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Section 2.1 Atoms and Their Structures
Section 2.2 Electrons in Atoms
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3. Atoms and Their Structures
Relate historic experiments to the development of the modern model of the atom.
Illustrate the modern model of an atom.
Interpret the information available in an element block of the periodic table.
Section 2.1

4. Atoms and Their Structures
energy: the capacity to do work
Section 2.1

5. Atoms and Their Structures
atomic theory
law of definite proportions
hypothesis
experiment
theory
scientific method
scientific law
electron
proton
isotope
neutron
nucleus
atomic number
mass number
isotope
atomic mass unit
An atom is made of a nucleus containing protons and neutrons; electrons move around the nucleus.
Section 2.1

6. Early Ideas About Matter
Greek philosophers thought that matter was composed of four elements: earth, water, air, and fire.
Section 2.1

7. Early Ideas About Matter (cont.)
Democritus (460–370 B.C.) first proposed that the world is made up of empty space and atoms, the smallest particle of a given type of matter.
The idea that matter is made up of fundamental particles called atoms is known as the atomic theory of matter.
Section 2.1

8. Modern Atomic Theory
Antoine Lavoisier concluded that when a chemical reaction occurs, matter is neither created nor destroyed but only changed. This conclusion became known as the law of conservation of matter.
Section 2.1

9. Modern Atomic Theory (cont.)
In 1799, Joseph Proust proposed the law of definite proportions, or the principle that the elements that comprise a compound are always in a certain proportion by mass.
Composition of iron sulfide
Section 2.1

10. Modern Atomic Theory (cont.)
Dalton’s Atomic Theory
All matter is made of atoms.
Atoms are indestructible and indivisible.
All atoms of one element are exactly alike, but they are different from atoms of other elements.
Section 2.1

11. Modern Atomic Theory (cont.)
In natural processes, atoms are not destroyed; they are recycled.
Section 2.1

12. Hypotheses, Theories, and Laws
A hypothesis is a prediction that can be tested to explain observations.
An experiment is an investigation with a control designed to test a hypothesis.
A theory is an explanation based on many observations and supported by the results of many investigations.
Section 2.1

13. Hypotheses, Theories, and Laws (cont.)
The systematic approach scientists use to answer questions and solve problems is called the scientific method.
Section 2.1

14. Hypotheses, Theories, and Laws (cont.)
A scientific law is a fact of nature that is observed so often that it becomes accepted as truth.
The Sun rising in the east each morning is a scientific law.
Section 2.1

15. The Discovery of Atomic Structure
From Thomson’s experiments, scientists concluded that atoms were composed of electrically-charged particles.
An electron is a negatively-charged particle.
A proton is a positive-charged subatomic particle.
A neutron is a subatomic particle that has a mass equal to a proton by no electrical charge.
Section 2.1

16. The Discovery of Atomic Structure (cont.)
Atoms of an element that are chemically alike but differ in mass are called isotopes.
Section 2.1

17. The Discovery of Atomic Structure (cont.)
Scientists proposed different atomic models.
Section 2.1

18. The Discovery of Atomic Structure (cont.)
Rutherford’s gold foil experiment revealed an atomic arrangement far different from earlier models.
Section 2.1

19. The Discovery of Atomic Structure (cont.)
Rutherford’s team proposed a new model of the atom that included a nucleus, a small dense, positively-charged central core.
Rutherford’s Model
Modern Model
Section 2.1

20. Atomic Numbers
The atomic number refers to the number of protons in the nucleus of an atom.
The mass number is sum of the protons and neutrons in the nucleus of an atom.
Isotopes of an element have different mass numbers because they have different numbers of neutrons.
Section 2.1

21. Atomic Numbers (cont.)
Section 2.1

22. Atomic Mass
To easily compare the masses of individual atoms, scientists devised a different unit of mass, the atomic mass unit (u), which is approximately the mass of a single proton or neutron.
Section 2.1

23. Atomic Mass (cont.)
Section 2.1

24. Atomic Mass (cont.)
Each box of the periodic table contains several pieces of information about an element.
Section 2.1

25. Atomic Mass (cont.)
To calculate the weighted average atomic mass, you first need to calculate the mass contribution of each isotope.
Naturally Occurring Isotopes of Chlorine
Section 2.1

26. Section Assessment
The idea that matter is made up of fundamental particles called atoms is known as ___.
A. the law of conservation of matter
B. the law of conservation of mass
C. the atomic theory of mass
D. the atomic theory of matter
Section 2.1

27. Section Assessment
Isotopes of an element have different mass numbers because they have different numbers of ___.
A. protons
B. electrons
C. neutrons
D. nuclei
Section 2.1

28. End of Section 2.1

29. Electrons in Atoms Relate the electron to modern atomic theory.
Compare electron energy levels in an atom.
Illustrate valence electrons by Lewis electron dot structures.
Section 2.2

30. Electrons in Atoms atom: smallest particle of a given type of matter
Section 2.2

31. Electrons in Atoms electromagnetic spectrum emission spectrum
energy level
electron cloud
valence electron
Lewis dot diagram
Each element has a unique arrangement of electrons.
Section 2.2

32. Electrons in Motion
Niels Bohr (1885–1962) proposed that electrons must have enough energy to keep them in constant motion around the nucleus.
Electrons occupy orbits of only certain amounts of energy.
Section 2.2

33. The Electromagnetic Spectrum
High-voltage electricity or electromagnetic radiation, or radiant energy, can increase the energy of an electron.
Electromagnetic radiation travels in the form of waves that have both electric and magnetic properties.
Section 2.2

34. The Electromagnetic Spectrum (cont.)
The electromagnetic spectrum is the whole range of electromagnetic radiation.
radio waves
radiant energy
visible light
Higher-frequency electromagnetic waves have higher energy than lower-frequency waves.
Section 2.2

35. The Electromagnetic Spectrum (cont.)
Section 2.2

36. Electrons and Light
Each element emits a different emission spectrum, or a spectrum of light released from excited atoms of the element.
Section 2.2

37. Electrons and Light (cont.)
Because electrons can have only certain amounts of energy, they can move around the nucleus only at distances that correspond to those amounts of energy.
Section 2.2

38. Electrons and Light (cont.)
The regions of space in which electrons can move about the nucleus of an atom are called energy levels.
Section 2.2

39. The Electron Cloud Model
The electron cloud is the space around the nucleus of an atom where the atom’s electrons are most likely to be found.
Section 2.2

40. The Electron Cloud Model (cont.)
Each energy level can hold a limited number of electrons.
First energy level—2 electrons
Second energy level—8 electrons
Third energy level—18 electrons
Section 2.2

41. The Electron Cloud Model (cont.)
The electrons in the outermost energy level are called valence electrons.
Section 2.2

42. The Electron Cloud Model (cont.)
Many of the chemical and physical properties of an element are directly related to the number and arrangement of valence electrons.
Section 2.2

43. The Electron Cloud Model (cont.)
A Lewis dot diagram is a diagram where dots are placed around the chemical symbol of an element to illustrate the valence electrons.
Section 2.2

44. Section Assessment
The first energy level of an atom holds a maximum of ___ electrons.
A. one
B. two
C. four
D. eight
Section 2.2

45. Section Assessment
In a Lewis dot diagram, each dot represents a(n) ___.
A. neutron
B. proton
C. electron
D. valence electron
Section 2.2

46. End of Section 2.2

47. Standardized Test Practice Image Bank Concepts in Motion
Chemistry Online
Study Guide
Chapter Assessment
Standardized Test Practice
Image Bank
Concepts in Motion
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48. Scientists make hypotheses based on observation.
Key Concepts
Scientists make hypotheses based on observation.
Dalton’s atomic theory states that matter is made up of indestructible atoms.
Experiments in the late nineteenth and early twentieth centuries revealed that the mass of an atom is concentrated in a tiny nucleus.
The number of protons in an atom’s nucleus is called the atomic number and equals the number of electrons in the atom.
Atoms of the same element always have the same number of protons and electrons.
Study Guide 1

49. Electrons move around an atom’s nucleus in specific energy levels.
Key Concepts
Electrons move around an atom’s nucleus in specific energy levels.
Energy levels are spherical regions in which electrons are likely to be found.
The greater the energy of the level, the farther from the nucleus the level is located.
Electrons can absorb energy and move to a higher energy level.
Lewis dot diagrams can be used to represent the valence electrons in a given atom.
Study Guide 2

50. Early Greek philosophers proposed that matter was a combination of what four fundamental elements?
A. air, fire, wind, earth
B. fire, air, earth, water
C. hot, dry, cold, wet
D. water, wind, fire, ice
Chapter Assessment 1

51. What is an explanation based on many observations and supported by the results of many investigations?
A. theory
B. experiment
C. hypothesis
D. scientific law
Chapter Assessment 2

52. What is the systemic approach scientists use to answer questions and solve problems?
A. experiment
B. hypothesis
C. scientific law
D. scientific method
Chapter Assessment 3

53. What is the distance between corresponding points on two consecutive waves?
A. spectrum
B. rate
C. wavelength
D. frequency
Chapter Assessment 4

54. Atoms in group 2 of the periodic table have how many valence electrons?
Chapter Assessment 5

55. The mass of a proton is ___ the mass of an electron. A. greater than
B. less than
C. equal to
STP 1

56. The mass of a neutron is ___ the mass of a proton. A. greater than
B. less than
C. equal to
STP 2

57. The atomic number determines the identity of an element, as well as many of its chemical and physical properties.
A. true
B. false
STP 3

58. What kind of properties do electromagnetic radiation waves have?
A. electric
B. magnetic
C. nuclear
D. A and B
STP 4

59. The energy of higher-frequency electromagnetic waves is ____ lower-frequency waves.
A. higher than
B. lower than
C. the same as
STP 5

60. Click on an image to enlarge.
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61. Click on an image to enlarge.
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62. IB 1

63. IB 2

64. IB 3

65. IB 4

66. IB 5

67. IB 6

68. IB 7

69. Rutherford’s Model
Modern Model
IB 8

70. IB 9

71. IB 10

72. IB 11

73. Naturally Occurring Isotopes of Chlorine
IB 12

74. IB 13

75. IB 14

76. IB 15

77. IB 16

78. IB 17

79. IB 18

80. IB 19

81. IB 20

82. IB 21

83. Table 2.1 Particles of an Atom Figure 2.4 The Nitrogen Cycle
Figure 2.9 Rutherford’s Experiment
Figure 2.20 The Emission Spectrum
Figure 2.21 Energy Levels in an Atom
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