1. Chapter 3 Table of Contents
Atoms: The Building Blocks of Matter
Chapter 3
Table of Contents
Section 1 The Atom: From Philosophical Idea to Scientific Theory
Section 2 The Structure of the Atom
Section 3 Counting Atoms

2. DO NOW
In the 5th century BCE a Greek philosopher named Leucippus and his student, Democritis, stated, “All matter is made up of particles that can be divided called atoms.”
What do you think atoms are?
Unit 1 • Investigation III 2

3. Objectives Introduction to the atom and its models
Investigate various historical models of the atom
Definition of atom, size and structures

4. All matter is made up of atoms.
Atoms are extremely small particles, which cannot be seen, even with microscopes.
All matter is made up of atoms.
Scientists have created models to describe atoms. Models are similar to theories, but often include a picture or physical representation.
Unit 1 • Investigation III 4

5. (cont.)
Five Models of the Atom
Unit 1 • Investigation III 5

6. Models / Scientists Dalton --------- B J.J Thompson ---------- D
Rutherford or Nuclear A
Bohr E
Quantum C

7. Models
Its possible to remove a negatively charged particle from an atom using electrical forces. (J. J. Thompson, 1897)
If a tiny particle is shot into a middle of an atom. It hits something dense in the center and bounces back in the direction it came from. If a tiny particle is shot into the edges of the atom, it goes through. Most tiny particles shot in an atom will go through. (Rutherford,1911)
The farther away from the center of an atom the negatively charged particles, are the easier they are to remove. (Bohr, 1913)

8. An atom is mostly empty space.
The rest consists of a nucleus, which is located in the very center of the atom, and electrons, which are located around the nucleus.
The nucleus is very small
Unit 1 • Investigation III 8

9. A neutron is a neutral particle with no charge on it.
The nucleus is also very dense and consists of two types of particles— neutrons and protons.
A neutron is a neutral particle with no charge on it.
A proton is a positively charged particle.
Tightly bound together, neutrons and protons make a positively charged nucleus.
Unit 1 • Investigation III 9

10. Section 1 The Atom: From Philosophical Idea to Scientific Theory
Chapter 3
Objectives
Explain the law of conservation of mass, the law of definite proportions, and the law of multiple proportions.
Summarize the five essential points of Dalton’s atomic theory.
Explain the relationship between Dalton’s atomic theory and the law of conservation of mass, the law of definite proportions, and the law of multiple proportions. The transformation of a substance or substances into one or more new substances is known as a chemical reaction.
Law of conservation of mass: mass is neither created nor destroyed during ordinary chemical reactions or physical changes

11. Foundations of Atomic Theory
Section 1 The Atom: From Philosophical Idea to Scientific Theory
Chapter 3
Foundations of Atomic Theory
The transformation of a substance or substances into one or more new substances is known as a chemical reaction.
Law of conservation of mass: mass is neither created nor destroyed during ordinary chemical reactions or physical changes

12. Visual Concepts
Chapter 3
Chemical Reaction

13. Foundations of Atomic Theory
Section 1 The Atom: From Philosophical Idea to Scientific Theory
Chapter 3
Foundations of Atomic Theory
Law of definite proportions: a chemical compound contains the same elements in exactly the same proportions by mass regardless of the size of the sample or source of the compound
Law of multiple proportions: if two or more different compounds are composed of the same two elements, then the ratio of the masses of the second element combined with a certain mass of the first element is always a ratio of small whole numbers

14. Law of Conservation of Mass
Section 1 The Atom: From Philosophical Idea to Scientific Theory
Chapter 3
Law of Conservation of Mass

15. Law of Multiple Proportions
Section 1 The Atom: From Philosophical Idea to Scientific Theory
Chapter 3
Law of Multiple Proportions

16. Dalton’s Atomic Theory
Section 1 The Atom: From Philosophical Idea to Scientific Theory
Chapter 3
Dalton’s Atomic Theory
All matter is composed of extremely small particles called atoms.
Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties.
Atoms cannot be subdivided, created, or destroyed.

17. Dalton’s Atomic Theory
Section 1 The Atom: From Philosophical Idea to Scientific Theory
Chapter 3
Dalton’s Atomic Theory
Atoms of different elements combine in simple whole- number ratios to form chemical compounds.
In chemical reactions, atoms are combined, separated, or rearranged.

18. Modern Atomic Theory Chapter 3
Section 1 The Atom: From Philosophical Idea to Scientific Theory
Chapter 3
Modern Atomic Theory
Not all aspects of Dalton’s atomic theory have proven to be correct. We now know that:
Atoms are divisible into even smaller particles.
A given element can have atoms with different masses.
Some important concepts remain unchanged.
All matter is composed of atoms.
Atoms of any one element differ in properties from atoms of another element.

19. Lesson Starter Chapter 3
Section 2 The Structure of the Atom
Chapter 3
Lesson Starter
Even though the two shapes look different, the characteristics of the various parts that compose them are the same.
The same is true with the atom.
Though atoms of different elements display different properties, isolated subatomic particles have the same properties.

20. Section 2 The Structure of the Atom
Chapter 3
Objectives
Summarize the observed properties of cathode rays that led to the discovery of the electron.
Summarize the experiment carried out by Rutherford and his co-workers that led to the discovery of the nucleus.
List the properties of protons, neutrons, and electrons.
Define atom.

21. The Structure of the Atom
Section 2 The Structure of the Atom
Chapter 3
The Structure of the Atom
An atom is the smallest particle of an element that retains the chemical properties of that element.
The nucleus is a very small region located at the center of an atom.
The nucleus is made up of at least one positively charged particle called a proton and usually one or more neutral particles called neutrons.

22. The Structure of the Atom
Section 2 The Structure of the Atom
Chapter 3
The Structure of the Atom
Surrounding the nucleus is a region occupied by negatively charged particles called electrons.
Protons, neutrons, and electrons are often referred to as subatomic particles.

23. Visual Concepts
Chapter 3
Atom

24. Properties of Subatomic Particles
Section 2 The Structure of the Atom
Chapter 3
Properties of Subatomic Particles

25. Discovery of the Electron
Section 2 The Structure of the Atom
Chapter 3
Discovery of the Electron
Cathode Rays and Electrons
Experiments in the late 1800s showed that cathode rays were composed of negatively charged particles.
These particles were named electrons.

26. Discovery of the Electron
Section 2 The Structure of the Atom
Chapter 3
Discovery of the Electron
Charge and Mass of the Electron
Joseph John Thomson’s cathode-ray tube experiments measured the charge-to-mass ratio of an electron.
Robert A. Millikan’s oil drop experiment measured the charge of an electron.
With this information, scientists were able to determine the mass of an electron.

27. Discovery of the Electron, continued
Section 2 The Structure of the Atom
Chapter 3
Discovery of the Electron, continued

28. Discovery of the Atomic Nucleus
Section 2 The Structure of the Atom
Chapter 3
Discovery of the Atomic Nucleus
More detail of the atom’s structure was provided in 1911 by Ernest Rutherford and his associates Hans Geiger and Ernest Marsden.
The results of their gold foil experiment led to the discovery of a very densely packed bundle of matter with a positive electric charge.
Rutherford called this positive bundle of matter the nucleus.

29. Section 2 The Structure of the Atom
Chapter 3
Gold Foil Experiment

30. Gold Foil Experiment on the Atomic Level
Section 2 The Structure of the Atom
Chapter 3
Gold Foil Experiment on the Atomic Level

31. Composition of the Atomic Nucleus
Section 2 The Structure of the Atom
Chapter 3
Composition of the Atomic Nucleus
Except for the nucleus of the simplest type of hydrogen atom, all atomic nuclei are made of protons and neutrons.
A proton has a positive charge equal in magnitude to the negative charge of an electron.
Atoms are electrically neutral because they contain equal numbers of protons and electrons.
A neutron is electrically neutral.

32. Composition of the Atomic Nucleus
Section 2 The Structure of the Atom
Chapter 3
Composition of the Atomic Nucleus
The nuclei of atoms of different elements differ in their number of protons and therefore in the amount of positive charge they possess.
Thus, the number of protons determines that atom’s identity.

33. Chapter 3 Forces in the Nucleus
Section 2 The Structure of the Atom
Chapter 3
Forces in the Nucleus
When two protons are extremely close to each other, there is a strong attraction between them.
A similar attraction exists when neutrons are very close to each other or when protons and neutrons are very close together.
The short-range proton-neutron, proton-proton, and neutron-neutron forces that hold the nuclear particles together are referred to as nuclear forces.

34. The Sizes of Atoms Chapter 3
Section 2 The Structure of the Atom
Chapter 3
The Sizes of Atoms
The radius of an atom is the distance from the center of the nucleus to the outer portion of its electron cloud.
Because atomic radii are so small, they are expressed using a unit that is more convenient for the sizes of atoms.
This unit is the picometer, pm.

35. Lesson Starter Chapter 3
Section 3 Counting Atoms
Chapter 3
Lesson Starter
Imagine that your semester grade depends 60% on exam scores and 40% on laboratory explorations.
Your exam scores would count more heavily toward your final grade.
In this section, you will learn that the atomic mass of an element is a weighted average of the masses of the naturally occurring isotopes of that element.

36. Section 3 Counting Atoms
Chapter 3
Objectives
Explain what isotopes are.
Define atomic number and mass number, and describe how they apply to isotopes.
Given the identity of a nuclide, determine its number of protons, neutrons, and electrons.
Define mole, Avogadro’s number, and molar mass, and state how all three are related.
Solve problems involving mass in grams, amount in moles, and number of atoms of an element.

37. Section 3 Counting Atoms
Chapter 3
Atomic Number
Atoms of different elements have different numbers of protons.
Atoms of the same element all have the same number of protons.
The atomic number (Z) of an element is the number of protons of each atom of that element.

38. Visual Concepts
Chapter 3
Atomic Number

39. Section 3 Counting Atoms
Chapter 3
Isotopes
Isotopes are atoms of the same element that have different masses.
The isotopes of a particular element all have the same number of protons and electrons but different numbers of neutrons.
Most of the elements consist of mixtures of isotopes.

40. Section 3 Counting Atoms
Chapter 3
Mass Number
The mass number is the total number of protons and neutrons that make up the nucleus of an isotope.

41. Visual Concepts
Chapter 3
Mass Number

42. Designating Isotopes Chapter 3
Section 3 Counting Atoms
Chapter 3
Designating Isotopes
Hyphen notation: The mass number is written with a hyphen after the name of the element.
uranium-235
Nuclear symbol: The superscript indicates the mass number and the subscript indicates the atomic number.

43. Section 3 Counting Atoms
Chapter 3
The number of neutrons is found by subtracting the atomic number from the mass number.
mass number  atomic number = number of neutrons
235 (protons + neutrons)  92 protons = 143 neutrons
Nuclide is a general term for a specific isotope of an element.

44. Visual Concepts
Chapter 3
Isotopes and Nuclides

45. Chapter 3 Sample Problem A
Section 3 Counting Atoms
Chapter 3
Sample Problem A
How many protons, electrons, and neutrons are there in an atom of chlorine-37?

46. Chapter 3 Sample Problem A Solution
Section 3 Counting Atoms
Chapter 3
Sample Problem A Solution
Given: name and mass number of chlorine-37
Unknown: numbers of protons, electrons, and neutrons
Solution:
atomic number = number of protons = number of electrons
mass number = number of neutrons + number of protons

47. Chapter 3 Sample Problem A Solution, continued
Section 3 Counting Atoms
Chapter 3
Sample Problem A Solution, continued
mass number of chlorine-37  atomic number of chlorine = number of neutrons in chlorine-37
mass number  atomic number = 37 (protons plus neutrons)  17 protons = 20 neutrons
An atom of chlorine-37 is made up of 17 electrons, 17 protons, and 20 neutrons.

48. Relative Atomic Masses
Section 3 Counting Atoms
Chapter 3
Relative Atomic Masses
The standard used by scientists to compare units of atomic mass is the carbon-12 atom, which has been arbitrarily assigned a mass of exactly 12 atomic mass units, or 12 amu.
One atomic mass unit, or 1 amu, is exactly 1/12 the mass of a carbon-12 atom.
The atomic mass of any atom is determined by comparing it with the mass of the carbon-12 atom.

49. Average Atomic Masses of Elements
Section 3 Counting Atoms
Average Atomic Masses of Elements
Average atomic mass is the weighted average of the atomic masses of the naturally occurring isotopes of an element.
Calculating Average Atomic Mass
The average atomic mass of an element depends on both the mass and the relative abundance of each of the element’s isotopes.

50. Chapter 3 Calculating Average Atomic Mass, continued
Section 3 Counting Atoms
Chapter 3
Calculating Average Atomic Mass, continued
Copper consists of 69.15% copper-63, which has an atomic mass of amu, and 30.85% copper-65, which has an atomic mass of amu.
The average atomic mass of copper can be calculated by multiplying the atomic mass of each isotope by its relative abundance (expressed in decimal form) and adding the results.

51. Chapter 3 Calculating Average Atomic Mass, continued
Section 3 Counting Atoms
Chapter 3
Calculating Average Atomic Mass, continued
(  amu) + (  amu) = amu
The calculated average atomic mass of naturally occurring copper is amu.

52. Relating Mass to Numbers of Atoms
Section 3 Counting Atoms
Chapter 3
Relating Mass to Numbers of Atoms
The Mole
The mole is the SI unit for amount of substance.
A mole (abbreviated mol) is the amount of a substance that contains as many particles as there are atoms in exactly 12 g of carbon-12.
Avogadro’s Number
Avogadro’s number—  1023—is the number of particles in exactly one mole of a pure substance.

53. Section 3 Counting Atoms
Chapter 3
Molar Mass
The mass of one mole of a pure substance is called the molar mass of that substance.
Molar mass is usually written in units of g/mol.
The molar mass of an element is numerically equal to the atomic mass of the element in atomic mass units.

54. Chapter 3 Gram/Mole Conversions
Section 3 Counting Atoms
Chapter 3
Gram/Mole Conversions
Chemists use molar mass as a conversion factor in chemical calculations.
For example, the molar mass of helium is 4.00 g He/mol He.
To find how many grams of helium there are in two moles of helium, multiply by the molar mass.

55. Chapter 3 Conversions with Avogadro’s Number
Section 3 Counting Atoms
Chapter 3
Conversions with Avogadro’s Number
Avogadro’s number can be used to find the number of atoms of an element from the amount in moles or to find the amount of an element in moles from the number of atoms.
In these calculations, Avogadro’s number is expressed in units of atoms per mole.

56. Section 3 Counting Atoms
Chapter 3
Solving Mole Problems

57. Determining the Mass from the Amount in Moles
Section 3 Counting Atoms
Chapter 3
Determining the Mass from the Amount in Moles

58. Chapter 3 Sample Problem B
Section 3 Counting Atoms
Chapter 3
Sample Problem B
What is the mass in grams of 3.50 mol of the element copper, Cu?

59. Chapter 3 Sample Problem B Solution Given: 3.50 mol Cu
Section 3 Counting Atoms
Chapter 3
Sample Problem B Solution
Given: 3.50 mol Cu
Unknown: mass of Cu in grams
Solution: the mass of an element in grams can be calculated by multiplying the amount of the element in moles by the element’s molar mass.

60. Chapter 3 Sample Problem B Solution, continued
Section 3 Counting Atoms
Chapter 3
Sample Problem B Solution, continued
The molar mass of copper from the periodic table is rounded to g/mol.

61. Chapter 3 Sample Problem C
Section 3 Counting Atoms
Chapter 3
Sample Problem C
A chemist produced 11.9 g of aluminum, Al. How many moles of aluminum were produced?

62. Section 3 Counting Atoms
Chapter 3
Sample Problem C Solution
Given: 11.9 g Al
Unknown: amount of Al in moles
Solution:
The molar mass of aluminum from the periodic table is rounded to g/mol.

63. Chapter 3 Sample Problem D
Section 3 Counting Atoms
Chapter 3
Sample Problem D
How many moles of silver, Ag, are in 3.01  1023 atoms of silver?

64. Chapter 3 Sample Problem D Solution Given: 3.01  1023 atoms of Ag
Section 3 Counting Atoms
Chapter 3
Sample Problem D Solution
Given: 3.01  1023 atoms of Ag
Unknown: amount of Ag in moles
Solution:

65. Chapter 3 Sample Problem E
Section 3 Counting Atoms
Chapter 3
Sample Problem E
What is the mass in grams of 1.20  108 atoms of copper, Cu?

66. Chapter 3 Relating Mass to Numbers of Atoms, continued
Section 3 Counting Atoms
Chapter 3
Relating Mass to Numbers of Atoms, continued
Sample Problem E Solution
Given: 1.20  108 atoms of Cu
Unknown: mass of Cu in grams
Solution:
The molar mass of copper from the periodic table is rounded to g/mol.

67. End of Chapter 3 Show

68. Multiple Choice Chapter 3
Standardized Test Preparation
Chapter 3
Multiple Choice
1. A chemical compound always has the same elements in the same proportions by mass regardless of the source of the compound. This is a statement of
A. the law of multiple proportions.
B. the law of isotopes.
C. the law of definite proportions.
D. the law of conservation of mass.

69. Multiple Choice Chapter 3
Standardized Test Preparation
Chapter 3
Multiple Choice
2. An important result of Rutherford’s experiments with gold foil was to establish that
A. atoms have mass.
B. electrons have a negative charge.
C. neutrons are uncharged particles.
D. the atom is mostly empty space.

70. Multiple Choice Chapter 3
Standardized Test Preparation
Chapter 3
Multiple Choice
3. Which subatomic particle has a charge of +1?
A. electron
B. neutron
C. proton
D. meson

71. Multiple Choice Chapter 3 4. Which particle has the least mass?
Standardized Test Preparation
Chapter 3
Multiple Choice
4. Which particle has the least mass?
A. electron
B. neutron
C. proton
D. All have the same mass.

72. Multiple Choice Chapter 3 5. Cathode rays are composed of
Standardized Test Preparation
Chapter 3
Multiple Choice
5. Cathode rays are composed of
A. alpha particles.
B. electrons.
C. protons.
D. neutrons.

73. Multiple Choice Chapter 3
Standardized Test Preparation
Chapter 3
Multiple Choice
6. The atomic number of an element is the same as the number of
A. protons.
B. neutrons.
C. protons + electrons.
D. protons + neutrons.

74. Multiple Choice Chapter 3
Standardized Test Preparation
Chapter 3
Multiple Choice
7. How many neutrons are present in an atom of tin that has an atomic number of 50 and a mass number of 119?
A. 50
B. 69
C. 119
D. 169

75. Multiple Choice Chapter 3
Standardized Test Preparation
Chapter 3
Multiple Choice
8. What is the mass of 1.50 mol of sodium, Na?
A g
B g
C g
D g

76. Multiple Choice Chapter 3
Standardized Test Preparation
Chapter 3
Multiple Choice
9. How many moles of carbon are in a 28.0 g sample?
A. 336 mol
B mol
C mol
D mol

77. Standardized Test Preparation
Chapter 3
Short Answer
10. Which atom has more neutrons, potassium-40 or argon-40?

78. Standardized Test Preparation
Chapter 3
Short Answer
11. What is the mass of 1.20  1023 atoms of phosphorus?

79. Extended Response Chapter 3
Standardized Test Preparation
Chapter 3
Extended Response
12. Cathode rays emitted by a piece of silver and a piece of copper illustrate identical properties. What is the significance of this observation?

80. Extended Response Chapter 3
Standardized Test Preparation
Chapter 3
Extended Response
13. A student believed that she had discovered a new element and named it mythium. Analysis found it contained two isotopes. The composition of the isotopes was 19.9% of atomic mass and 80.1% of atomic mass What is the average atomic mass, and do you think mythium was a new element?

81. Important facts

82. Unit 1 • Investigation III82

83. Here is a Bohr model of a carbon atom.
Unit 1 • Investigation III 83

84. Beryllium Atom
Fluorine Atom
Carbon Atom
Unit 1 • Investigation III 84

85. All matter is made up of extremely small particles called atoms
All matter is made up of extremely small particles called atoms. These particles are too small to be seen even with a microscope.
Science is theoretical and dynamic. Models and theories are continually being revised, refined, or replaced with new models and theories.
Unit 1 • Investigation III 85

86. Atomic number is the number of protons in the nucleus of an atom.
Mass number is the mass of an individual atom.
Unit 1 • Investigation III 86

87. element chemical symbol atomic number # of protons # of electrons
# of neutrons
mass number
atomic weight
beryllium Be 4 5 9
9.001
fluorine F 10 19
18.9
Carbon C 6 12
12.011
chlorine Cl 17 18 35
35.45
lead
126
potassium 39
tin 70
tungsten
184
183.85 29 36
gold
118
Unit 1 • Investigation III 87

88. If you know the atomic number of an element, what other information can you figure out about the atoms of that element?
If you know the atomic number of an element, can you figure out how many neutrons an atom of that element has?.
Unit 1 • Investigation III 88

89. Mass number is the number of protons plus the number of neutrons.
Atomic mass is the “weight” or mass of a single atom.
Atomic weight is the decimal number on the periodic table.
Unit 1 • Investigation III 89

90. Practice Use your periodic table to identify the following elements:
a) Atomic number 10
b) Has five electrons
c) Atomic mass of 15.99
Unit 1 • Investigation III 90

91. The atomic number is equal to the number of protons.
Each successive element has one more proton than the element preceding it.
The atomic number is equal to the number of protons.
Unit 1 • Investigation III 91

92. The number of electrons is equal to the number of protons (as long as the atom is neutral).
The mass number is equal to the number of protons plus the number of neutrons (most of the mass is found in the nucleus).
Unit 1 • Investigation III 92