1. Atomic Structure What does the atom look like???

2. Early Models of the Atom
Democritus: c BC Greek Philosopher
matter is composed of tiny, discrete, indivisible particles called atomos (Greek word meaning indivisible).
Ideas based on philosophical speculation
Theory not accepted due to influence of Aristotle
An atom is the smallest part of
an element that retains the
chemical properties of that
element. It cannot be broken down
by ordinary means.

3. Antoine Laurent Lavoisier: A.D. 1780
Law of Conservation of Matter states that matter is neither created nor destroyed, it only changes form.
1st to announce that air was made up of 2 gases – oxygen and azote (nitrogen)
Work done on combustion, oxidation, and gases
Lavoisier is known as the Father of Chemistry.

4. In 1771, at age 28, Lavoisier married the 13-year-old Marie-Anne Pierrette Paulze.
Over time, she proved to be a scientific colleague to her husband.
She translated documents and chemistry books from English.
She created many sketches and carved engravings of the laboratory instruments he used.
She also edited and published Lavoisier’s memoirs after his death.
She hosted parties at which eminent scientists discussed ideas and problems related to chemistry.

5. Lavoisier was Guillotined May 8, 1794
An appeal to spare his life so that he could continue his experiments was cut short by a judge saying: "The Republic needs neither scientists nor chemists; the course of justice cannot be delayed.”
One and a half years following his death, Lavoisier was exonerated by the French government.
When his private belongings were delivered to his widow, a brief note was included reading "To the widow of Lavoisier, who was falsely convicted."

6. Joseph Louis Proust: A.D. 1799
Law of Definite Proportion states that compounds always have the same elements in the same
proportion by mass.
Ex) the ratio of H:O
in water is always 2:16.

7. John Dalton A.D.1766-1844 English schoolteacher Some of the original
chemical symbols
from his book:

8. John Dalton: A.D. 1803-1808 Proposed Atomic Theory of Matter:
An element is composed of extremely small, indivisible particles called atoms
All atoms of a given element have identical properties that differ from those of other elements
Atoms cannot be created, destroyed, or transformed into atoms of other elements

9. Dalton’s Atomic Theory (cont.)
Compounds are formed when atoms of different elements combine with one another in small whole-number ratios
In chemical reactions, atoms are combined, separated, or rearranged
Dalton is credited as being the
Father of the Modern Atomic Theory

10. Law of Multiple Proportions proposed by Dalton
If 2 or more different compounds are composed of the same two elements, then the ratios of the masses of the 2nd element is always a ratio of small whole numbers
CO (1.0 g C/1.33 g O)
CO2 (1.0 g C/2.66g O)
2:1 ratio of O in the compounds
NO (1.0 g N/1.14 g O)
NO2 (1.0 g N/2.28 g O)

11. Benjamin Franklin: 1706-1790 American statesman/scientist
Ben’s lightning rod in the Franklin Institute

12. In 1752 Benjamin Franklin Experimented with electricity
He found that an object can have a positive or a negative charge.
negative and negative: repel
negative and positive: attract
positive and positive: repel

13. Michael Faraday (1839) English scientist
Hypothesized that atoms
contain electric charge.
Built 1st electrical motor
Introduced words such as…
Ion, electrode, anode and cathode
A unit of electricity was named after him = farad
Static Electricity = electrons move and then are at rest (grounded)

14. William Crookes – 1875 English scientist
Cathode Ray Tube: An evacuated glass tube with gas at low pressure
Electricity is passed through 2 electrodes: cathode (negative) and anode (positive)
Light is cast from cathode to anode (look at the shadow)
Magnet deflects light – this proved that particles have charge and mass.

15. Crookes’ Conclusion Light is composed of negatively charged particles
Discovered based upon magnet deflection and anode shadow
Crooke’s Maltese Cross
You Tube Demo
Video Clip Crooke’s Tube

16. J.J. Thompson: 1897
English Physicist who said a cathode ray is made of electrons, they
have mass (9.1 x 10-28g) and are negatively charged particles. Thus he
is credited with “discovering” electrons.

17. Cathode Ray Tube (McGraw Hill)
J.J. Thomson
Used Crookes tube (gas discharge tube)
Applied positive and negative field to a beam of cathode rays. The deflection was the same for all gases.
Experimentally proved the existence of the electron (e-)
Cathode Ray Tube (McGraw Hill)

18. Thomson Experimented with hydrogen gas at low pressure
2nd beam of particles was moving towards the cathode, therefore, positive particles
Deflection of positive ions varied with different gases
Hydrogen ions had the greatest deflection, therefore, the smallest positive mass
Hydrogen ion deflection was smaller than that of the electron, therefore more massive than an electron
Hydrogen ion = proton

19. J.J. Thomson
Calculated the charge to mass ratio, (e/m= x 108C/g), using different cathode metals and different gases
Measured how much they were deflected by a magnetic field and how much energy they carried.
He found that the charge to mass ratio was over a thousand times higher than that of a hydrogen ion, suggesting either that the particles were very light or very highly charged.
Credit:Science Museum/Science & Society Picture Library

20. J.J. Thomson Made a bold conclusion:
Cathode rays were indeed made of particles which he called “corpuscles," and these corpuscles came from within the atoms of the electrodes themselves, meaning the atoms were, in fact, divisible.
Won a Nobel Prize in Physics in 1906.

21. J.J. Thomson: 1897
Thought the atom was made up of these corpuscles (negative charges) distributed in a sea of positive charge
Related it to “plum pudding”
Different models of
the plum
pudding model

22. Robert Millikan:1909 American scientist
Oil drop experiment
Measured voltage to determine the charge on one electron
-1.60 x coulomb/e-
Used Thomson’s charge to mass ratio to calculated the mass of an electron
Mass of 1 electron
= x 10-28g

23. An atomizer sprayed a fine mist of oil droplets into the upper chamber
An atomizer sprayed a fine mist of oil droplets into the upper chamber. Some of these tiny droplets fell through a hole in the upper floor into the lower chamber of the apparatus.
Next, Millikan applied a charge to the falling drops by irradiating the bottom chamber with x-rays. This caused the air to become ionized, which means that the air particles lost electrons.
A part of the oil droplets captured one or more of those extra electrons and became negatively charged
By attaching a battery to the plates of the lower chamber he created an electric field between the plates that would act on the charged oil drops
He adjusted the voltage till the electric field force would just balance the force of gravity on a drop, and the drop would hang suspended in mid-air.
Some drops have captured more electrons than others, so they will require a higher electrical field to stop
Particles that did not capture any of that extra electrons were not affected by the electrical field and fell to the bottom plate due to gravity.
When a drop is suspended, its weight  m · g  is exactly equal to the electric force applied, the product of the electric field and the charge q · E.
The values of E (the applied electric field), m (the mass of a drop which was already calculated by Millikan), and g (the acceleration due to gravity), are all known values. Unknown charge on the drop, q
m · g = q · E
Millikan repeated the experiment numerous times varying the strength of the x-rays ionizing the air so that differing numbers of electrons would jump onto the oil molecules each time.
He obtained various values for q. The charge q on a drop was always a multiple of 1.59 x Coulombs.
This is less than 1% lower than the value accepted today: x C.

24. Ernest Rutherford: 1903 Rutherford studies under Thomson.
He discovered 3 types of natural radiation or radioactive decay.
α - Alpha Particles
β - Beta Particles
γ - Gamma Rays
high energy X-rays

25. Rutherford’s Gold Foil Experiment 1909
This experiment showed the atom has a small, central positive nucleus and that most of the atom is empty space.
Rutherford Video Clip

26. Rutherford’s Gold Foil Experiment
Used a narrow beam of  particles to bombard targets made of thin sheets of gold. Metal foil was surrounded by a fluorescent screen.
Results:
most of the  particles passed through the foil
some were deflected at small angles
few were deflected at large angles

27. View of the atoms in the Gold Foil Experiment
Rutherford's Gold Foil Experiment
Conclusions:
atom must contain a very small, dense center of positive charge
NUCLEUS
all the positive charge and 99.9% of the mass is in the nucleus
electrons define the space of an atom
electrons move at high speeds around the nucleus
atom does not have uniform density

29. Rutherford: 1909
After his Gold Foil Experiment, Rutherford modifies his model of the atom to contain 2 basic regions: a small dense positive nucleus (protons) with electrons outside.
Proposed a neutral part of the nucleus

30. Neils Bohr: 1913
Thought the atom was like the solar system (planetary model). Electrons orbit the nucleus with a fixed energy.
Energy Levels - analogous to rungs of a ladder
He wins the Nobel Prize for this model in It was eventually shown to be inaccurate and too simplistic.

31. Henry Moseley: 1913 Worked under Rutherford.
Using CRT’s he bombarded metals with electrons and observed the emitted X rays by the metals
Results: each metal produced X rays of unique frequencies or wavelengths (X ray spectral lines)

32. Moseley cont.
Conclusions: He determined that each element has a unique nuclear charge. Hence, a different number of protons (Atomic Number).
Each atom is electrically neutral and therefore has an equal number of electrons.
Killed by a sniper in WW in 1915

33. Chadwick won the Nobel Prize for his work in 1935.
James Chadwick: 1932
Studied under Rutherford.
1st isolated a neutron by bombarding beryllium atoms with alpha particles
He determined that the atom also contained a neutron which had approximately the same mass as a proton
Mass of proton = 1.673x10-24g
Mass of neutron = 1.675x10-24g
He proposed that the neutron had a neutral charge
Chadwick won the Nobel Prize for his work in 1935.

34. Wave (electron cloud) Model: 1924 to Present
Using Quantum Mechanics, the electron can be found in a probability region.

35. The atom through the ages…
FUN SONG
The atom through the ages…
The Atom Song
By Michael Ouffutt

36. Therefore: 
There are 3 subatomic particles: protons, neutrons and electrons. These are measured in “atomic mass units” (amu) as their mass is so small.
Subatomic
Particle
Mass (amu)
Location
Charge
Proton ( p+ )
1.673 x kg
( amu or 1 amu)
In the nucleus +
Neutron ( n0 )
1.675 x kg
( amu or 1 amu)
Electron ( e- )
9.1x kg
( amu or 0 amu)
Outside the nucleus -

37. Atomic Number and Mass Number
Atomic Number = the number of protons
Unique to each element
In a neutral atom, the number of protons equal the number of electrons.
Mass Number equal to the total number of protons + neutrons in the nucleus of an atom.
Ex) carbon-12

38. Shorthand way of representing an isotope of an element.
Isotopes
Atoms that have the same number of protons but a different number of neutrons (mass.)
Isotopic Notation
Shorthand way of representing an isotope of an element.
Ex) top number is the mass number (#p + #n)
bottom number is the atomic number (#p)
May also be written: chlorine-37 or Cl-37
The actual average atomic mass for all chlorine isotopes is amu

39. Isotopes of Hydrogen a. hydrogen (hydrogen – 1) 1p+ 0n0
b. deuterium (hydrogen – 2) 1p n0
c. tritium (hydrogen – 3) 1p n0
Isotope
Protons
Neutrons
Mass Number
Electrons
Isotopic Notation
Carbon-12 6 12
Carbon-13 7 13
Carbon-14 8 14

40. Ions Formed when an atom gains or loses an electron
a. Charge = # of protons - # of electrons
Ex) Mg +2 = lost 2 electrons
# of protons: 12 # of electrons: 10 Charge: +2
Positively Charged ion - CATION
Ex) N-3 = gained 3 electrons
# of protons: 7 # of electrons: 10 Charge: -3
Negatively Charged ion - ANION

42. Mg-25 12 13 25 10 +2 N-14 7 14 -3 Br-79 35 44 79 36 -1 Isotope Protons
Neutrons
Mass Number
Electrons
Isotopic Notation
Charge
Mg-25 12 13 25 10 +2
N-14 7 14 -3
Br-79 35 44 79 36 -1

43. Atomic Mass: Average Atomic Mass:
The mass of an atom expressed in amu (atomic mass units.)
One amu is equal to 1/12 the mass of a carbon-12 atom.
Average Atomic Mass:
The weighted average of all an element’s isotopes.
Mass Spectrometers are instruments used to measure masses of isotopes as well as their isotopic abundance.
This is the number shown in the box on the Periodic Table.
It is calculated by: (mass1 x %1) + (mass2 x %2) + …

44. Weighted Average Grade Example:
Straight Class
93% Tests
90% HW
70% Participation
84.3% Average
Weighted Class
x 70% =
x 20% =
x 10% =
Weighted
Average: 90.1%
Ex) carbon
C-12
C-13
C-14
? Straight
Average
13???
Actual Average
Atomic Mass =
amu
Ex) hydrogen
H-1
H-2
H-3
? Straight
Average
2???
Actual Average
Atomic Mass =
amu

45. Calculation of atomic mass
Magnesium has 3 naturally occurring isotopes:
78.99% Mg-24, 10.00% Mg-25, and
11.01% Mg-26
Calculate the atomic mass of magnesium.
(24 x ) = = 18.96
+ (25 x ) = =
+ (26 x ) = =
 amu

46. Calculation of atomic mass
Magnesium has 3 naturally occurring isotopes:
78.99% is amu
10.00% is amu
11.01% is amu
Calculate the atomic mass of magnesium.
( amu x )
+ ( amu x )
+ ( amu x )
24.31 amu

47. Question: Can we count atoms?
Atoms are too small to count or mass individually. It is easier to count many or mass many.
amu gram
(atomic scale) (macroscopic scale)
mole

48. Getting to know the terms…
MICROSCOPIC
Mass
MACROSCOPIC
Molar Mass
Atom
Atomic mass
amu
Element
g/mol
Molecule
Molecular mass
Molecular Compound
Formula Unit
Formula mass
Ionic Compound
Diatomic Molecules
H2 O2 F2 Br2 I2 N2 Cl2

49. Avogadro’s Number and the Mole
1) The mole is defined as the number of atoms in exactly 12 grams of carbon-12.
2) The number of particles in a mole is called Avogadro’s number. (6.02 x 1023)

50. MOLE RELATIONSHIPS 1 Mole = 6.02x1023 particles of substance
(atoms, formula units, molecules)
1 Mole = mass (g) of substance from PT

51. Mole Analogies
An Avogadro's number of standard soft drink cans would cover the surface of the earth to a depth of over 200 miles.
If you had Avogadro's number of unpopped popcorn kernels, and spread them across the United States of America, the country would be covered in popcorn to a depth of over 9 miles.
If we were able to count atoms at the rate of 10 million per second, it would take about 2 billion years
6.02 X 1023 Watermelon Seeds: Would be found inside a melon slightly larger than the moon.

52. Mole Analogies
6.02 X 1023 Donut Holes: Would cover the earth and be 5 miles (8 km) deep.
6.02 X 1023Pennies: Would make at least 7 stacks that would reach the moon.
6.02 X 1023 Grains of Sand: Would be more than all of the sand on Miami Beach.
6.02 X 1023 Blood Cells: Would be more than the total number of blood cells found in every human on earth.

53. What is atomic mass?
Mass of an atom
Carbon
12.0 amu
Oxygen
16.0 amu

54. What is molar mass?
Mass in grams of one mole of an element or compound, is numerically equivalent to the atomic mass of monatomic elements and the formula mass of compounds and diatomic elements. (Unit = g/mol)
Carbon
Atomic mass = 12.0 amu
Molar Mass = 12.0 g/mol
Magnesium
Atomic mass = 24.3 amu

55. Nuclear Energy

56. Nuclear Reactions: Change the composition of an atom’s nucleus.
2. The strong nuclear force holds the nucleus together.
3. Most atoms are stable
(equal number of p & n).
These are the smaller atoms
which are NOT radioactive.

57. 4. Unstable nuclei have more neutrons than
protons. These isotopes are radioactive.
5. As the elements become larger they become
more unstable.
6. All elements have at least 1 radioactive isotope. All the isotopes of those elements with atomic numbers greater than 83 are radioactive.
7. The larger nuclei are radioactive because
they have more neutrons than protons.

58. Suggests an architecture within the nucleus…Nuclear Shell Model
There are 265 stable nuclei
159 have even # of p+ & even # of n0
52 have even # of p+ and odd # of n0
50 have odd # of p+ and even # of n0
4 have odd #’s of both p+ and n0
Special stability if # of p+ or # of n0 or their sum = 2, 8, 20, 28, 50, 82, or 126 (MAGIC #’s)
Indicates stability of nucleus is greatest when nucleons are paired and exist in different energy levels (shells) in the nucleus
Suggests an architecture within the nucleus…Nuclear Shell Model

60. Unstable Nucleus

61. Characteristics of Subatomic Particles and Rays:
Mass (amu)
Charge
Symbol
Stopped by
Proton
Neutron
Beta Particle (electron)
Alpha Particle (He nucleus)
Gamma Ray +1
p+ or
paper
Few centimeters of lead
n0 or
Heavy clothing/Al foil -1 +2
paper
Several centimeters of lead

62. Nuclear Radiation Penetrating Power

63. Nuclear Radiation Penetrating Power

64. Spontaneous Emission of Radiation:
A. Unstable nuclei will spontaneously emit 3 types of natural radiation, this is also called radioactive decay.
B. When an atom emits 1 kind of radiation the original nucleus decomposes or decays to form a new nucleus and releases radiation. This is written in a nuclear equation.

65. Alpha & Beta Decay

66. 3 Types of Spontaneous Radiation:
A. Alpha Decay – spontaneous emission of
alpha particle from the nucleus.
B. Beta Decay – spontaneous emission of beta
particle from the nucleus
C. Gamma Decay – spontaneous emission of
gamma ray from the nucleus

67. Uranium Radioactive Decay Series

68. How Radon Gas Enters your House

69. Ways to Remove Radon Gas from Your Home

70. External view of a Radon mitigation system from a home basement.
Below is a view of the fan inside which runs 24 hours a day pulling air from under the basement floor.

71. Testing Methods for Radon

72. U.S. Radon Zones

73. Nuclear Bombardment Reactions:
A. Process in which a new element is formed by bombarding a nucleus with small energetic particles.
B. The energetic particle hits the nucleus and forms an unstable compound nucleus, which is short-lived.
C. This nucleus can emit another particle to stabilize itself.
D. This is the process used in particle accelerators where artificial isotopes and transuranium elements have been produced.
E. Sometimes referred to as “capture” in an equation.

74. Particle Accelerator in Switzerland with a 16.7 mile circumference

75. Nuclear Bombardment Reaction
target nucleus
ejected particle
new isotope (element)
projectile

76. Nuclear Fission
Process by which a heavy nucleus splits into two smaller nuclei.
Most fission reactions are induced.
The energy yield for fission reactions are very high.
Fission reactions are the source of energy used to generate electricity in nuclear power plants.
E. U-235 & Pu-239 are the radioisotopes used in reactors.

77. Nuclear Fission Reaction
temporary unstable nuclei that immediately splits
3 neutrons are produced which start additional fission reactions
Nuclear fuel
projectile – particle that starts the chain reaction
into 2 approximately equal mass product nuclei

78. F. In fission reactions, the product nuclei have far too
many neutrons, and are intensely radioactive. This
is considered radioactive waste.
G. The released neutrons can cause another reaction as
long as sufficient U-235 remains.
H. This is called a chain reaction.
I. The smallest amount (minimum volume) of
fissionable material needed to sustain a chain
reaction is called the critical mass.

79. Nuclear Chain Reaction
Fuel: U-235 or Pu-239
Critical mass for U is 110 lbs

80. Nuclear Fusion:
A. This is a thermonuclear reaction - requires high temperatures.
B. Occurs when two small nuclei fuse, or join, to form larger,
more stable nuclei.
C. Releases a large amount of energy.
D. Process that occurs on the sun and in a hydrogen bomb.
E. If fusion reactions are going to be practical, they need to
produce more energy than they require to get started.
F. In a fusion reaction, the starting materials are in a form of
plasma.
G. The biggest problem is obtaining the high temperatures
necessary for a fusion reaction to occur.
H. A “magnetic bottle” is used to hold plasma at high temperatures.

81. Nuclear Power Plants/A-bomb
Krypton-92
Fission
3 neutrons
Nuclear Power Plants/A-bomb
neutron
U-235
Energy
Barium-141
Fusion
The Sun/
H-bomb

82. The first Atomic Bomb is detonated at Trinity Site near Alamogordo, New Mexico on July 16, 1945.
shows the result of the blast.
A wooden house built 1km away from the test site…
A Monument stands at the test site today.

83. “Little Boy” Uranium fission bomb dropped on Hiroshima, Japan by the “Enola Gay” flown by Colonel Paul Tibbets

84. Hiroshima - August 6, 1945 Distance from Ground Zero (km) Killed
Injured
Population
 0 -1.0
86%
10%
  31,020
27%
37%
144,800 2%
25%
  80,300
Total
30%
256,300

85. Hiroshima 1945 & Today

86. Nagasaki - August 9, 1945 “Fat Man” – Plutonium Fuel
Distance from Ground Zero (km)
Killed
Injured
Population
 0 -1.0
88%
 6%
  30,900
34%
29%
144,800
11%
10%
  15,200
Total
22%
12%
173,800
“Fat Man” – Plutonium Fuel

87. U.S. Nuclear Testing
Large craters pockmark Frenchman Flats, Nevada, a former test site for U.S. nuclear weapons. The US conducted more than 1050 tests here and in Alaska, Colorado, Mississippi, New Mexico between 1945 and 1992.
The Soviet Union,
UK, France, China,
India and Pakistan
had a similar total
number of tests
over the same
time period.

88. Fusion Bombs
The first thermonuclear weapon (hydrogen bomb), code-named Mike, was detonated at Enewetak atoll in the Marshall Islands, Nov. 1, The photograph was taken at an altitude of 12,000 feet over 50 miles from the detonation site.

89. Only 6 countries have detonated a hydrogen bomb – US, UK, Soviet Union, France, China and India.
To obtain temperatures in the millions of degrees Celsius a fission reaction is set off first to start the fusion reaction.

90. Nuclear Reactors There are currently 111 commercial nuclear
power plants in the U.S. They provide 20%
of our country’s electricity, but 80% of the electricity used in southeastern PA.

91. B. There are 530 nuclear reactors in 30 nations around the world that provide 1/6 of the
world’s electricity. To produce electricity you need to turn a turbine. This can be accomplished by wind or water, must most commonly by steam. The only difference between a nuclear power plant and a conventional fossil fuel plant is the method used to produce boiling water.

92. 14. Parts of a Nuclear Reactor
Fuel Rods: Composed of 97% U-238 and 3%
U-235 (the fissionable isotope). Chalk- sized pellets are arranged in long steel cylinders in the reactor core. When the fuel has given up most of its energy it is called spent. It will be reloaded every 1 to 3 years. There can be 10,000,000 pellets in 1 plant.
B. Control Rods control the rate of a nuclear reaction. Without them the reaction would occur too fast for it to be effective.
C. Moderator is usually heavy water (D2O). Without sufficient cooling of the core a meltdown could occur. This water also shields workers.

93. View of fuel
rods and
control rods
immersed in
“heavy water.”

94. Parts of a Nuclear Reactor con’t.
D. Generator produces electricity by turning a steam turbine from the boiling water.
E. Cooling System: Water from outside is used to cool the steam (it does not come into contact with the cooling water in the core). Excess steam rises up in the cooling tower, condenses and falls back.
Cooling Towers
Limerick, PA

95. Nuclear Power Plant Diagram

96. Radioactive Waste:
A. Spent fuel rods have been accumulating for about 40 years. Spent fuel rods are highly radioactive,
with some isotopes remaining active for thousands of years. By federal law reactor waste must be
stored on site. The U.S. Government has not yet opened any permanent storage sites, but one called
Yucca Mountain in Nevada is currently being
negotiated. On-site storage is only a temporary measure, as tanks require too much maintenance
to be safe for long term storage.

97. Radioactive Waste
Radioactive waste is stored under water until it decays to lower levels.
Radioactive Warning Symbol

98. Temporary Radioactive Waste Storage
Waste is transferred to storage casks and stored on-site at each power plant.

99. Nuclear Accidents
Three Mile Island March 28, 1979 on the Susquehanna River near Harrisburg, PA. The worst nuclear accident in U.S. history was caused by technical failures and human error. About 2 million people were exposed to 1mrem of radiation which led to no deaths or injuries.

100. Nuclear Accidents
Chernobyl April 26, 1986 in the northern Ukraine. The core melt meltdown caused radioactive materials to spread over a wide area of Europe. Officials at a Sweden Nuclear Power Plant 1st noticed that radioactive particles were on their clothes and thought their own plant was malfunctioning. The worst nuclear accident in the world was caused by a flawed reactor design and inadequately trained operators.

101. 57 immediate deaths with 4000 additional cancer deaths long term
57 immediate deaths with 4000 additional cancer deaths long term. Over 360,000 people were evacuated permanently from the area which remains closed. The initial cover-up of the incident made clean up worse.

102. Nuclear Accidents Japan 2011
An earthquake and resulting tsunami caused the reactors at the Fukushima plant in Japan to lose power. Without power and functioning back-up generators, the core in three reactors overheated and melted. Multiple explosions, fires, and gas releases complicated the problem. Also, contaminated water was released into the environment. People were forced to evacuate, and clean-up is still underway.

103. Uses for Nuclear Chemistry:
A. Half life
1. The time required for ½ of the atoms of a radioactive isotope to decay.
2. Using radioactive isotopes to determine the age of an object is called radio carbon dating.
Ex. If I have 1.00 mg of , which has a ½ life of 8.04 days, how much will be left after 1 half-life? After 2? After 3?

104. B. Radioactive Isotopes and Dating
1. All animals and plants contain carbon-14.
2. Even though carbon-14 undergoes radioactive decay, it is constantly replenished during a lifespan.
3. The half-life of carbon-14 is 5730 years.
4. The ratio of C-12 to C-14 is compared to
another object of a similar age.
5. Cannot use carbon-14 dating with objects
that never lived.

105. 6. After 4 half lives, the amount of carbon-14 remaining is too small to give reliable data.
7. Carbon-14 is not useful for specimens over 25,000 years old, so Potassium-40
is used instead. It has a half-life of 1.28 billion years.

107. Radioactive Decay of Strontium-90
28 years
What is the ½ Life of Strontium-90???
How long until no more Strontium-90 remains?

108. What is the ½ Life of this Radioactive Sample?
2 days

109. Smoke Detectors:
1. Smoke detectors emit a small amount of alpha particles.
2. When smoke particles mix with the gas, they slow the current flow setting off the alarm.

110. Medical Uses
1. CAT SCAN – the body is analyzed using X-rays.

111. 2. MRI and NMR – detects body’s absorption of radio waves.

112. 3. PET – Measures gamma rays from certain part of the brain.

113. 4. Radioisotopes prepared in a nuclear reactor can be used to both treat and detect various medical conditions. Tracers can be used to follow a particular isotope through its normal path in the body to show any abnormalities.
Ex) Upper and Lower GI uses radioactive Barium to detect stomach and intestinal problems. An IVP measures the bodies absorption of radioactive iodine to detect kidney stones.

114. 5. Irradiation can be used as an energy source to treat cancer
5. Irradiation can be used as an energy source to treat cancer. The diseased area is exposed to ionizing radiation to kill cancerous cells.
Ex) Ingest large amounts of I-131 kills thyroid cancer, External beam of Co-60 can be directed at a cancerous spot. Irradiation can also be used to sterilize medical instruments and preserve food.
Food Irradiation Symbol

115. Exposure to Radioactivity:
A. Continued exposure to radiation is dangerous; therefore, people working in these conditions must monitor their exposure to radiation.
B. People working with radiation wear film badges to monitor their exposure.

116. C. A dosimeter measures radiation in people, a
Geiger Counter measures radiation of objects.
D. Radiation is usually measured in units of mrems. Higher doses for a longer period of time over a large area cause the most damage, especially for rapidly dividing cells like sex cells and blood cells.

117. Sources of Our Radiation Exposure