Nuclear
Chemistry
Ch. 22
22.1 The Nucleus
• New terms:
o Nucleons- protons, neutrons and electrons
o Nuclide- the atom
• New symbols:
o 22888Ra
• Superscript = atomic mass
• Subscript= atomic #
o Radium – 228
• # is the atomic mass
Mass Defect & Nuclear
Stability
• Mass Defect- the difference between the atomic
mass & the mass of the SUM of the individual
protons, electrons and neutrons. P. 701
o How is this possible? Can’t create or destroy matter/mass or energy!
• Nuclear Binding Energy- the energy lost/released
when a nucleus is formed from nucleons.
o Think Einstein’s Theory of Relativity: E= mc2.
• Binding Energy per Nucleon- binding energy of
nucleus ÷ # of nucleons it contains.
o The higher the binding energy the more tightly held together the nucleus =
MORE STABLE NUCLEUS
Nucleons & Nuclear
Stability
• Band of Stability- the neutron-proton ratios of stable
nuclides cluster in this area. The ratios range from
1:1 to 1.5:1.
o Also, stable nuclei tend to have EVEN #s of nucleons
o “… stability of the nucleus is greatest when the nucleons- like electronsare paired”.
• Nuclear Shell model- nucleons exist in different
energy levels/shells in the nucleus.
• Magic Numbers- the # of nucleons that represent
completed nuclear energy levels: 2, 8, 20, 28, 50,
82, 126
Nuclear Reactions
• Because unstable nuclei spontaneously change (# p & # n)
in order to achieve a more stable state, they end-up
releasing large amounts of energy & particles, too.
• Nuclear Reaction- rxn that affects the nucleus of an
atom.
• Transmutation- changes in ID of a nucleus as a result of
a change in the # of protons in the nucleus.
• In any radioactive decay, the sum
of the mass #s and the atomic #s
are the same before and after the
reaction.” (on both sides of the arrow)
Try solving:
22.2 Radioactive Decay
• Radioactive Decay- spontaneous disintegration of a
nucleus into a slightly lighter nucleus, accompanied
by emission particles, electromagnetic radiation or
both.
o Nuclear Radiation- particles or electromagnetic radiation emitted from
the nucleus during radioactive decay
• Radioactive Nuclide- an unstable nucleus that
undergoes radioactive decay.
o ALL of the nuclides beyond #83 are unstable / radioactive.
Types of Radioactive
Decay
TYPE
SYMBOL CHARGE
MASS
(amu)
Alpha particle
+2
4.00260
Beta particle
-1
0.0005486
Positron
+1
0.0005486
Gamma Ray
0
0
Alpha Emission
• Alpha particle- 2 protons & 2 neutrons bound
together being emitted.
Beta Emission
• Beta particle- an electron emitted from nucleus.
o Positron emission: positron- particle that has the
same mass as an electron, but a positive charge.
Electron Capture
• - an inner orbital electron is captured by the
nucleus of its own atom.
Gamma Emission
• Gamma Rays- high-energy electromagnetic waves
from a nucleus as it changes from an excited to a
ground state.
Half-Life
• All radioactive isotopes decay at different rates.
• Half-Life- t½ , is the time required for half the atoms
of a radioactive nuclide to decay.
o More stable nuclides decay slowly. Less stable nuclides have shorter halflives and decay much more quickly.
Practice problems: Half-Life
1) If the half-life of 14056Ba is 12.75 days, how many atoms
of 14056Ba will be left after 9 weeks if there were initially 2.4
mol of atoms?
2) How long will it take 3.8 x 1024 atoms of 10047Ag to
disintegrate to 2.93 x 1023 atoms if the half life of 10047Ag is
24.6 seconds?
3) Radioactive copper, 6429Cu, is found in quantities
exceeding pollution standards in the sediments of a
reservoir in a routine check on Monday. The standard
allows up to 14 ppm/cubic meter of sediment. On Monday,
59ppm/cubic meter were measured. The half life of 6429Cu is
12.7 hours. When will the pollution level return to 14ppm?
4) An unidentified corpse was discovered on 21 April at 7:00
AM. The pathologist discovered that there were 1.24 x 1037
atoms of 3215P remaining in the victim's bones and placed
time of death sometime on 15 March. The half life of 3215P is
14.28 days. How much 3215P was present in the bones at the
time of death?
Decay Series
• - a series of
radioactive nuclides
produced by
successive decay until
a stable nuclide is
reached.
o Parent nuclide- the
initial/heaviest nuclide
that begins the decay.
o Daughter nuclide- nuclide
produced by the parent’s
decay.
Artificial Transmutation
• Artificial Radioactive Nuclides- not found naturally
on earth. MAN MADE
• Artificial Transmutation- bombardment of stable
nuclei with charged and uncharged particles.
o Results in new, heavier and unstable nucleus.
22.3 Nuclear Radiation
• Penetration Range
Radiation Exposure
• Measuring radiation:
o Roentgen- Unit used to measure nuclear radiation. The rem
(roentgen equivalent for man) – measures amount of radiation &
the sensitivity of the body
• < 150 rem: not fatal but can cause serious damage
• 150 – 1000 rem: Damaging and can be fatal
• > 1000 rem: FATAL!
Maximum permissible dose= 0.5 rem/year
Radiation Detection
Film Badge
• A small badge or pen warn on the
person.
• Like a mini Geiger counter.
• Used to monitor personal
radiation exposure.
• The film is developed after use,
the darker the film the more
exposure experienced.
Geiger- Müller counter
• Used for detecting radiation.
– As radiation passes through it’s
window, it ionizes gas in the
cylinder. Ions strike a charged
cylinder and wire which created
an electric pulse…. Which clicks
and is read on the counter.
Radiation Detection, cont.
• Scintillation counters- instruments that convert
scintillating light into electric signal for detecting
radiation.
Applications of Nuclear
Radiation
1. Radioactive Dating: process for
approximating the age of an
object based on the amount of
certain radioactive nuclides
present.
http://youtu.be/phZeE7Att_s
Applications of Nuclear
Radiation, cont.
1. .
2. Radioactive nuclides in medicine
Radiotracers: used to follow a specific substance as
it moves through a natural system. Ex- your body.
http://youtu.be/QvXHvDCesqg
http://youtu.be/7mSR--zJGv0
Applications of Nuclear
Radiation, cont.
3. Radioactive nuclides in agriculture:
• Tracers in fertilizers to test effectiveness (can see
how much was absorbed by plant).
• Food Preservation: can prevent spoiling of food and
prolong shelf life of food (for long distance
shipping).
Nuclear Waste
• The products of nuclear
fission and fusion. (P.S. fission
produces more waste than fusion.)
• Containment: 2 options.
1. On-site storage
2. Off-site disposal
• Storage: 2 stages.
1. In a pool of water
1. Then moved to a dry cask
2. Permanent underground storage
facility.
• Disposal- Needs to be long
term. Yucca Mountain
was the plan.
Nuclear Waste
22.4 Nuclear Fission &
Nuclear Fusion
Harnessing the Nucleus:
Fission vs. Fusion
Nuclear Fission
o When a heavy
element splits to
form a more-stable
nuclei of
intermediate mass.
Nuclear Fusion
o When light-mass
nuclei combine to
form a heavier, more
stable nucleus.
Nuclear Fission
• Enrico Fermi bombarded uranium238 with neutron (s) which
eventually becomes Neptunium239 (a heavier element).
• 1938 Otto Hahn & Fritz Strassman
o Tried to replicate Fermi’s experiment but
they also got Barium (a lighter element).
o Couldn’t figure out why. Wrote letter to
Meitner.
• Lise Meitner
o Thought that the nucleus must become
unstable and BREAK APART to form the
lighter atom.
Nuclear fission cont.
• Meitner was RIGHT! but Hahn got
the Nobel prize.
• Nuclear Fission- a large
nucleus is split into 2 smaller
nuclei of approximately equal
mass.
Nuclear Chain Reactions
• Because, in a fission rxn, neutrons
are released as the U atom breaks
apart, they can go and bombard
other U atoms and cause them to
break apart.
• Chain Reaction- a continuous
series of fission rxns.
o Critical Mass- the minimum amount of
nuclide that provides the # of neutrons
needed to sustain a chain rxn.
o Nuclear Reactors- use controlled-fission chain
reactions to produce energy or radioactive
nuclides.
http://youtu.be/XIvHd76EdQ4
Nuclear Power Plants
• Nuclear Power Plants- use heat from nuclear reactors to
produce energy.
• Shielding – radiation-absorbing material that is used to
decrease exposure to radiation from reactors.
• Control rods- neutron-absorbing rods that help control the
reaction by limiting the # of free neutrons.
The ATOMIC Bomb
•
•
•
•
The atomic bomb relies on a runaway chain rxn.
http://youtu.be/E-Ks-Bs0MPM
http://youtu.be/thPfjOt5WEo
http://youtu.be/RqyBzXYZPoM
Nuclear Fusion
• Nuclear Fusion- 2 small nuclei join
to form a large nucleus.
o Releases a considerable amount of
energy.
• Down side- difficult to produce and
hard to control!
Type of nuclear rxn that takes place on
the sun.
http://youtu.be/gLKykmSNbxU