1. Chapter IntroductionLesson 1 Discovering Parts of an AtomLesson 2 Protons, Neutrons, and Electrons— How Atoms DifferChapter Wrap-Up
2. What are atoms, andwhat are they made of?
3. What do you think?Before you begin, decide if you agree ordisagree with each of these statements.As you view this presentation, see if youchange your mind about any of thestatements.
4. Do you agree or disagree?1. The earliest model of an atom contained only protons and electrons.2. Air fills most of an atom.3. In the present-day model of the atom, the nucleus of the atom is at the center of an electron cloud.
5. Do you agree or disagree?4. All atoms of the same element have the same number of protons.5. Atoms of one element cannot be changed into atoms of another element.6. Ions form when atoms lose or gain electrons.
6. Discovering Part of an Atom • What is an atom? • How would you describe the size of an atom? • How has the atomic model changed over time?
7. Discovering Part of an Atom • atom • neutron • electron • electron cloud • nucleus • proton
8. Early Ideas About MatterDemocritus (460–370 BC) believed thatmatter is made of small, solid objectscalled atomos, from which the Englishword atom is derived.
9. Early Ideas About Matter (cont.)• Aristotle (384–322 BC) did not believe that empty space exists, but instead believed that all matter is made of fire, water, air, and earth.• Because Aristotle was so influential, his ideas were accepted and Democritus’s ideas about atoms were not studied again for more than 2,000 years.
10. Dalton’s Atomic ModelJohn Dalton combined data from his ownscientific research with data from theresearch of other scientists to propose anew atomic theory.
11. The AtomAn atom is the smallest piece of anelement that still represents that element. What is a copper atom?
12. The Atom (cont.)• Atoms of different elements are different sizes, but all are very, very small.• You cannot see atoms with just your eyes or even with most microscopes. How would you describe the size of an atom?
13. The Atom (cont.)• The 1981 invention of a high-powered microscope, called a scanning tunneling microscope (STM), enabled scientists to see individual atoms for the first time.• Scientists have learned that atoms are not the smallest particles of matter.
14. Following his experiments with cathode raytubes, scientist J.J. Thomson concluded thatcathode rays were made of small, negativelycharged particles which he called electrons.
15. Thomson—Discovering ElectronsAn electron is a particle with one negativecharge (1–). electron from Greek electron, means “amber,” the physical force so called because it first was generated by rubbing amber. Amber is a fossilized substance produced by trees.
16. Thomson—Discovering Electrons (cont.)• Because atoms are neutral, or not electrically charged, Thomson proposed that atoms also must contain a positive charge that balances the negatively charged electrons.• Thomson’s proposed atom was a sphere with a positive charge evenly spread throughout and negatively charged electrons within it.
17. Thomson’s model of the atom contained asphere of positive charge with negativelycharged electrons within it.
18. Rutherford—Discoveringthe NucleusScientist Ernest Rutherford set upexperiments to test Thomson’s atomicmodel and to learn more about whatatoms contain.
19. Rutherford expected the positive alphaparticles to travel straight through the foilwithout changing direction.
20. Some alpha particles traveled in a straightpath, as expected. But some changeddirection, and some bounced straightback.
21. Rutherford—Discoveringthe Nucleus (cont.) Given the results of the gold foil experiment, how do you think an actual atom differs from Thomson’s model?
22. Rutherford—Discoveringthe Nucleus (cont.)• Rutherford concluded that most of an atom’s mass and positive charge is concentrated in a small area in the center of the atom called the nucleus.• Additional research showed that the positive charge in the nucleus was made of positively charged particles called protons.
23. Rutherford—Discoveringthe Nucleus (cont.)• A proton is an atomic particle that has one positive charge (1+).• Negatively charged electrons move in the empty space surrounding the nucleus.
24. Rutherford’s model contains a small, dense,positive nucleus. Tiny, negatively chargedelectrons travel in empty space around thenucleus.
25. Discovering Neutrons• James Chadwick discovered that, in addition to protons, the nucleus also contained neutrons.• A neutron is a neutral particle that exists in the nucleus of an atom.
26. Bohr’s Atomic Model• Niels Bohr proposed that electrons move in circular orbits, or energy levels, around the nucleus.• Electrons closer to the nucleus have less energy than electrons farther away from the nucleus.
27. Bohr’s Atomic Model (cont.)• More research showed that, although electrons have specific amounts of energy, energy levels are not arranged in circular orbits.• When an electron moves from a higher energy level to a lower energy level, energy is released—sometimes as visible light.
28. In Bohr’s model of the atom, electronsmove in circular orbits around the atom.
29. Bohr’s Atomic Model (cont.) How did Bohr’s model of the atom differ from Rutherford’s?
30. The Modern Atomic Model• In the modern atomic model, electrons form an electron cloud.• An electron cloud is an area around an atomic nucleus where an electron is most likely to be.
31. In this atom, electrons are more likelyto be found closer to the nucleus thanfarther away.
32. The Modern Atomic Model (cont.) How has the model of the atom changed over time?
33. Quarks• Protons and neutrons are made of smaller particles called quarks.• Scientists theorize that there are six types of quarks: up, down, charm, strange, top, and bottom.• Protons are made of two up quarks and one down quark.
34. Quarks (cont.)• Neutrons are made of two down quarks and one up quark.• The current atomic model might change with the invention of new technology that aids the discovery of new information.
35. • If you were to divide an element into smaller and smaller pieces, the smallest piece would be an atom.• Atoms are so small that they can be seen only by using very powerful microscopes.
36. • Scientists now know that atoms contain a dense, positive nucleus surrounded by an electron cloud.
37. Which term describes a particlewith one negative charge?A. atomB. electronC. nucleusD. proton
38. Whose model of the atomcontained a sphere of positivecharge with negatively chargedelectrons within it?A. DaltonB. DemocritusC. RutherfordD. Thomson
39. Which term refers to an areaaround an atomic nucleus wherean electron is most likely to be?A. electron cloudB. neutronC. nucleusD. proton
40. Do you agree or disagree?1. The earliest model of an atom contained only protons and electrons.2. Air fills most of an atom.3. In the present-day model of the atom, the nucleus of the atom is at the center of an electron cloud.
41. Protons, Neutrons, andElectrons—How Atoms Differ• What happens during nuclear decay?• How does a neutral atom change when its number of protons, electrons, or neutrons changes?
42. Protons, Neutrons, andElectrons—How Atoms Differ• atomic number • radioactive• isotope • nuclear decay• mass number • ion• average atomic mass
43. The Parts of the Atom• The mass of electrons is much smaller than the mass of protons or neutrons.• Most of the mass of an atom is found in the nucleus.
44. Different Elements—DifferentNumbers of Protons• The number of protons in an atom of an element is the element’s atomic number.• The atomic number is the whole number listed with each element on the periodic table.• Atoms of different elements contain different numbers of protons.
45. Different elements have different atomicnumbers.
46. Different Elements—DifferentNumbers of Protons (cont.)• Neutral atoms of different elements also have different numbers of electrons.• In a neutral atom, the number of electrons equals the number of protons; therefore, the number of positive charges equals the number of negative charges.
47. Neutrons and Isotopes• Atoms of the same element can have different numbers of neutrons.• Isotopes are atoms of the same element that have different numbers of neutrons.• Most elements have several isotopes.
48. Neutrons and Isotopes (cont.) isotope from Greek isos, means “equal”; and topos, means “place”
49. Neutrons and Isotopes (cont.)• The mass number of an atom is the sum of the number of protons and neutrons in an atom. Mass number = number of protons + number of neutrons• An isotope is often written with the element name followed by the mass number.
50. Neutrons and Isotopes (cont.)The average atomicmass of an element isthe average mass of theelement’s isotopes,weighted according tothe abundance of eachisotope.
51. Radioactivity• Marie Curie called elements that spontaneously emit radiation radioactive.• Henri Becquerel and Pierre and Marie Curie discovered that the radiation released by uranium was made of energy and particles.
52. Radioactivity (cont.)• This radiation came from the nuclei of the uranium atoms.• When uranium releases radiation, it changes to a different element.
53. Radioactivity (cont.)• Nuclear decay is a process that occurs when an unstable atomic nucleus changes into another more stable nucleus by emitting radiation.• Nuclear decay can produce three different types of radiation—alpha particles, beta particles, and gamma rays.
54. An alpha particle is made of two protons andtwo neutrons. When an atom releases analpha particle, its atomic number decreasesby two.
55. When beta decay occurs, a neutron changesinto a proton and a high-energy electroncalled a beta particle. The atomic numberof an atom increases by one because it hasgained a proton.
56. Because gamma rays do not containparticles, the release of gamma rays doesnot change one element into anotherelement.
57. Radioactivity (cont.) What happens during radioactive decay?
58. Radioactivity (cont.)• The energy released by radioactive decay can be both harmful and beneficial to humans.• Radiation therapy can be beneficial to humans by destroying harmful cells such as cancer cells.
59. Ions—Gaining or Losing Electrons• An ion is an atom that is no longer neutral because it has gained or lost electrons.• An ion can be positively or negatively charged depending on whether it has lost or gained electrons.
60. • When a neutral atom loses one or more electrons, it has more protons than electrons and as a result, has a positive charge.• An atom with a positive charge is called a positive ion.
61. • When a neutral atom gains one or more electrons, it now has more electrons than protons and as a result, has a negative charge.• An atom with a negative charge is called a negative ion.
62. Ions—Gaining or Losing Electrons (cont.) How does a neutral atom change when its number of protons or electrons changes?
63. • Different elements contain different numbers of protons.
64. • Two isotopes of a given element contain different numbers of neutrons.
65. • When a neutral atom gains or loses an electron, it becomes an ion.
66. Where is most of the mass ofan atom found?A. electronsB. neutronsC. nucleusD. protons
67. Which term refers to the sumof the number of protons andneutrons in an atom?A. atomic numberB. average atomic massC. isotopeD. mass number
68. What term did Marie Curie useto describe elements thatspontaneously emit radiation?A. ionB. isotopesC. nuclear decayD. radioactive
69. Do you agree or disagree?4. All atoms of the same element have the same number of protons.5. Atoms of one element cannot be changed into atoms of another element.6. Ions form when atoms lose or gain electrons.
70. Key Concept SummaryInteractive Concept MapChapter ReviewStandardized Test Practice
71. An atom is thesmallest unit of anelement and is mademostly of empty space.It contains a tinynucleus surroundedby an electron cloud.
72. Lesson 1: Discovering Parts of the Atom• If you were to divide an element into smaller and smaller pieces, the smallest piece would be an atom.• Atoms are so small that they can be seen only by powerful scanning microscopes.• The first model of the atom was a solid sphere. Now, scientists know that an atom contains a dense positive nucleus surrounded by an electron cloud.
73. Lesson 2: Protons, Neutrons, andElectrons—How Atoms Differ• Nuclear decay occurs when an unstable atomic nucleus changes into another more stable nucleus by emitting radiation.• Different elements contain different numbers of protons. Two isotopes of the same element contain different numbers of neutrons. When a neutral atom gains or loses an electron, it becomes an ion.
74. Which term describes a neutralparticle that exists in the nucleusof an atom?A. atomB. electronC. neutronD. proton
75. Who discovered that, in additionto protons, the nucleus alsocontained neutrons?A. ThomsonB. RutherfordC. ChadwickD. Bohr
76. Protons and neutrons are madeof smaller particles called what?A. electron cloudB. isotopeC. nucleusD. quarks
77. Which term refers to the processthat occurs when an unstableatomic nucleus changes intoanother more stable nucleusby emitting radiation?A. radiationB. radioactivityC. nuclear decayD. radiation therapy
78. Which describes an atom with apositive charge?A. positive ionB. negative ionC. isotopeD. quarks
79. Which term refers to the smallestpiece of an element that stillrepresents that element?A. quarkB. nucleusC. electronD. atom
80. Who concluded that most of anatom’s mass and positive chargeis concentrated in the nucleus?A. AristotleB. BohrC. ChadwickD. Rutherford
81. Which is an atomic particle thathas one positive charge?A. protonB. nucleusC. neutronD. electron
82. Which term refers to an atom thatis no longer neutral because ithas gained or lost electrons?A. ionB. isotopeC. neutronD. proton
83. Which refers to the average massof an element’s isotopes,weighted according to theabundance of each isotope?A. atomic numberB. mass numberC. relative massD. average atomic mass