Chapter 22
 Atomic nuclei are made of protons and neutrons which are
collectively called nucleons.
 In nuclear chemistry, an atom is referred to as a nuclide and is
identified by the number of protons and neutrons in its
nucleus.
 Nuclides can be represented two ways:
228
88Ra
• Superscript is the mass
number (total # of
nucleons)
• Subscript is the atomic
number (# of protons)
Ra-228
• Elemental symbol 1st
• Mass number follows
hyphen
Carbon, like all naturally occurring elements, has different
versions, or isotopes of itself.
Nuclide
C-12
C-13
C-14
Protons
Electrons
Neutrons
Stable?
 Stable nuclei have certain
characteristics.
 When the number of protons is
plotted against the number of
neutrons, a graph is obtained
similar to the one shown here.
 The cluster of stable nuclei that is
found in the middle of the graph is
known as the band of stability
 Among atoms having low atomic
numbers, the most stable nuclei are
those that have a neutron to proton
ratio close to 1:1
 As the atomic number increases,
the ratio increases to about 1.5:1
 Unstable nuclei will eventually undergo a spontaneous
change in their number of protons and neutrons
 In this process, they will give off large amounts of energy and
increase their stability
 These types of reactions are called nuclear reactions,
reactions which affect the nucleus of an atom
212
84Po
→
208
82Pb
+ 42He
 When the atomic number of an atom changes so does its
identity.
 A transmutation is a change in the identity of a nucleus
 Radioactive decay is the spontaneous disintegration of a
nucleus in a slightly lighter nucleus, accompanied by the
emission of particles, emr, or both.
 U-235, like Po-212, is a radioactive nuclide, an unstable
nucleus that undergoes radioactive decay.
 U-235 nucleus also becomes more stable by ejecting two
protons and 2 neutrons bound together (alpha particle)
235
92U
→ 42He + _____
 The method of decay a radioactive nuclide undergoes can be
found by using Table N of your reference tables.
 Table N gives both the decay mode and
the half-life of a number of radioactive
nuclides
 Fr-220 also undergoes α-decay
220
87Fr
→ ?
 Beta decay occurs when an unstable
nucleus ejects a β- particle
 A β- particle is a high speed electron
that is created when a neutron turns into
a proton
1
0n
→ 11p +
14
6C
→ ?
0
−1e
 Positron emission occurs when an
unstable nucleus ejects a positron
 A β+ particle is a positively charged
particle that has the same mass as an
electron
 It is created when a proton turns into a
neutron
1
1p
→ 10n +
19
10Ne
0
+1e
→ ?
 No two radioactive isotopes decay at the same rate
 Half-life, t1/2, is the amount of time required for ½ of the atoms in a
radioactive sample to undergo decay
 More stable nuclides decay at a
slower rate and have longer t1/2 s
 Less stable nuclides decay at a
faster rate and have shorter t1/2 s
 Whenever a home is bought/sold in
New York State, government
regulations state that a radon test
must be performed. If a sample of
gas taken from a basement
contains 4.38 μg of Rn-222, how
much Rn will remain in the sample
after 15.2 days?
 What percentage of an I-131
sample will remain after 40.2 days?
 One nuclear reaction is not always
enough to produce a stable nuclide.
 A decay series is a series of
radioactive nuclides produced by
successive radioactive decay until a
stable nuclide is achieved.
 The heaviest nuclide of the decay
series is called the parent nuclide.
 The nuclides produced by the
decay of the parent nuclide are
called daughter nuclides.
 Artificial radioactive nuclides are those not found naturally on
earth.
 They are made by artificial transmutations, in which nuclei are
bombarded with charged and uncharged particles
 Neutrons have no charge and thus can easily penetrate the
nucleus.
 Bombardment with positively charged particles such as protons
and alpha particles, which are repelled by the nucleus, requires
great amounts of energy
 The necessary energy may be supplied by a particle accelerator
218
84Po
→ 42He + _____
253
99Es
+ 42He → 10n + _____
142
61Pm
187
75Re
9
4Be
+ ____ →
+ ____ →
142
60Nd
188
75Re
+ 11H
+ 42He → 10n + _____
234
90Th
→
0
−1e
+ _____
Balance the following
transmutations by identifying the
missing component. Classify each
as either natural or artificial
transmutation.
 Radioactive dating is the process by which the approximate age
of an object is determined based on the amount of certain
radioactive nuclides present
 Age can be estimated by measuring either the appearance of a
daughter nuclide or the disappearance of a parent nuclide.
 The t1/2 of C-14 is 5715 years. It can be used to estimate the age
or organic material up to about 50,000 years old.
 Nuclides with longer half-lives can be used to date minerals or
rocks more than 4 billion years old
 Radioactive nuclides such as Co-60 can be used to destroy
certain types of cancer cells.
 Many radioactive nuclides can also be used as radioactive
tracers to track the movement of substances inside the body.
 I-131 can be used to diagnose thyroid disorders. The radioactive
iodine is taken up by the thyroid and a special camera captures
the radiation given off and a 3D image of the glad can be
constructed. An assessment can then be made about the shape,
size and functioning of the gland.
 Tc-99 can be used to pinpoint areas of abnormal metabolism and
identify possible cancer sites.
 In nuclear fission, a very heavy nucleus splits into more-stable
nuclei of intermediate mass.
 This process releases tremendous amounts of energy and can
occur spontaneously or when nuclei are bombarded by particles.
 When U-235 is bombarded with slow neutrons, a uranium
nucleus may capture one of the neutrons and become so
unstable that it splits instantly.
235
92U
+ 10n →
93
36Kr
+
140
56Ba
+ 3 10n
 The three neutrons produced can cause three other U-235 atoms
to fission which will produce nine neutrons…
 This process is called a chain reaction.
 A chain reaction is a reaction in which the material that starts the
reaction is also one of the products and can start another reaction.
 Nuclear power plants make use of a controlled chain reaction.
 The speed at which the reaction progresses can be controlled by
limiting both the number of free neutrons and the speed at which
they move.
 Control rods are made of neutron absorbing materials that limit the
number of free neutrons.
 A moderator is used to slow down the speed at which the neutrons
move.
 Waste that is generated from the running of a nuclear power plant
will take thousands of years to decay.
 The most common form of nuclear waste is spent fuel rods. Every
nuclear reactor in the U.S. has large pools of water where the
spent rods can be stored and some of the radioactive materials
can decay.
 When these pools are full, the spent rods are cycled out and are
moved to dry casks, which are made of high density concrete and
steel.
 Both storage means are only meant as temporary solutions before
the waste can be transported to permanent underground storage.
 The U.S. DoE has proposed a
national repository near Las
Vegas at Yucca Mountain.
 Was supposed to start taking
waste in 1998.
 Has been mired in court system
for years.
 Nuclear weapons (fission
bombs) let the chain reaction go
un-controlled.
 The material to be fissioned is
kept in two or more sub-critical
masses.
 The sub-critical masses are
brought together and the
neutrons are introduced when
detonation is desired.
Becoming a nuclear power.
 In nuclear fusion, light-mass
nuclei combine to form a
heavier, more stable nucleus.
 Nuclear fusion releases more
energy per gram of fuel than
nuclear fission.
 In the sun and other stars, four
hydrogen nuclei combine at
extremely high temperature and
pressure to form a helium
nucleus with a loss of mass and
release of energy.
H-2
H-3
He-4