s surface and join gas particles. Evaporation is the change of state from liquid to gas. Evaporation is an endothermic process. Boiling point is the temperature and pressure at which a liquid and a gas are in equilibrium.

24 Changing States, continued Evaporation is the change of state from liquid to gas. It is an endothermic process. Boiling point is the temperature and pressure at which a liquid and a gas are in equilibrium.

25 Changing States, continued Gas Condenses to Liquid When gas particles no longer have enough energy to overcome the attractive forces between them, they go into the liquid state. Condensation is the change of state from a gas to a liquid. Condensation is an exothermic process. Condensation can take place on a cool night, causing water vapor in the air to form dew on plants.

26 Visual Concepts Vaporization and Condensation

27 Changing States, continued Solid Melts to Liquid As a solid is heated, the particles vibrate faster and faster in their fixed positions. At a certain temperature, some of the molecules have enough energy to break out of their fixed positions. Melting is the change of state from solid to liquid. Melting is an endothermic process. Melting point is the temperature and pressure at which a solid becomes a liquid.

28 Changing States, continued Liquid Freezes to Solid As a liquid is cooled, the movement of particles becomes slower and slower. At a certain temperature, the particles are pulled together into the fixed positions of the solid state. Freezing is the change of state from a liquid to a solid. Freezing is an exothermic process. Freezing point is the temperature at which a substance freezes.

29 Visual Concepts Freezing

30 Changing States, continued Solid Sublimes to Gas The particles in a solid are constantly vibrating. Some particles have higher energy than others. Particles with high enough energy can escape from the solid. Sublimation is the change of state from solid to gas. Sublimation is an endothermic process.

31 Changing States, continued Gas Deposits to Solid Molecules in the gaseous state become part of the surface of a crystal. When a substance changes state from a gas to a solid, the change is often called deposition. Deposition is an exothermic process.

32 Visual Concepts Comparing Sublimation and Deposition

33 Visual Concepts Comparing Melting and Sublimation Carbon Dioxide Water Room temperature and normal atmospheric pressure

34 Phase change summary

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