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Honors Chapter 25 Powerpoint

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Honors Chapter 25 Powerpoint
Chapter 25: Nuclear
Chemistry
25.1: Nuclear
Radiation
• Marie Curie (1867-1934) and
Pierre Curie (1859-1906) were
able to show that rays emitted
by uranium atoms caused
fogging in photographic plates.
• Marie Curie named the process
by which materials give off such
rays radioactivity.
• The penetrating rays and
particles emitted by a radioactive
source are called radiation.
• Nuclear reactions differ from
chemical reactions in a
number of important ways.
• In chemical reactions, atoms
tend to attain stable electron
configurations by losing or
sharing electrons.
• In nuclear reactions, the nuclei of
unstable isotopes, called
radioisotopes, gain stability by
undergoing changes.
25.1
Radioactivity
• An unstable nucleus releases
energy by emitting radiation
during the process of
radioactive decay.
25.1
• The three main types of
nuclear radiation are
alpha radiation, beta
radiation, and gamma
radiation.
25.1 Radiation
• Alpha
• Alpha radiation consists of
helium nuclei that have been
emitted from a radioactive
source. These emitted particles,
called alpha particles, contain two
protons and two neutrons and
have a double positive charge.
• Beta Radiation
• An electron resulting
from the breaking apart
of a neutron in an atom is
called a beta particle.
25.1
Types of
Radiation
• Gamma Radiation
• A high-energy photon emitted
by a radioisotope is called a
gamma ray. The high-energy
photons are electromagnetic
radiation.
25.1
Types of Radiation
• Alpha particles are the least
penetrating. Gamma rays
are the most penetrating.
25.1
Types of Radiation
25.1 Section Quiz.
• 1. Certain elements are
radioactive because their atoms
have
a) more neutrons than
electrons
b) an unstable nucleus.
c) a large nucleus.
d) more neutrons than protons.
25.1 Section Quiz.
• 2. An unstable nucleus
releases energy by
a) emitting radiation.
b) thermal vibrations.
c) a chemical reaction.
d) giving off heat.
25.1 Section Quiz.
• 3. Which property does
NOT describe an alpha
particle?
a) 2+ charge
b) a relatively large mass
c) a negative charge
d) low penetrating power
25.1 Section Quiz.
• 4. When a radioactive
nucleus releases a highspeed electron, the process
can be described as
a) oxidation.
b) alpha emission.
c) beta emission.
d) gamma radiation.
25.2 Nuclear
Transformations
• The nuclear force is an
attractive force that acts
between all nuclear particles
that are extremely close
together, such as protons and
neutrons in a nucleus
• At these short distances, the
nuclear force dominates
over electromagnetic
repulsions and hold the
nucleus together.
25.2
25.2
Nuclear Stability and Decay
• Too few or too many neutrons
cause decay.
• A positron is a particle with
the mass of an electron but a
positive charge. During
positron emission, a proton
changes to a neutron.
25.2
Nuclear Decay Practice
•
12
5B
→
12
6C
+ ____
• 22589Ac → 22187Fr + ____
•
63
28Ni
→ ____ +
0
-1e
• 21283Bi → ____ + 42He
Complete the Equations
• 2713Al + 42He → 3014Si + ____
• 21483Bi → 42He + ____
•
27
•
66
14Si
→
29Cu
0
→
-1e
66
+ ____
30Zn
+ ____
Practice
214
83Bi
• 1)
produces β
237
• 2) 93Np produces α
116
• 3) 47Ag produces β
211
• 4) 83Bi produces α
Practice
• Write a balanced nuclear
reaction for the reaction in
which oxygen-15 undergoes
positron emission.
• Write the balanced nuclear
equation for the electron
capture of rubidium-81.
25.2
Half-Life
• A half-life (t1/2) is the time
required for one-half of the
nuclei of a radioisotope
sample to decay to products.
• After each half-life, half of
the existing radioactive
atoms have decayed into
atoms of a new element.
for Sample Problem 25.1
Practice Problems
1. A 0.456 mg sample of hydrogen-3
was collected. After 24.52 years,
0.114 mg of the sample remains.
What is the half-life of hydrogen-3?
2. Strontium-90 has a half-life of 29
years. What is the mass of
strontium-90 in a 5.0g sample at
the end of 87 years?
Half-life Practice
3. The half-life of iodine-131 is
8.1 days. How long would it
take for ¾ to decay?
4. Radon-222 has a half-life of
3.82 days. How long would it
take for 15/16 to decay?
Half-Life Practice
• 5. A radioisotope has a half-life of 4
days. How much of a 20-gram
sample of this radioisotope remains at
the end of 4 days? 8 days?
• 6. The mass of cobalt-60 in a sample
has decreased from 0.8 g to 0.2 g
over a period of 10.5 years. Calculate
the half-life of cobalt-60.
Half-life Formula
•
•
•
•
N = N0(1/2)n
N is the remaining amount
N0 is the initial amount
n is the number of half lives that
have passed
Half-life
• The half-life of tritium is 12.3 y.
If 48.0 mg of tritium is released
from a nuclear power plant
during the course of a mishap,
what mass of the nuclide will
remain after 49.2 y? After 98.4
y?
Half-life
• An unknown radioisotope
exhibits 8540 decays per
second. After 350 min, the
number of decays has
decreased to 1250 per second.
What is the half-life?
Half-life
• The table shows the amounts of
radioisotopes in three different samples.
To the nearest gram, how much will be
in Sample B and Sample C when
Sample A has 16.2 g remaining?
Sample
Radioisotope
Half-life
Amount (g)
A
Cobalt-60
5.27 y
64.8
B
Tritium
12.32 y
58.4
C
Strontium-90
28.79 y
37.6
25.2
Transmutation Reactions
• The conversion of an atom of
one element to an atom of
another element is called
transmutation.
• Transmutation can occur by
radioactive decay or when
particles bombard the nucleus
of an atom.
•The elements in the periodic
table with atomic numbers
above 92, the atomic
number of uranium, are
called the transuranium
elements.
• None of the transuranium
elements occur in nature, and
all of them are radioactive.
25.2
25.2
Transmutation Reactions
• Transuranium
elements are
synthesized in
nuclear reactors and
nuclear
accelerators.
Transuranium
• Write a balanced nuclear
equation for the induced
transmutation of oxygen-16 into
nitrogen-13 by proton
bombardment. An alpha
particle is emitted from the
nitrogen atom in the reaction.
Einstein’s equation
• ∆E = ∆mc2
• ∆E is the change in energy in
Joules, m is mass in kg, c is the
speed of light in m/s
• A small change in mass results in a
large change in energy
Mass defect and binding
energy
• The mass of the nucleus is always less
than the sum of the masses of the
individual protons and neutrons that
comprise it.
• Mass defect – difference in mass
between a nucleus and its component
nucleons
Mass defect and binding
energy
• Nuclear binding energy –
energy needed to break one
mole of nuclei into individual
nucleons
• the larger the binding energy,
the more strongly the
nucleons are held together
Calculating Mass Defect
•
•
•
•
•
•
•
Mass defect = mnucleus – [Npmp + Nnmn]
mnucleus is the mass of the nucleus
mp is the mass of a proton
mn is the mass of a neutron
Np is the number of protons
Nn is the number of neutrons
The mass defect is then used in
Einstein’s equation to determine energy
Calculating mass defect
• Calculate the mass defect and
binding energy of lithium-7.
The mass of lithium-7 is
7.016003 amu.
• Use 1.007825 amu for mp
and 1.008665 amu for mn
25.2 Section Quiz.
• 1. When potassium-40 (atomic
number 19) decays into calcium40 (atomic number 20), the
process can be described as
a) positron emission.
b) alpha emission.
c) beta emission.
d) electron capture.
25.2 Section Quiz.
• 2. If there were 128 grams
of radioactive material initially,
what mass remains after four
half-lives?
a) 4 grams
b) 32 grams
c) 16 grams
d) 8 grams
25.2 Section Quiz.
• 3. When transmutation
occurs, the ________ always
changes.
a) number of electrons
b) mass number
c) atomic number
d) number of neutrons
25.2 Section Quiz
• 4. Transmutation occurs by
radioactive decay and also by
a) extreme heating.
b) chemical reaction.
c) high intensity electrical
discharge.
d) particle bombardment of
the nucleus.
25.3 Fission and
Fusion of Atomic
Nuclei
25.3
Nuclear Fission
• When the nuclei of certain
isotopes are bombarded
with neutrons, they undergo
fission, the splitting of a
nucleus into smaller
fragments.
25.3
Nuclear Fission
• In a chain reaction, some of
the neutrons produced react
with other fissionable atoms,
producing more neutrons
which react with still more
fissionable atoms.
25.3
Nuclear Fission
• 2 ways to slow down reactions:
• Neutron moderation is a
process that slows down
neutrons
• Neutron absorption
decreases the number of
neutrons using control rods
25.3
Nuclear Waste
• Water cools the spent rods, and
also acts as a radiation shield to
reduce the radiation levels.
Nuclear Fusion
• Fusion occurs when nuclei combine
to produce a nucleus of greater mass.
In solar fusion, hydrogen nuclei
(protons) fuse to make helium nuclei
and two positrons.
25.3
Nuclear Fusion
• Fusion reactions, in
which small nuclei
combine, release
much more energy
than fission
reactions, in which
large nuclei split.
25.3
Nuclear Fusion
• The use of controlled fusion as an
energy source on Earth is appealing.
• The potential fuels are inexpensive
and readily available.
• The problems with fusion lie in
achieving the high temperatures
necessary to start the reaction and
in containing the reaction once it
has started.
25.3 Section Quiz.
• 1.
One of the control mechanisms
for a sustainable nuclear chain
reactor involves slowing down the
released neutrons so they may be
captured by other nuclei. This is done
using
a) moderators.
b) shielding.
c) absorbers.
d) control rods.
25.3 Section Quiz.
• 2. Choose the correct
words for the spaces. In solar
fusion, _______ nuclei fuse to
form _______ nuclei.
a) helium, hydrogen
b) hydrogen-1, hydrogen-2
c) hydrogen, helium
d) hydrogen-1, hydrogen-3
25.4 Radiation in Your
Life
25.4
Detecting Radiation
• Ionizing radiation is
radiation with enough
energy to knock electrons off
some atoms of the bombarded
substance to produce ions.
−Devices such as Geiger
counters, scintillation counters,
and film badges are commonly
used to detect radiation.
25.4
Detecting Radiation
• Radiation can produce ions, which
can then be detected, or it can expose
a photographic plate and produce
images.
• Radioactive
particles and
rays vary greatly
in penetrating
power
25.4
Detecting Radiation
• Geiger Counter
• A Geiger counter
uses a gas-filled
metal tube to
detect radiation.
25.4
Detecting Radiation
• Scintillation Counter
• A scintillation
counter uses a
phosphor-coated
surface to detect
radiation.
25.4
Detecting Radiation
• Film Badge
• A film badge
consists of several
layers of
photographic film
covered with black
lightproof paper, all
encased in a plastic
or metal holder.
25.4
Using Radiation
• Radioisotopes can be used to
diagnose medical problems
and, in some cases, to treat
diseases.
25.4
Using Radiation
• This scanned image
of a thyroid gland
shows where
radioactive iodine131 has been
absorbed.
25.4 Section Quiz.
• 1. Ionizing radiation can
remove _______ from atoms.
a) protons
b) neutrons
c) positrons
d) electrons.
25.4 Section Quiz.
• 2. Which of the following is
NOT a device used to detect
radiation?
a) Geiger counter
b) scintillation counter
c) film badge
d) radioisotope
25.4 Section Quiz.
• 3.
Choose the correct words for the
space. When a tumor is treated by
radiation, more cancer cells than normal
cells are killed because cancer cells
____________ than normal cells.
a) are more susceptible to damage
because they grow faster
b) absorb more radiation because they
are larger
c) grow slower
d) are smaller
25.4 Section Quiz.
• 4. How do scientists detect
thyroid problems?
a) with teletherapy
b) by neutron activation analysis
c) using an iodine-131 tracer
d) using a radioisotope sealed in
a gold tube
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