Chapter 7 Introduction to Matter

1. Chapter 7Introduction to Matter Pearson Grade 8

2. Lesson 1: Describing Matter

3. Matter: anything that has mass and takes up space. • Chemistry: the study of matter and how matter changes. • Complete the Figure 1 exercise “Properties of Matter” on page 259. • Substances: a single kind of matter that has a specific makeup or composition. It is always the same.

4. Elements • All matter in the universe is made up of more than 100 different substances called elements. • An element is a substance that cannot be broken down into any other substances by physical or chemical means. • Elements are the simplest substances. • Each element can be identified by its specific physical and chemical properties. • Elements are represented by one- or two-letter symbols. • C for carbon, • O for oxygen, and • Ca for calcium. • Complete the “apply it!” exercise on page 260.

5. Atoms • Atoms: The particle theory of matter says that all matter is made of atoms. • An atom is the basic particle from which all elements are made. • An atom has a positively charged center, or nucleus, containing protons and neutrons. • The nucleus is surrounded by a “cloud” of negatively charged electrons. • Different elements have different properties because their atoms are different.

6. Molecules • Molecules: Atoms of most elements are able to combine with other atoms. • A chemical bond is the force of attraction between two atoms. • A molecule is a group of two or more atoms held together by chemical bonds. • Complete the “Compare and Contrast” exercise on page 261.

7. Complete the Fig 2 exercise “Atoms and Molecules” on pg 261.

8. Compounds • A compound is a substance made of two or more elements that are chemically combined in a set ratio. • A compound is represented by a chemical formula which shows the elements in the compound and the ratio of atoms. • In one molecule of CO2 there is one atom of carbon and two atoms of oxygen. • When elements chemically combine, they form compounds with properties different from those of the elements. • Complete the Figure 3 exercise “Compounds from Elements” on page 262.

9. Mixtures • A mixture is made of two or more substances that are together in the same place but their atoms are not chemically bonded. Each substance in a mixture keeps its own properties. Parts of a mixture are not combined in a set ratio. • Heterogeneous Mixtures: the parts of a heterogeneous mixture can be separated. • Homogenous Mixtures: the parts of a homogeneous mixture are evenly mixed and difficult to separate. A solution is an example of a homogeneous mixture. • Complete the Figure 4 exercise “Fruit Mixtures” exercise on pages 262-263. • Complete the “Assess Your Understanding” including the “got it?” on page 263. • Complete the “Review and Assessment” Questions #1-4 on page 283.

10. Lesson 2: States of Matter

11. How do you describe a solid? • A solid has a definite shape and a definite volume. It keeps the shape and volume in any container. • Particles in a solid: the particles that make up a solid are packed very closely together in a fixed position. This closely packed arrangement of particles causes the solid to have a definite shape and volume. The particles move slightly by vibrating in place.

12. Complete the Figure 1 Exercise “Solid” including the blue table on page 265.

13. Types of Solids • Crystalline solids are made of crystals. • A crystal is a solid with particles in a regular, repeating pattern. • Examples include salt, sugar, and snow. • Crystalline solids melt at a distinct temperature. • Amorphous solids have particles that are not arranged in a regular repeating pattern. • Instead of melting at a distinct temperature, an amorphous solid may become softeror change into another substance when heated. • Examples include glass, plastics, and rubber. • Complete the Figure 2 “Types of Solids” exercise on page 266. • Complete the “Assess Your Understanding” including the “got it?” on page 266.

14. How do you Describe a Liquid? • A liquid has a definite volume but no shape of its own. The shape of a liquid may change with its container, but its volume remains the same. • Particles of a liquid: The particles of a liquid are packed together less closely than those in a solid. The particles in a liquid can slide around each other but still touch. A liquid is sometimes called a fluid.

15. Complete the Figure 3 “Liquid” exercise including the blue table on page 267.

16. Properties of liquids • Surface tension is an inward force among the molecules in a liquid that brings the molecules on the surface closer together. • Viscosity is a liquid’s resistance to flowing. • Liquids with high viscosity flow slowly (honey). • Liquids with low viscosity flow quickly (water and vinegar). • Complete the “Assess Your Understanding” including the “got it?” on page 268.

17. How do you Describe a Gas? Complete the Figure 5 “Gas” exercise including the blue table on page 269. • As gas particles move in all directions, they spread apart, filling all the space available. • A gas has no definite shape and no definite volume.

18. Volume and Pressure • Volume is the amount of space that matter fills. Because gas particles move and fill all of the space available, the volume of a gas is the same as the volume of its container. • Gas particles constantly collide with one another and push on the walls of their container. The pressure of the gas is the force of its outward push divided by the area of the walls of the container. • Pressure (Pa) = Force (N) / Area (m2)

19. Complete the “do the math!” exercise “calculating pressure” on page 270.Complete the Figure 6 exercise “Gas Pressure” on page 270.

20. Temperature • All particles of matter are constantly moving. The average kinetic energy of the particles in a substance determines the object’s temperature, which is a measure of how hot or cold something is. • The greater the particles’ energy, the faster the particles are moving and the higher the temperature. • Because the particles in a hot air balloon are heated, they have more energy and are able to move around more and spread out. This spreading out causes them to take up more space and be less dense. The lower density causes the hot air balloon to rise. • Complete the “Assess Your Understanding” including the “got it?” on page 271. • Complete the “Review and Assessment” questions #5-9 on page 283.

21. Lesson 3: Changes of State

22. Complete the “My Planet Diary” on page 272.

23. What happens when heat is transferred to a substance? • Thermal Energy: All matter is made up of tiny particles that are always moving, so these particles have kinetic energy. The more kinetic energy the particles have, the hotter the object feels. • Thermal energy is the total kinetic and potential energy of the particles in an object. • A cup of water has less thermal energy than a lake at the same temperature because there are fewer water particles in the cup than in the lake. • Complete the Figure 1 exercise “Thermal Energy” on page 273.

24. Heat: Heat is the transfer of thermal energy from a warmer object to a cooler object. When heat is transferred to a substance, the substance undergoes an increase in temperature, a change of state, or both. • Physical Changes: A physical property is a characteristic of a substance than can be observed without changing it into another substance, without changing the substance itself. • An increase in temperature or a change of state is an example of a physical change; it is the same substance even if it is at a different temperature. • Complete the “Assess Your Understanding” including the “got it?” on page 274.

25. What happens to a solid as it melts? • Particles of a liquid have more thermal energy than particles of the same substance in solid form. • As a gas, the particles have even more thermal energy. • A change from solid to liquid to gas involves an increase in thermal energy. • A change from gas to liquid to solid involves a decrease in thermal energy.

26. Melting • The change in state from a solid to a liquid is called melting. • The temperature a substance melts at is called the melting point. The melting point can sometimes be used to help identify a substance. • In order to melt a substance, you must add thermal energy. This increase in energy causes the molecules in the substance to vibrate faster, raising the temperature. At the substance’s melting point, the particles vibrate so fast that they break free from their fixed positions. The temperature stops increasing; any added energy continues to melt the substance. • Complete the Figure 3 exercise “Melting” on page 275.

27. Freezing • The change of state from liquid to solid is called freezing. • At a liquid’s freezing point, its particles are moving so slowly that they begin to take on fixed positions. When the liquid begins to freeze, the temperature stays at the freezing point until freezing is complete. • The freezing point is the same as the melting point. • Complete the “apply it!”exercise on page 276. • Complete the “Assess Your Understanding” including the “got it?” on page 276.

28. What happens to a substance that becomes a gas? • The change of state from liquid to gas is called vaporization. • Vaporization happens when the particles in a liquid gain enough energy to move independently and form a gas. • There are two types of vaporization: evaporation and boiling.

29. Evaporation and Boiling • Evaporation: Vaporization that takes place only on the surface of a liquid is called evaporation. • An example is a shrinking puddle: the added energy from the sun enables some of the water molecules at the surface of the puddle to evaporate (escape as a gas into the air). • Boiling: Vaporization that takes place both below and at the surface of a liquid is called boiling. • When a liquid boils, vaporized molecules form beneath the surface of the liquid. The bubbles rise, break the surface of the liquid, and escape into the air. • The temperature at which a liquid boils is its boiling point. Complete the “Compare and Contrast” exercise on pg 277.

30. Complete the Figure 4 exercise “Types of Vaporization” on page 277.

31. Condensation • Condensation is the change in state from a gas to a liquid. • Condensation occurs when particles in a gas lose enough thermal energy to form a liquid. • Complete the “Vocabulary” exercise on page 278. • Complete the Figure 5 exercise “Foggy Mirror” on page 278.

32. Complete the “do the math!” exercise on page 278.

33. Sublimation • Sublimation occurs when the surface particles of a solid gain enough energy that they form a gas. • The particles of a solid do not pass through the liquid state as they gain enough energy to move independently and form a gas. • One example is dry ice (solid carbon dioxide). • Complete the Figure 6 exercise “Dry Ice” on page 279. • Complete the “Explore the Essential ?” exercise “The Changing States of Water” on page 280-281. Complete the “Assess Your Understanding” including the “got it?” on page 281. • Complete the “Review and Assessment” questions #10-16 on page 284. • Complete the Florida Benchmark Review questions #1-6 on page 285. This is worth 1 grade and will be graded for accuracy.