1. Atoms and Their Structure

2. Objective Explain Thompsons Cathode ray experiments and atomic model
Explain Milikan’s Oil
Name important atomic scientists

4. History of the Atom Democritus
All matter is composed of very small, indivisible particles called a-tomos. 400BC

5. Who’s Next?
John Dalton ( ), an English school teacher and chemist, studied the results of experiments by other scientists.

6. Dalton’s Atomic Theory
John Dalton atomic theory of matter
With only a few changes over the years, Dalton’s theory has remained essentially intact up to the present time.

7. Dalton’s Atomic Theory
All matter is made of tiny indivisible particles called atoms.
Atoms of the same element are identical; those of different atoms are different.

8. Dalton’s Atomic Theory, cont.
Atoms of different elements combine in whole number ratios to form compounds.
Chemical reactions involve the rearrangement of atoms. No new atoms are created or destroyed.

9. Parts of the Atom
Dalton’s atomic theory, most scientists in the 1800s believed that the atom was like a tiny solid ball that could not be broken up into parts.
In 1897, a British physicist, J.J. Thomson, discovered that this solid-ball model was not accurate.

10. Parts of the Atom Thomson’s experiments used a cathode ray tube.
It is a vacuum tube - all the air has been pumped out.

11. Where did Cathode Ray Tubes (CRT) come from?
Started with Geissler tubes

14. Crooke’s Tubes
Extremely Low Pressure

16. Crookes Tubes

18. Enter J.J. Thomson
In 1897 he showed that cathode rays consist of particles - electrons - that conduct electricity. Thomson also concluded that electrons are part of atoms.
He discovered electrons and managed to estimate it’s magnitude (amount) by performing experiments with charged particles in gases.

19. So What’s Going On Here???
Problem 1: We know the CRT ray is negative but can the charge be separated from the ray?
Problem 2: Is the CRT ray a wave or particle?

20. Voltage source - +
Vacuum tube
Metal Disks

21. Voltage source - +
At each end of the tube is a metal piece called an electrode, which is connected through the glass to a metal terminal outside the tube.

22. Voltage source - +
When the electrodes are charged, rays travel in the tube from the negative electrode, which is the cathode, to the positive electrode, the anode.

23. Voltage source - +
Because these rays originate at the cathode, they are called cathode rays.

24. Voltage source - +

25. Voltage source - +

26. Voltage source + -
By adding an electric field,

27. Voltage source + -
The rays bent toward a positively charged plate and away from a negatively charged plate.

28. Voltage source + -
Objects with like charges repel each other, and objects with unlike charges attract each other.

29. Voltage source + -
By adding an electric field it was found that the moving rays were negative.

31. Thomson’s Model Dalton’s model
From Thomson’s experiments, atoms were composed of electrically charged particles.

32. Thomson’s Model
Sketch Thomson’s model of the atom in your notes.

33. Thomson’s Model
Matter is not negatively charged, so atoms can’t be negatively charged either.
If atoms contained extremely light, negatively charged particles, then they must also contain positively charged particles — probably with a much greater mass than electrons.

34. Thomson’s Model
J.J. Thomson said the atom was like plum pudding, a popular English dessert.

35. Millikan’s Oil Drop Experiment
R.A. Millikan found the charge of an electron to be x Coulombs in his famous oil drop experiment.

36. The Proton
In 1886, scientists discovered that a cathode-ray tube emitted rays not only from the cathode but also from the positively charged anode.
Years later, scientists determined that the rays were composed of positively charged subatomic particles called protons.

37. The Proton
At this point, it seemed that atoms were made up of equal numbers of electrons and protons.

38. Ernest Rutherford
In 1909, a team of scientists led by Ernest Rutherford in England carried out the first of several important experiments that revealed an arrangement far different from the plum pudding model of the atom and discovered the nucleus.

39. Rutherford’s Experiment
The experimenters set up a lead-shielded box containing radioactive polonium, which emitted a beam of positively charged subatomic particles through a small hole.

40. Florescent
Screen
Lead block
Polonium
Gold Foil

41. What Rutherford Expected
The alpha particles to pass through without changing direction very much.

42. Because he thought the mass was evenly distributed in the atom,

43. the alpha particles should go straight through.

44. What Rutherford Observed

45. How Rutherford Explained It
To explain the results of the experiment, Rutherford’s team proposed a new model of the atom.
Because most of the particles passed through the foil, they concluded that the atom is nearly all empty space.

46. How Rutherford Explained It
Alpha particles are deflected by the nucleus if they get close enough it.

47. How Rutherford Explained It
Because so few particles were deflected, they proposed that the atom has a small, dense, positively charged central core, called a nucleus.
Most of the atom’s mass is located in the nucleus. 47

48. The Nuclear Model of the Atom
Sketch Rutherford’s model of the atom in your notes.

49. Isotopes
In 1910, J.J. Thomson discovered that neon consisted of atoms of two different masses.

50. C Isotopes Carbon-12 and carbon-14 are isotopes of one another.6 C 14
Carbon-12 and carbon-14 are isotopes of one another.
They are the same element with different masses.

51. Isotopes
Atoms of an element that are chemically alike but differ in mass are called isotopes of the element.
Because of the discovery of isotopes, scientists hypothesized that atoms contained still a third type of particle that explained these differences in mass.

52. The Neutron
Isotopes of an element differ in the number of the subatomic particle called neutrons.

53. The Neutron
Calculations showed that the neutron should have a mass equal to that of a proton but no electrical charge.
The existence of this neutral particle, called a neutron, was confirmed in the early 1930s.
James Chadwick is given credit for discovering the neutron.

54. Subatomic Particles Name Electron e- -1 1/2000 Proton p+ +1 1 Neutron
Relative
mass
Relative
mass
Name
Symbol
Symbol
Charge
Charge
Electron e- -1
1/2000
Proton p+ +1 1
Neutron n0 1

55. ALMOST EVERYTHING we do in this class will only deal with these 3 particles PROTON ELECTRON NEUTRON

57. Masses
The mass of a neutron is almost the same as the mass of a proton.
The sum of the protons and neutrons in the nucleus is the mass number of that particular atom.
The mass number (A) is the atomic mass rounded to a whole number.

58. Modern View of the Atom The atom has two regions and is 3-dimensional.
The nucleus is at the center and contains the protons and neutrons.

60. AMU Atomic mass unit

62. Modern View of the Atom
The electron cloud is the region where you might find an electron and most of the volume of an atom.

63. Draw this diagram in your notes.
Model of Atoms
Draw this diagram in your notes.

64. Atomic Number
The atomic number (Z) of an element is the number of protons in the nucleus of an atom of that element.
The number of protons determines identity of an element, as well as many of its chemical and physical properties.

65. Atomic Number
Because atoms have no overall electrical charge, an atom must have as many electrons as there are protons in its nucleus.
Therefore, the atomic number of an element also tells the number of electrons in a neutral atom of that element.

66. SYMBOLS
Draw the following in your notes. 66

67. 108 Ag 47
The smaller number is the atomic number. The atomic number equals the number of protons and the number of electrons in neutral atoms.

68. 108 Ag 47
The larger number is the mass number. The mass number equals the number of protons PLUS the number of neutrons mass # - atomic # = # neutrons

69. Ag 108 47 Silver-108 has ____ protons,
____ electrons, and _____ neutrons. 47 47 61

70. Model of a Hydrogen Atom
Hydrogen has _____ proton, _____ electron, and _____ neutrons.
one
one
zero

71. Naming Isotopes C-12 C-14 Pb-210 Pb-212
Put the mass number after the symbol of the element.
Carbon – amu
C-12
Carbon – amu
C-14
Pb-210
Lead – amu
Pb-212
Lead – amu

72. Model of a Helium Atom
Helium has _____ protons, _____ electrons, and _____ neutrons.
two
two
two

73. Model of a Boron Atom
5 p+
6 no
Boron has _____ protons, _____ electrons and _____ neutrons.
five
five
six

74. Model of a Carbon Atom
Carbon has _____ protons, _____ electrons and _____ neutrons.
six
six
six

75. Isotopes
Remember, isotopes of an element have different mass numbers because they have different numbers of neutrons, but they all have the same atomic number.

76. Isotopes
Subtract the atomic number from the mass number to determine the number of neutrons.
How many neutrons are in each lithium isotope below?
4 neutrons
3 neutrons
5 neutrons 76

77. Information in the Periodic Table
The average atomic mass is the weighted average mass of all the naturally occurring isotopes of that element.

78. Average Atomic Mass
The average atomic mass of the element is the sum of the mass contributions of each isotope.

79. SYMBOLS 79

80. Write the complete symbol for sodium.23 Na 11
To write the complete symbol for an element, the atomic number will go in the lower left corner of the element symbol.

81. Write the complete symbol for magnesium-26.Mg 12
To write the complete symbol for an element, the atomic number will go in the lower left corner of the element symbol.

82. Symbols Example F 19 9
Determine the complete symbol for a fluorine atom with a mass number of 19.

83. Symbols Example
1) Determine the following for the fluorine atom depicted below. 19 F
(9)
number of protons 9
number of neutrons
(10)
number of electrons
(9)
atomic number
(9)
e) mass number
(19) 83

84. Symbols Example Br 80 35
Determine the complete symbol for a bromine atom with a mass number of 80. 84

85. Symbols Problem
2) Determine the following for the bromine atom depicted below. 80 Br
(35)
number of protons 35
number of neutrons
(45)
number of electrons
(35)
atomic number
(35)
e) mass number
(80)

86. Symbols Problem
3) If an element has an atomic number of 34 and a mass number of 78 what is the
(34)
number of protons
number of neutrons
(44)
number of electrons
(34)
complete symbol 78 Se 34

87. Symbols Problem
4) If an element has 91 protons and 140 neutrons what is the
(91)
atomic number
mass number
(231)
number of electrons
(91)
complete symbol
231 Pa 91

88. Symbols Problem
5) If an element has 78 electrons and 117 neutrons what is the
(78)
atomic number
mass number
(195)
number of protons
(78)
complete symbol
195 Pt 78

89. EXIT TICKET PLEASE GET OUT A SHEET OF PAPER. PUT YOUR NAME AT THE TOP.
ON THE FIRST LINE WRITE
EXIT TICKET – SUBATOMIC PARTICLES
AND TODAY’S DATE

90. 1) Fill in the chart below.
Element
# of Protons
# of Neutrons
# of Electrons
Mass #
Atomic #
Potas-sium
Argon 19 20 19 39 19 18 22 18 40 18

91. 2). Fill in the chart below
2) Fill in the chart below. (When numbers are provided, the isotope represented by each space may NOT be the most common isotope or the one closest in atomic mass to the value on the periodic table.)
Element
# of Protons
# of Neutrons
# of Electrons
Mass #
Atomic #
Chlorine
Oxygen 17 20 17 37 17 8 10 8 18 8

92. End of Day 1