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2. Resources Bellringers Chapter Presentation Transparencies Standardized Test Prep Image and Math Focus Bank CNN Videos Visual Concepts

3. Introduction to Atoms Chapter 11 Table of Contents Section 1 Development of the Atomic Theory Section 2 The Atom

4. Section1 Development of the Atomic Theory Chapter 11 Bellringer The following is a quote by Democritus (c. 460–c. 370 bce). Paraphrase this quote in your own words in your science journal. “Color exists by convention, sweet by convention, bitter by convention; in reality nothing exists but atoms and the void.” What do you know about Democritus? And why are his thoughts important?

5. Section1 Development of the Atomic Theory Chapter 11 Objectives • Describesome of the experiments that led to the current atomic theory. • Compare the different models of the atom. • Explain how the atomic theory has changed as scientists have discovered new information about the atom.

6. Section1 Development of the Atomic Theory Chapter 11 The Beginning of the Atomic Theory • What Is an Element?Around 440 BCE, a Greek philosopher named Democritus thought that you would eventually end up with a particle that could not be cut. He called this particle an atom. • From Aristotle to Modern ScienceAristotle, another Greek philosopher, disagreed with Democritus’s ideas. He believed that you would never end up with a particle that could not be cut.

7. Section1 Development of the Atomic Theory Chapter 11 The Beginning of the Atomic Theory, continued • From Aristotle to Modern ScienceDemocritus was right, though: Matter is made of particles, which we call atoms. An atom is the smallest particle into which an element can be divided and still be the same substance.

8. Section1 Development of the Atomic Theory Chapter 11 Dalton’s Atomic Theory Based on Experiments • Dalton’s Atomic TheoryJohn Dalton published his atomic theory in 1803. His theory stated that (#1) all substances are made of atoms. (#2) Atoms are small particles that cannot be created, divided, or destroyed. (#3) Atoms of the same element are exactly alike, and atoms of different elements are different. (#4) Atoms join with other atoms to make new substances. • Not Quite Correct The atomic theory was then changed to describe the atom more correctly.

9. Section1 Development of the Atomic Theory Chapter 11 Thomson’s Discovery of Electrons • Negatively Charged ParticlesThomson experimented with a cathode-ray tube like the one shown on the next slide. Thomson discovered negatively charged particles that are now known as electrons. • Like Plums in PuddingAfter learning that atoms contain electrons, Thomson proposed a new model of the atom. Thomson thought that electrons were mixed throughout an atom, like plums in a pudding.

10. Section1 Development of the Atomic Theory Chapter 11

11. Section1 Development of the Atomic Theory Chapter 11 Rutherford’s Atomic “Shooting Gallery” • Negatively Charged ParticlesIn 1909, Ernest Rutherford aimed a beam of small, positively charged particles at a thin sheet of gold foil. The next slide shows his experiment. • Surprising ResultsRutherford expected the particles to pass right through the gold in a straight line. To Rutherford’s great surprise, some of the particles were deflected.

12. Section1 Development of the Atomic Theory Chapter 11

13. Section1 Development of the Atomic Theory Chapter 11 Where Are the Electrons? • Far from the NucleusRutherford proposed that in the center of the atom is a tiny, positively charged part called the nucleus. • Bohr’s Electron LevelsIn 1913, Niels Bohr proposed that electrons move around the nucleus in certain paths, or energy levels.

14. Section1 Development of the Atomic Theory Chapter 11 Where Are the Electrons?, continued • The Modern Atomic TheoryAccording to the current theory, there are regions inside the atom where electrons are likely to found. These regions are called electron clouds.

15. Section1 Development of the Atomic Theory Chapter 11 Comparing Models of the Atom Click below to watch the Visual Concept. You may stop the video at any time by pressing the Esc key. Visual Concept

16. Section2 The Atom Chapter 11 Bellringer Answer the following question:An atom is the smallest particle into which an element can be divided and still be that element. Now that scientists have learned that an atom is made up of even smaller particles, is this definition still accurate? Explain your answer in yourscience journal.

17. Section2 The Atom Chapter 11 Objectives • Describe the size of an atom. • Namethe parts of an atom. • Describe the relationship between numbers of protons and neutrons and atomic number.

18. Section2 The Atom Chapter 11 Objectives, continued • State how isotopes differ. • Calculate atomic masses. • Describe the forces within an atom.

19. Section2 The Atom Chapter 11 How Small Is an Atom? • Three One-Hundred-Millionths of a Centimeter! Scientists know that aluminum is made of average-sized atoms. An aluminum atom has a diameter of about 0.00000003 cm.

20. Section2 The Atom Chapter 11 What Is an Atom Made Of? • The NucleusProtons are positively charged particles in the nucleus.Neutrons are the particles of the nucleus that have no electrical charge. • Outside the Nucleus Electrons are the negatively charged particles in atoms.Electrons are found around the nucleus within electron clouds. All the structures of the atom can be seen on the next slide.

21. Section2 The Atom Chapter 11

22. Section2 The Atom Chapter 11 How Do Atoms of Different Elements Differ? • Starting SimplyThe hydrogen atom has one proton and one electron. • Now for Some NeutronsThe helium atom has two protons, two neutrons, and two electrons.

23. Section2 The Atom Chapter 11 How Do Atoms of Different Elements Differ? • Building Bigger AtomsFor bigger atoms, simply add protons, neutrons, and electrons. • Protons and Atomic NumberThe number of protons in the nucleus of an atom is the atomic number of that atom. All atoms of an element have the same atomic number.

24. Section2 The Atom Chapter 11 Isotopes • Isotopesare atoms that have the same number of protons but have different numbers of neutrons.

25. Section2 The Atom Chapter 11 Isotopes, continued • Properties of IsotopesAn unstable atom is an atom with a nucleus that will change over time. This type of isotope is radioactive. • Telling Isotopes ApartYou can identify each isotope of an element by its mass number. The mass number is the sum of the protons and neutrons in an atom.

26. Section2 The Atom Chapter 11 Isotopes, continued

27. Section2 The Atom Chapter 11 Isotopes, continued • Naming IsotopesTo identify a specific isotope of an element, write the name of the element followed by a hyphen and the mass number of the isotope. • Calculating the Mass of an ElementThe atomic mass of an element is the weighted average of the masses of all the naturally occurring isotopes of that element.

28. Section2 The Atom Chapter 11

29. Section2 The Atom Chapter 11 Forces in Atoms • Four Basic ForcesFour basic forces are at work everywhere, even within the atom. These forces are gravitational force, electromagnetic force, strong force, and weak force. • These forces work together to give an atom its structure and properties.

30. Section2 The Atom Chapter 11

31. Introduction to Atoms Chapter 11 Concept Map Use the terms below to complete the concept map on the next slide.

32. Concept Map Chapter 11

33. Concept Map Chapter 11

34. End of Chapter 11 Show

35. Standardized Test Preparation Chapter 11 Reading Read each of the passages. Then, answer the questions that follow each passage.

36. Standardized Test Preparation Chapter 11 Passage 1In the Bohr model of the atom, electrons can be found only in certain energy levels. Electrons “jump” from one level to the next level without passing through any of the regions in between. When an electron moves from one level to another, it gains or loses energy, depending on the direction of its jump. Bohr’s model explained an unusual event. When electric charges pass through atoms of a gaseous element, the gas produces a glowing light, like in a neon sign. Continued on the next slide

37. Standardized Test Preparation Chapter 11 Passage 1, continuedIf this light is passed through a prism, a pattern of lines appears, each line having a different color. The pattern depends on the element—neon has one pattern, and helium has another. In Bohr’s model, the lines are caused by electron jumps from higher to lower energy levels. Because only certain jumps are possible, electrons release energy only in certain quantities. These “packets” of energy produce the lines that are seen.

38. Standardized Test Preparation Chapter 11 1. In the Bohr model of the atom, what limitation is placed on electrons? A the number of electrons in an atom B the electrons’ being found only in certain energy levels C the size of electrons D the speed of electrons

39. Standardized Test Preparation Chapter 11 1. In the Bohr model of the atom, what limitation is placed on electrons? A the number of electrons in an atom B the electrons’ being found only in certain energy levels C the size of electrons D the speed of electrons

40. Standardized Test Preparation Chapter 11 2. What causes the colored lines that appear when the light from a gas is passed through a prism? Fpackets of energy released by electron jumps Gelectrons changing color Hatoms of the gas exchanging electrons IThere is not enough information to determine the answer.

41. Standardized Test Preparation Chapter 11 2. What causes the colored lines that appear when the light from a gas is passed through a prism? F packets of energy released by electron jumps Gelectrons changing color Hatoms of the gas exchanging electrons IThere is not enough information to determine the answer.

42. Standardized Test Preparation Chapter 11 Passage 2No one has ever seen a living dinosaur, but scientists have determined the appearance of Tyrannosaurus rex by studying fossilized skeletons. Scientists theorize that these extinct creatures had big hind legs, small front legs, a long, whip-like tail, and a mouth full of dagger-shaped teeth. However, theories of how T. rex walked have been harder to develop. For many years, most scientists thought that T. rex plodded slowly like a big, lazy lizard. Continued on the next slide

43. Standardized Test Preparation Chapter 11 Passage 2, continuedHowever, after studying well-preserved dinosaur tracks and noticing skeletal similarities between certain dinosaur fossils and living creatures like the ostrich, many scientists now theorize that T. rex could turn on the speed. Some scientists estimate that T. rex had bursts of speed of 32 km/h (20 mi/h)!

44. Standardized Test Preparation Chapter 11 1.According to this passage, where does most of what we know about the appearance of Tyrannosaurus rex come from? Afossilized skeletons Bdinosaur tracks Cliving organisms such as the ostrich Dliving specimens of T. rex

45. Standardized Test Preparation Chapter 11 1.According to this passage, where does most of what we know about the appearance of Tyrannosaurus rex come from? A fossilized skeletons Bdinosaur tracks Cliving organisms such as the ostrich Dliving specimens of T. rex

46. Chapter 11 Standardized Test Preparation 2. How did scientists conclude that T. rex could probably move very quickly? FThey measured the speed at which it could run. GThey compared fossilized T. rex tracks with T. rex skeletons. HThey studied dinosaur tracks and noted similarities between ostrich skeletons and T. rex skeletons. IThey measured the speed at which ostriches could run.

47. Chapter 11 Standardized Test Preparation 2. How did scientists conclude that T. rex could probably move very quickly? FThey measured the speed at which it could run. GThey compared fossilized T. rex tracks with T. rex skeletons. H They studied dinosaur tracks and noted similarities between ostrich skeletons and T. rex skeletons. IThey measured the speed at which ostriches could run.

48. Chapter 11 Standardized Test Preparation Interpreting Graphics Use the diagram of an atom below to answer the questions that follow.

49. Chapter 11 Standardized Test Preparation 1. The black circles in the center of the model represent neutrons. What do the white circles in the center represent? Aelectrons Bprotons Cnuclei Datoms

50. Chapter 11 Standardized Test Preparation 1. The black circles in the center of the model represent neutrons. What do the white circles in the center represent? Aelectrons Bprotons Cnuclei Datoms