Nuclear Chemistry Notes
•
Changes in matter originating in the ________________ of an atom
• All atoms have• p+ and n0 (______________: particles that make up the nucleus)
• p+ number is the atomic number = ____
• p+ + n0 = mass number = ____
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The Nucleus



is the nucleus of an atom having a specific atomic number and atomic mass #
Isotopes: Elements with the same atomic ____, but ____________ mass ____ due to gaining or losing
of neutrons
Ex:There are three naturally occurring isotopes of uranium:
o Uranium-234
-Uranium-235 Uranium-238

Radioactivity
 It is not _________ for some nuclides of an element to be __________, or ________________.
 We refer to these as __________________
 _____________ are unstable & spontaneously emit particles & electromagnetic ___________(EM)
 __________________- atoms containing these radionuclides
 __________________- process by which one element is converted to another element by the spontaneous
emission of radiation

Large Nuclei
 Nucleus is held together by _______________
 Large nuclei tend to be ____________ because the force is not strong enough to hold it together
 These nuclei break apart and ____________
 All nuclei with ____ or more protons are radioactive
 Almost all elements with more than 92 protons don’t exist _____________

Neutron to Proton Ratios
 Any element with more than one proton (i.e., anything but
hydrogen) will have repulsions between the protons in the nucleus.
 A strong _________ ________ helps keep the nucleus together.
 Neutrons play a key role stabilizing the nucleus.
 Therefore, the ratio of neutrons to protons is an important factor.
 For smaller nuclei (Z  20) stable nuclei have a neutron-to-proton
ratio close to 1:1.
 As nuclei get larger, it takes a greater number of neutrons to
stabilize the nucleus.

What is Radioactivity?
• When an ___________ nucleus emits one or more particles or ____________
• When these particles are emitted, the element changes to another ___________or to a
different_____________
• Nuclear _____________ refers to radiation resulting from nuclear changes

Types of Nuclear Radiation:

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Alpha ()
• Symbol is________________
•
Actually particles made of ___ p+ and ___ n0, same as a He nucleus
• +2 charge, most ____________ of all nuclear radiation, mass = 4 amu
• Do not travel far, can be stopped by a sheet of ________________
• Can be very dangerous inside _____________ body – illness and disease
Beta ()
• Symbol is Greek letter, ___________ (β)
• High speed _______________ charged particles that come from the nucleus – hmmm…
• ___________ (neutral) actually decays to form a p+ and an e-, e- is ejected from nucleus
• Travel farther than α, but can be stopped by 3 mm of _____, or 10 mm of wood
• Can cause damage _________ cells
Gamma ()
• Not made of ___________, no charge or mass
• Waves of high electromagnetic energy (photons)
• Usually emitted from nucleus when alpha or beta decay occurs
• A _________ de-excites by emitting a high energy gamma ray photon
• High energy, can be stopped by 60 cm of Al or 7 cm of Pb
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Nuclear (Radioactive) Decay
 When unstable nuclei emit alpha or beta particles, what changes?
– Number of protons or neutrons
– New ______________ or new atomic _______________
1. The ____________ of the mass numbers on the ___________ side must be the same as the total of
the mass numbers on the ____________ side
2. The total of the _________ ______________ on the reactant side must be the same as the total of
the atomic numbers on the product side
Alpha Decay, alpha particle production
•
•
Nucleus gives up 2 ______ and 2 _______
All ___________________ add up, all atomic numbers ______ up
Change During Beta Decay,(emission)
 Neutron is changed to a _________________ and an _______________ and emitted
 __________________ atomic number due to conversion of a neutron to a proton and an electron
 So neutron is lost and proton is _________________
Beta Decay
Ex:
131
53
I
→
131
54
Xe +
0
1
e
(or
0
1
)
Gamma Radiation

Loss of a -ray (_______-energy radiation that almost always accompanies the loss of a nuclear particle)
238
92
U
→
234
90
Th
+
4
2
He
+  (gamma ray)
0
0
Measuring Radioactivity
One can use a device like this __________ _______________ to measure the amount of activity present in a
radioactive sample.
• When radioactive particles move through air, they collide with molecules of gases & split them apart into
•
•
______________ and positively charged ______. This is called ____________________.
The ions created by radiation, will conduct a _____________ that is detected by the instrument.
Decay Rates
• ___________-________ = the time in which half a radioisotope’s nuclei to decay into products
• After 1 half-life, ___________ of the substance is unchanged
• After 2 half-lives, ________ of the substance is unchanged
Half- Life
• Measure how quickly a substance _______________
• Can be anywhere between nanoseconds to billions of years, depending on nuclear __________________
• C-14 is used to find the age of relatively recent materials
• C-14 is taken in in tiny fractions while alive in some molecules of CO2
• C-14 goes through beta decay, so ratio is compared in __________ and _______________ things
Example Problem:
The half-life of iodine-131 is 8 days. If you start with 36 grams of I-131, how much will be left after 24 days?
Nuclear Fission & Fusion
Nuclear Fusion
• Energy can be obtained when 2 lighter nuclei (elements) _________ together to form a ___________
(more stable) nucleus
• Occurs in stars, including our sun, energy is produced when _____________ nuclei undergo fusion and
release TREMENDOUS amounts of energy
Fusion in the Sun
• Multi-step process where ______ different isotopes
of hydrogen fuse ________________ to form a helium
nucleus and energy in form of gamma rays
Nuclear Binding Energy of He
• The mass of a _________ nucleus, 4.0015 amu, is less than that of 2 protons & 2 neutrons, 4.032 amu. The
energy equivalent of the .0305 amu mass defect is the nuclear energy that binds the nucleons together
• When a nucleus is formed from protons & neutrons, some mass (
) is converted to energy
2
(binding energy), related by the Einstein equation, E = mc
Fission:
•
When a heavy nucleus __________ into more __________ nuclei of smaller mass
•
Neutrons and ____________ are released
•
Occurs spontaneously and in ____________ bombs
Fission  Chain Reaction:
•
One neutron can __________ the ___________ of an atom
•
As that nucleus undergoes fission, it releases more neutrons
•
____________ released in the transmutation strike other nuclei, causing their decay and the
production of more neutrons.
•
This can cause a chain reaction
Fission:
•
If there are not enough ___________________
nuclides in the path of the ejected neutrons,
the chain reaction will _________ __________.
•
Therefore, there must be a certain minimum
amount of fissionable material present for
the chain reaction to be sustained:
_________________ __________________
Example:
0
____________________________________________________
Why is this a chain reaction?
Uncontrolled Chain Reaction?
•
This principle is used in nuclear ________________
•
Two or more masses of U-235 are contained in
bomb surrounded by powerful __________________
•
When detonated, ____________ chain reaction occurs
releasing LARGE amount of ______________ which
causes devastation to environment and life forms
•
Fortunately, concentration of U-235 in nature is
too low to start a chain reaction, most is
more stable form of ______________________
Controlled Chain Reaction:
•
Not all ________________ released in a _____________ reaction succeed in triggering
fission reaction
•
Materials that _____________ neutrons can be used to _______ chain reaction
•
Concept is used in _____________ power plants to generate ______________
Nuclear Reactors:
In nuclear reactors the __________ generated by the reaction is used to produce steam that
turns a _____________ connected to a generator.
•
The reaction is kept in check by the use of ______________
________________.
•
These block the paths of some _________, keeping the system
from reaching a dangerous _________________ mass.
•
_______________: water used to slow down fast moving neutrons
Dangers of Nuclear Radiation
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Changes structure of __________________

Changes structure of macromolecules in body – health is affected
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Particles ingested through food can damage linings of organs
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__________________ bone marrow
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Lung cancer (Radon gas)
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Genetic mutation
Beneficial Uses of Nuclear Radiation
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•
•
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_________________________–produce alpha particles to create electric current
Controlled doses are used to treat some cancers – beams of gamma rays
Radioactive tracers
Nuclear power – much less pollution, more efficient (waste must be dealt with, though)