teacher notes: ch 17 nuclear chemistry
TRANSCRIPT
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Teacher Notes: Ch 17
Nuclear Chemistry
2
Ch 17.1-17.2
Topic:Radioactivity
EQ: How was
radioactivity discovered
and what is it?
3 Ch 17.1 • Some isotope’s are not stable.
• The emitted subatomic particles are
called nuclear radiation.
• The isotopes that emit them are termed
radioactive.
• Nuclear radiation can be harmful -
damage biological molecules.
• But not all Radioactive isotopes are
harmful.
4
• In 1895 William Roentgen discovered X-
rays, a form of radiation.
Ch 17.2: The Discovery of Radioactivity
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• In 1896, French scientist Antoine-Henri Becquerel (1852–1908), discovered radioactivity.
• He studied Uranium minerals that emit light after being exposed to sunlight, a phenomenon called phosphorescence.
Ch 17.2: The Discovery of Radioactivity
6
• Marie Curie (1867–1934), one of
the first women in France to
attempt doctoral work by studying
uranic rays for her doctoral thesis.
• Her first task was to determine
whether any other substances
besides uranium emitted rays.
• In 1898, Marie Curie and her
husband Pierre (1859–1906) took
Becquerel’s mineral sample (called
pitchblende) and isolated the
components emitting the rays.
Ch 17.2 The Discovery of Radioactivity
7 The Discovery of Radioactivity:
Marie Curie
• In 1903, Curie received the Nobel Prize
in physics for the discovery of
radioactivity.
• Curie discovered two new elements.
Curie named one of her newly discovered
elements polonium after her home
country of Poland.
8 • Curie named the 2nd element
Radium because of the very
high amount of radioactivity
that it produced.
• Radium was so radioactive that
it glowed in the dark and
emitted significant amounts of
heat.
• In the past, radium was added
to some paints (watch dials that
made the dial glow)
9 The Discovery of Radioactivity
• In 1911, Curie was awarded a second
Nobel Prize, this time in chemistry, for
her discovery of the two new elements
polonium and radium.
• She is the first woman to win the
Nobel Prize and is the only person to
receive Nobel Prizes in two different
sciences – physics and chemistry!!!
• Element 96 (curium) is named in
honor and her contributions to our
understanding of radioactivity.
10 An Unstable System
• The rays and particles emitted by a
radioactive source are called radiation.
• REMEMBER…..Isotopes are atoms of the
same element that have different numbers
of neutrons and mass number.
• Isotopes of atoms with unstable nucleus
are called radioisotopes.
11
1. Marie Curie discovered that chemical
Reactions were affected by Pressure and
Temperature, whereas nuclear reactions were not
affected by P and T.
2. Chemical Reactions involve electrons, not
protons and neutrons.
3. Nuclear reactions involve the nucleus;
changes protons & neutrons .
– THIS CHANGES THE IDENTITY OF
ELEMENT!!!!
Nuclear Reactions vs. Chemical Reactions
(3 differences - Muy Importante!!!)
12
Ch 17.3-17.4
Topic: Types of
Radiations
EQ: What are the different
types of radioactive
decay?
13 Ch 17.3:
Main Types of Radiation
• Five Types:
–Alpha (α)
–Beta (β)
–Gamma (γ)
–Positron
–Electron Capture
14 Radioactivity
Radioactivity is
the emission of
tiny, energetic
particles by the
nuclei of certain
unstable atoms.
Nuclei are
unstable when
they are too large
or contain an
unbalanced ratio of
neutrons to
protons.
Draw with notes
15 Isotope Notation
Any isotope can be represented with the following
notation:
The main subatomic particles—protons, neutrons,
and electrons—can be represented with similar
notation.
•FYI - Proton – usually
referred to as hydrogen H1
1
16
Types of Radiation
He4
2
• Alpha (ά) – a positively
charged helium isotope
•Beta (β) – an electron
•Gamma ray (γ) – pure
energy 00
0
−1 e 0
−1 or
17 Other Nuclear Particles
• Positron – a positive electron
•Electron capture
0
+1 e 0
+1 or
e 0
−1
18 Nuclear Equations
• A nuclear equation represents the changes that occur
during radioactivity.
• Example:
• The term nuclide is used in nuclear chemistry to
mean a specific isotope.
• The original atom is called the parent nuclide, and
the products are called the daughter nuclides.
19 Nuclear Equations Must Be Balanced
• Check your work…..
The sum of the atomic numbers on both sides of
a nuclear equation must be equal, and the sum of
the mass numbers on both sides must also be
equal.
20
• Penetrating power is the ability to penetrate matter.
In order for radiation to damage important molecules
within living cells, it must penetrate the cell.
Penetrating Power
21 Alpha Radiation
Alpha (α) Radiation occurs when an unstable
nucleus emits an α particle composed of 2 protons
and 2 neutrons.
22
Alpha Radiation (α)
• helium nucleus
• charge is 2+
charge
Mass #
4 4 +2 4
2 2 2 He He
23
• Alpha radiation: most massive of all particles.
– Has the lowest penetrating power
• Alpha radiation - can be stopped by a sheet
of paper, by clothing, or even by air.
24
Alpha Decay
+ +
+ +
+ +
210
84 Po
+ +
Particle
210
84 Po +
LEFT side
25 Writing Nuclear Equations
• Alpha Decay of Th – 232….
LEFT side
26
Alpha Decay
U 238
92 He
4
2 +
Types of Radioactive Decay LEFT side
27
Alpha Decay
Pu 239
94 +
Types of Radioactive Decay
U 234
92 +
LEFT side
28
Beta radiation occurs when an unstable nucleus
emits an electron.
29
Beta Radiation
• A Beta particle is a very-fast moving electron
Charge
Mass #
0
−1
30
• Beta radiation:
– much less massive than alpha particles
– have greater penetrating power
– a sheet of metal (like foil) or a thick piece of
wood is required to stop them.
31
Beta Decay
14
6 C
-
Particle
+ +
+ +
+ + + +
+ +
+ + +
+ -
+ 14
6 C
LEFT side
32
I 131
53 + e
0
−1
Beta Decay
Types of Radioactive Decay LEFT side
33
Beta Decay
He 6
2 +
Na 25
11 +
LEFT side
34 Gamma (γ) Radiation
• Different from alpha or beta radiation.
• Gamma radiation is not matter but
electromagnetic radiation.
• Gamma rays are high-energy (short-
wavelength) photons (bundles of light).
• A gamma ray has no charge and no mass.
35 Gamma (γ) Ray Radiation Damage Potential
• Gamma rays:
– Highest penetrating power.
– Stopping gamma rays requires several
inches of lead shielding or thick slabs of
concrete.
36
Radiation Draw LEFT side
37
Penetrating Ability
38
Positron emission occurs when an unstable
nucleus emits a positron (positive electron).
39
• The symbol for a positron is:
• Positron - same mass as an electron but
opposite charge.
• Positron emission is similar to beta emission in
its penetrating power.
40
C
11
6 + e
0
1
Positron Emission
Types of Radioactive Decay LEFT side
41
• Electron capture occurs when the nucleus of an atom draws in a surrounding electron.
• Written on left side of rxn!!
Positron emission and electron capture
e0
1
42 Table 17.1 Selected Types of Radioactive Decay
Draw LEFT side – Great Summary of radiations
43
Balancing a Nuclear Equation
• Write a balanced nuclear equation for the alpha decay of gold-230.
LEFT side
44
Question 2
What element is formed when silver - 110
radioisotope undergoes alpha decay?
LEFT side
45
Question 3
What element is formed when undergoes
a. beta decay?
b.Positron decay?
LEFT side
46
Question 4
What element is formed when undergoes
a. neutron decay?
b.electron capture decay?
LEFT side
47
Checking for Understanding
238 234 234 234 230U Th Pa U Th ?
LEFT side
48
Ch 17.5
Topic: Detecting
Radiations and Half life
EQ: How is radiation
detected?
49 Detecting Radioactivity
• Film-badge dosimeters consist
of photographic film held in a
small case that is pinned to
clothing.
• The badges are collected and
processed as a way to monitor
exposure to radiation.
• The more exposed the film has
become, the more radioactivity
to which the person has been
exposed.
50 Geiger-Müller Counter
• Energetic particles emitted by
radioactive nuclei pass through a
chamber filled with argon gas and
ionize (create ions) it.
• Creating a tiny electrical current
between the + and - charges.
• This electrical signal can be
detected on a meter.
• The “Clicking” is the sound most
people associate with a radiation
detector.
51 The Concept of Half-Life
• The time it takes for half of the parent nuclides
in a radioactive sample to decay to the
daughter nuclides is called the half-life.
– One half-life is always ½ of what was
present at the start.
– Two half-lives is ¼ of what was present at
the start.
– Three half-lives is 1/8 of what was present
at the start.
52 Different Nuclides Decay at Different Rates
• Thorium-232 has a half-life of 1.4 × 1010, or 14 billion years.
• Radon-220 has a half-life of approximately 1 minute.
53 Illustration of Half-Life
54
Ch 17.7-17.10
Topic: Fission vs. Fusion
EQ: How is radiation
important to us and how
is it harmful to us?
55 Chemistry and Health: Environmental Radon
• Radon—a radioactive gas.
• Radon can attach to dust particles and then be
inhaled into the lungs, where it could increase
lung cancer risk.
• The radioactive decay of radon is by far the
single greatest source of human radiation
exposure.
• Radon-222 has a half-life of 3.8 days.
56 Map of the United States Showing Radon Levels
• Excessively high
indoor radon levels
require the installation
of a ventilation system
to purge radon from
the house. Lower
levels can be
ventilated by keeping
windows and doors
open.
Zone 1 counties have the highest levels, and zone 3
counties have the lowest.
57 The Discovery of Nuclear Fission: Fermi’s Role
• In the mid-1930s, Enrico
Fermi (1901–1954), an
Italian physicist, tried to
synthesize a new element by
bombarding uranium with
neutrons.
• The element with atomic
number 100 is named
fermium, in honor of Enrico
Fermi.
58 Nuclear Fission Reported
On January 6, 1939, Scientists reported that the
neutron bombardment of uranium resulted in
nuclear fission—the splitting of the atom.
59 History of the Atomic Bomb
• U.S. scientists realized that uranium enriched with U-
235 could undergo a chain reaction. The result would
be a self-amplifying reaction capable of producing an
enormous amount of energy—an atomic bomb.
• Several U.S. scientists persuaded Albert Einstein to
write a letter to President Franklin Roosevelt warning
of the possibility of Germany constructing an atomic
bomb.
• In 1941, Roosevelt assembled the resources for the top-
secret Manhattan Project. Its main goal was to build an
atomic bomb before the Germans did.
• The project was led by physicist J. R. Oppenheimer
(1904–1967) and was headquartered at the high-
security research facility in Los Alamos, New Mexico.
60 History of the Atomic Bomb
• Four years later, on July 16, 1945, the world’s first
nuclear weapon was tested New Mexico. The first
atomic bomb exploded with a force equivalent to
18,000 tons of dynamite.
• Meanwhile, the Germans had not been successful in
making a nuclear bomb.
• Instead, the atomic bomb was used on Japan. One
bomb was dropped on Hiroshima, and a second bomb
was dropped on Nagasaki. Together, the bombs killed
approximately 200,000 people and forced Japan to
surrender.
• World War II was ended.
61 The Testing of the World’s First Nuclear Bomb at Alamogordo,
New Mexico, in 1945
62 Nuclear Power: Using Fission to Generate Electricity
• A nuclear-powered electrical
plant can produce a lot of
electricity with a small
amount of fuel.
• Nuclear power plants generate
electricity by using fission to
generate heat.
• The heat is used to boil water
and create steam, which turns
the turbine on a generator to
produce electricity.
• The fission reaction occurs in
the nuclear core of the power
plant, or reactor.
63 Problems at Chernobyl Nuclear Power Generator
• Fission reaction occurring in a nuclear power plant can overheat.
• This type of accident occurred in Chernobyl in the former Soviet Union on April 26, 1986.
• The nuclear core overheated and began to burn.
• The accident caused 31 deaths directly and produced a fire that scattered radioactive debris into the atmosphere, making the surrounding countryside uninhabitable. The overall death toll from subsequent cancers is undetermined at this time.
• Reactor cores in the United States are not made of graphite and could not burn in the way that the Chernobyl core did.
64 Problems at Fukushima Nuclear Power Generator
• Another accident occurred at the Nuclear Power Plant
in Japan in March of 2011. (5 years ago)
• A 9.0 magnitude earthquake triggered a tsunami that
flooded the coastal plant and caused the plant’s
cooling system pumps to fail.
• Several of the nuclear cores within the plant
overheated (fuel gets so hot that it melts).
• The release of radiation into the environment, while
significant, was lower in Japan than at Chernobyl.
• The cleanup of the site, however, will continue for
many years.
65 Some Problems with Nuclear Power Generation
Waste Disposal
• The amount of nuclear fuel used in electricity
generation is small compared to that of other
fuels
• The products of the reaction are radioactive and
have very long half-lives (thousands of years or
more).
• Currently, in the United States, nuclear waste is
stored on site at the nuclear power plants.
• A permanent disposal site was being developed
in Yucca Mountain, Nevada.
66 Nuclear Fusion: The Power of the Sun
• Nuclear fusion is the combination of two light
nuclei to form a heavier one.
• Nuclear fusion is the basis of nuclear weapons
called hydrogen bombs. A modern hydrogen
bomb has up to 1000 times the explosive force
of the first atomic bombs. These bombs
employ the following fusion reaction:
67 The Effects of Radiation on Life
Radiation Damage
• The high levels of radiation kill large numbers of cells.
• People exposed to high levels of radiation have weakened
immune systems and a lowered ability to absorb nutrients from
food.
• In milder cases, recovery is possible with time.
• In more extreme cases, death results, often from infection.
68 The Effects of Radiation on Life
Increased Cancer Risk
• Lower doses of radiation over extended periods of time
can increase cancer risk because radiation can damage
DNA.
• Changes in DNA can cause cells to grow abnormally
and to become cancerous.
• Cancerous cells grow into tumors that can spread and,
in some cases, cause death.
• Cancer risk increases with increased radiation exposure.
69 The Effects of Radiation on Life
Genetic Defects
• Another possible effect of radiation exposure is
genetic defects in offspring.
• If radiation damages the DNA of reproductive cells—
such as eggs or sperm—then the offspring that
develop from those cells may have genetic
abnormalities.
70 Radioactivity in Medicine
• An isotope scan Technetium-
99 is often used as the
radiation source for bone
scans.
• Phosphorus-32 is used to
image tumors because it is
preferentially taken up by
cancerous tissue.
• Iodine-131 is used to diagnose
thyroid disorders.