1. Atom Unit

2. Standard
7.PS Develop and use Models to illustrate the structure of Atoms, including the Subatomic Particles with their Relative Positions and Charges.

4. Element
Substance that CANNOT be broken down into simpler Substances. It is a Matter made of Atoms of only one kind
Example—Iron is only made of iron atoms
118 Elements on Periodic Table

5. Atom Smallest part of an Element
Consist of a Nucleus surrounded by one or more Electrons

8. I. Scientists who contributed to the knowledge of the Atom
The Theory of the Atom has changed over time

9. Timeline BCE means Before Common Era AD means Anno Domini
(Year of Our Lord)

10. A. Democritus
Born 460 BCE
Died 370 BCE

11. Democritus
A Greek Philosopher, who theorized that if you cut an object in half repeatedly, you would end up with a particle that could not be cut. (ATOM)
Atom (Greek word: ATOMAS) meaning “not able to be divided”

12. B. Aristotle
Born 384 BCE
Died 322 BCE

13. Aristotle
Greek Philosopher, who believed that you would never end up with a particle that could not be cut
More Influential
He was WRONG

14. C. John Dalton
Born AD 1766
Died AD 1844

15. John Dalton British School Teacher / Chemist
Combined his idea of Element with
Greek Theory of the Atom
He proposed the following ideas
about Matter:

16. Matter is made up of Atoms.
Atoms cannot be divided into smaller pieces.
All the Atoms of an Element are exactly alike.
Different Elements are made of different kinds of Atoms.

17. D. William Crooke
Born AD 1832
Died AD 1919

18. William Crooke Start of Scientific Evidence
(No Lab Experiments before this
time)
Glass tube that had almost all the air removed from it.
The glass tube had two pieces of metal called Electrodes.

20. Electrode is a piece of Metal that can Conduct Electricity.
Anode an Electrode that has a Positive End.
Cathode an Electrode that has a Negative End.

29. Crooke hypothesized that the green glow in the tube was caused by Rays, or Streams of particles.
Rays were called Cathode Rays
Used in TV and Computer Screens

30. E. J.J. Thomson
Born AD 1856
Died AD 1940

31. J. J. Thomson Tested Crooke’s Experiment
Was the Greenish Glow Light, or was it a stream of charged particles?
Placed a Magnet beside the tube
from Crooke’s experiment.

32. The Beam is bent in the direction of the Magnet.
Light cannot be bent by a Magnet, as the beam couldn’t be Light.
Conclusion—must be a charged particle that came from the Cathode.

33. He showed that there was a mistake with Dalton’s Theory
He showed that there was a mistake with Dalton’s Theory. The Atom could be divided into smaller pieces.
Electrons  Negatively charged particle that exists in an Electron Clouds formation around an Atom’s Nucleus

34. F. Ernest Rutherford
Born AD 1871
Died AD 1937

35. Ernest Rutherford Former student of Thomson’s
Designed an experiment to study the
parts of the Atom
He aimed a beam of small, positively
particles at a thin sheet of Gold Foil
He placed a coated screen around the
foil
The coating glowed when hit by the
positively charged particles

38. Hypothesized that almost all the Mass of the Atom and all of its Positive charge are crammed in the center of the Atom called the Nucleus.
Proton Positive charge particle present in the Nucleus of all Atoms.

39. An Atom’s Electron have almost No Mass.
Neutron Neutral particle that has the same Mass as a Proton and is found in an Atom’s Nucleus

40. G Niels Bohr
Born AD 1885
Died AD 1962

41. Niels Bohr Danish scientist who worked with Rutherford
Studied the way Atoms react
with Light
Electrons travel in a region
surrounding the nucleus called
the Electron Cloud.

42. II. Parts of the Atom Size of an Atom: Dot on your paper
2 Million Atoms
Penny –
20,000,000,000,000,000,000,000
Atoms or 2 X 10²² Atoms of Copper and Zinc

43. A. Nucleus (Center Atom)
Proton  Positively Charged Particle
--All Protons are Identical
Neutron  No Electrical Charged Particle
--All Neutrons are Identical

44. Nucleus (Center Atom) Neutrons are slightly Larger than Protons
Majority of Mass in Atom
(Protons/Neutrons)

45. B. Outside the Nucleus Electron  Negatively Charged Particle
Has hardly any Mass
Very Small (1,800 Electrons equal
Mass of 1 Proton)

46. Outside the Nucleus
Electrons are found around the Nucleus in what is called Electron Clouds

47. Mass Proton = Mass Neutron
Mass Proton > Mass Electron
Mass Neutron > Mass Electron

48. III. How do Atoms in an Element Differ?
Elements differ by their number of Protons, Neutrons, and Electrons in each Atom.
 The different numbers of each will give the Atom Special Properties

49. How do Atoms in an Element Differ?
Elements can differ in charge
The Element will either have a Neutral Charge (Proton = Electron),
Positive Charge (Protons > Electrons), or Negative Charge (Electrons >
Protons)

50. Ion
Atom that is No longer Neutral because it has gained or lost an Electron

52. Problem 1
Protons 50 _________
Find the Amount of Electrons in the following Charges
+1 =
+12 =
-15 =
-100 =

53. Protons 50 Mercury
Find the Amount of Electrons in the following Charges
+1 =
+12 =
-15 =
-100 =

54. Protons 50 Mercury
Find the Amount of Electrons in the following Charges
+1 = 79 e-
+12 =
-15 =
-100 =

55. Protons 50 Mercury
Find the Amount of Electrons in the following Charges
+1 = 79 e-
+12 = 68 e-
-15 =
-100 =

56. Protons 50 Mercury
Find the Amount of Electrons in the following Charges
+1 = 79 e-
+12 = 68 e-
-15 = 95 e-
-100 =

57. Protons 50 Mercury
Find the Amount of Electrons in the following Charges
+1 = 79 e-
+12 = 68 e-
-15 = 95 e-
-100 = 180 e-

58. Problem 2
Protons 45 _________
Find the Amount of Electrons in the following Charges
+5 =
+15 =
-30 =
-60 =

59. Protons Rhodium
Find the Amount of Electrons in the following Charges
+5 =
+15 =
-30 =
-60 =

60. Protons Rhodium
Find the Amount of Electrons in the following Charges
+5 = 40 e-
+15 =
-30 =
-60 =

61. Protons Rhodium
Find the Amount of Electrons in the following Charges
+5 = 40 e-
+15 = 30 e-
-30 =
-60 =

62. Protons Rhodium
Find the Amount of Electrons in the following Charges
+5 = 40 e-
+15 = 30 e-
-30 = 75 e-
-60 =

63. Protons Rhodium
Find the Amount of Electrons in the following Charges
+5 = 40 e-
+15 = 30 e-
-30 = 75 e-
-60 = 105 e-

64. IV. Atomic Structure of an Atom
All Atoms are made up of 3 Subatomic Particles
Proton
Neutron
Electron
*** Most of an Atom is Empty Space

65. You must know 3 things about each Subatomic Particle
What is the Charge?
Where can it be Found?
What is its JOB?

66. A. Proton Positive Charge Found in Nucleus of an Atom
Identification of Element

69. B. Neutron Neutral Charge Found in Nucleus of Atom
Radioactive (Yes or No)
Yes if Neutrons > Protons
No if Protons > Neutrons

70. C. Electron Negative Charge
Found Outside the Nucleus in a region called the Electron Cloud
Binding or Glue to form Compounds

71. D. Atomic Number
Is the number of Protons in the Nucleus of an Atom of that Element.
The Atoms of different Elements contain different numbers of Protons.

72. Examples Hydrogen has 1 Proton, Carbon has 6 Protons, Oxygen has 8 Protons, Iodine has 53 Protons, Mercury has 80 Protons, and Plutonium has 94 Protons
Atoms of an Element are identified by the number of Protons because this number never changes without changing the identity of the Element.

73. Mass Number The sum of Neutrons and Protons in the Nucleus of an Atom.
To calculate the number of Neutrons in an Isotope you must subtract the Atomic Number from the Mass Number of the Isotope.

74. 2 He
4.00
Protons =
Electrons =
Neutrons =

75. 2 He
4.00
Protons = 2
Electrons =
Neutrons =

76. 2 He
4.00
Protons = 2
Electrons = 2
Neutrons =

77. 2 He
4.00
Protons = 2
Electrons = 2
Neutrons = 2

78. 6 C
12.00
Protons =
Electrons =
Neutrons =

79. 6 C
12.00
Protons = 6
Electrons =
Neutrons =

80. 6 C
12.00
Protons = 6
Electrons = 6
Neutrons =

81. 6 C
12.00
Protons = 6
Electrons = 6
Neutrons = 6

82. 82 Pb
207.2
Protons =
Electrons =
Neutrons =

83. 82 Pb
207.2
Protons = 82
Electrons =
Neutrons =

84. 82 Pb
207.2
Protons = 82
Electrons = 82
Neutrons =

85. 82 Pb
207.2
Protons = 82
Electrons = 82
Neutrons = 125

86. 80 Hg
200.6
Protons =
Electrons =
Neutrons =

87. 80 Hg
200.6
Protons = 80
Electrons =
Neutrons =

88. 80 Hg
200.6
Protons = 80
Electrons = 80
Neutrons =

89. 80 Hg
200.6
Protons = 80
Electrons = 80
Neutrons = 120

90. 1 H
Protons =
Electrons =
Neutrons =

91. 1 H
Protons = 1
Electrons =
Neutrons =

92. 1 H
Protons = 1
Electrons = 1
Neutrons =

93. 1 H
Protons = 1
Electrons = 1
Neutrons = 0

94. 92 U
238.0
Protons =
Electrons =
Neutrons =

95. 92 U
238.0
Protons = 92
Electrons =
Neutrons =

96. 92 U
238.0
Protons = 92
Electrons = 92
Neutrons =

97. 92 U
238.0
Protons = 92
Electrons = 92
Neutrons = 146

98. E Neutrons
The Atomic Number is the number of Protons, but what about the number of Neutrons in an Atom’s Nucleus.
A particular type of Atom can have a varying number of Neutrons in its Nucleus

99. Isotopes
Are Atoms of the same Element that have different numbers of Neutrons.
Carbon-12 (Normal)
Carbon-13 (Isotope)
Carbon-14 (Isotope)

101. Helium Isotopes

102. Radioactive Decay
Many Atomic Nuclei are stable when they have about the same number of Protons and Neutrons.
Some become unstable when too many or too few Neutrons.

103. Examples Uranium and Plutonium
Repulsion builds up because the Nucleus must release a particle to become Stable
When particles are Released, Energy is Given Off

104. Radioactive Decay release of Nuclear particles and Energy from Unstable Nuclei
Transmutation the changing of one Element into another through Radioactive Decay
Example – Smoke Alarm

105. Transmutation (Fire Alarm)
Americium --- Neptunium (Am) (Np) 95 Protons 93 Protons 146 Neutrons 144 Neutrons -- Makes Electric Current

107. Half-Life
Half-Life time needed for one-half of the mass of a sample of a radioactive isotope to decay.

109. Half –Life Problem:
Tritium has a Half-Life of 12.5 years. If you start with 20 grams of Tritium, how much is left after 50 years?

110. Half –Life Problem:
Cycles = __50 Years__
12.5 Years
Cycles = 4 Cycles

111. Half –Life Problem:
Grams = 10 g 2
Grams = 5g

112. Half –Life Problem:
Grams = 2.5 g 2
Grams = 1.25 g

113. Carbon Dating Carbon-14 Half-Life of 5,730 Years.
Radioactive Decay is useful in determining the Age of Artifacts and Fossils.
Carbon-14 Half-Life of 5,730 Years.

114. Carbon Dating
In a living Organism, the amount of Carbon-14 remains in Constant Balance with the levels of the Isotope in the Atmosphere or Ocean.
The Balance occurs because Living Organisms take in and release Carbon.

115. Carbon Dating
While life processes go on, any Carbon-14 Nucleus that Decays is replaced by another from the Environment.
When the Plant and Animal dies, the Decaying Nuclei no longer can be replaced.

116. V. Calculating the Mass of an Element
Atomic Mass  of an Element is the weighted average of the Masses of all the naturally occurring Isotopes of that Element
Atomic Mass Unit = AMU

117. Atomic Mass Problem
Chlorine-35 makes up 76% of all the Chlorine in nature, and Chlorine-37 makes up the other 24%. What is the Atomic Mass of Chlorine?

118. Atomic Mass Problem Cl – 35 x .76 = 26.60 Cl – 37 x .24 = 8.80
= amu

119. VI. Forces of an Atom
Gravitational Force – depends on Mass and Distance Apart
-- since Atom very small this Force is Small

120. Forces of an Atom
2. Electromagnetic Force – objects that have the same Charge Repel each other, while objects with Opposite charge Attract each other -- Strong Force

121. Forces of an Atom Strong Force -- Protons push away from each other
-- Strongest Force

122. Forces of an Atom
4. Weak Force – Occurs in Radioactive Atoms when Neutrons change to Protons -- Weak Force