Nuclear Reactions
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Transcript Nuclear Reactions
Chapter 4/25
Atomic Structure
Nuclear Chemistry
A Long, Long Time Ago…
Greek Philosophers- 4 elements are
Earth, Water, Fire, and Air
Aristotle- first recorded atomic
thoughts
Matter is continuous (no atoms)
Democritus (400 B.C.) - first recorded
atomic theory
Atoms are smallest part of matter, each type
of matter has different atoms
Aristotle and Democritus
A Long Time Ago…
Antoine Lavoisier (1782)
– Used experiments in closed containers to
develop the LCM
Joseph Proust (1799)
– Analyzed water to develop the Law of Definite
Proportions
John Dalton (1803)
– Compiled past research to develop the first
useful atomic theory
Lavoisier and Proust
John Dalton
Dalton’s theory had 4
major tenets
1.
2.
3.
4.
All matter is
composed of atoms
Atoms are indivisible
Atoms of 1 element
are alike, but different
from those of other
elements
Atoms combine in
small, whole number
ratios to form
compounds
A Reminder
Observation, Observation, Observation
Research
Hypothesis
Experiment, Revise hypothesis lots of
times
Results match….may become a theory
A Little While Ago…
1897- J.J. Thomson
discovers the
electron using a
cathode ray tube
Cathode Ray Tube
Experiment
http://www.aip.org/history/electron/jjappara.
htm
The Nucleus Exists!
1911- Ernest
Rutherford uses the
gold foil experiment
to “discover” the
nucleus
The Gold Foil Experiment
Results of Gold Foil
Experiment…
http://online.cctt.org/physicslab/content/Phy1/lesso
nnotes/atomic/atomicmodelsandspectra.asp
http://micro.magnet.fsu.edu/electromag/java/ruthe
rford/
Over 98% of the particles went straight
through
About 2% of the particles went through but
were deflected by large angles
About 0.01% of the particles bounced off the
gold foil
Rutherford’s Conclusion
Rutherford's Nuclear Model
1. The atom contains a tiny dense
center called the nucleus
– the volume is about 1/10 trillionth the volume of
the atom
2. The nucleus is essentially the entire
mass of the atom
3. The nucleus is positively charged
– the amount of positive charge of the nucleus
balances the negative charge of the electrons
4. The electrons move around in the
empty space of the atom surrounding
the nucleus
Coworker James Chadwick later adds
neutrons
Understanding Periodic
Blocks
19
K
39.0983
Atomic Number
– # of protons
Element Symbol
Mass Number
– Protons + Neutrons
Can 20.0983 Neutrons
Exist???
No, 39.0983 is an average mass of all
natural K atoms
– All K atoms MUST have 19 protons
– Some have 20 neutrons, some 19, some
21…
– Average is 20.0983 neutrons
– Individual isotopes are identified by the
number of neutrons
Identifying Protons,
Neutrons, and Electrons
Chlorine-35 (element-mass number)
# of protons = 17
# electrons = # protons
# neutrons = mass number – protons
– 35-17 = 18
Why no electrons in atomic mass?
– Electron has mass 1/1837 of Proton and
Neutron
Nuclear symbol notation (nuclide symbols)
–
–
–
–
Example: 2713Al or 27Al
# protons = ______
# neutrons = ______
# electrons = ______
Problems that arise
–
Charges and Ions: only changes the number of
–
Finding mass number: use symbol, # p+ and no,
electrons!
or periodic table IN THAT ORDER!
Atomic Mass Units
Carbon-12
– 6 protons
– 6 neutrons
1 amu = 1/12 mass of a C-12 atom
Nuclear Stability- too many
neutrons or protons causes
instability
Chemical vs. Nuclear
Change
Chemical Change- produces new kinds of
matter with new properties
– Involves breaking and forming BONDS
– Accomplished by rearrangement of
ELECTRONS
Nuclear Change- produces a new nucleus
that contains less energy
– Involves emission or capture of nuclear
particles
– Accomplished by changing PROTONS
and NEUTRONS in nucleus
Nuclear Decay
Nuclear Particles
– Alpha- rapidly moving He nuclei with a
(+) charge
– Beta – rapidly moving electrons with a (-)
charge
– Gamma – rapidly moving electromagnetic
radiation with no mass or charge
ALPHA (α)
BETA (β)
GAMMA (γ)
Symbol
4 He
2
0 e
-1
0 γ
0
Shielding
Easy
(skin/clothes)
Hard (2 cm
lead)
Energy
High
Medium
(aluminum
foil)
Med
Biological
Hazard
Actual
Hazard
High
Med
Low-Med
Low
Med
High
Low
Other Radiation
Ionizing Radiation- has significant energy
to change atoms and molecules into ions
–
–
Types: alpha, beta, gamma, x-rays
Effects to living organisms: changes in, DNA (cell
death/cancer)
Nonionizing radiation- does not have
significant energy to ionize atoms or
molecules (types: microwaves, visible
light, radiowaves)
Nuclear Reactions
–
Transmutation- Changing the nucleus of
the atom to create a new element
–
How is a Nuclear Equation Written?
Parent nuclide- initial nucleus that
undergoes changes
Daughter nuclide- nucleus resulting from
decay of parent
Types of Nuclear
Reactions
Alpha Emission- generally occurs if
nucleus has too many protons and
neutrons
Beta Emission- results from conversion of
neutron to proton and occurs if nucleus
has too many neutrons
Positron Emission- results from conversion
of proton to neutron and occurs if nucleus
has too few neutrons
Gamma Emission- often accompanies
other decay processes
Example: Alpha Decay
25299Es
______
+
4 He
2
Radioactive Decay
Half-lives
Half-life is the time taken for half of
the atoms of a radio-active
substance to decay.
Half-life
Half-lives can range
from a millionth of
a second to millions
of years
Radioactive Dating
Uses carbon-14 to tell age of fossils
C-14 is present constantly in atmosphere
15.3 decays/min in living organism
decays/min decreases by ½ every 5370
years an organism is dead.
Only useful to 60,000 yrs ago
Tracers
Radioactive isotopes used to track
pathways
Chemistry/biology- pathways of reactions
Industry and environment- path of
groundwater, durability of containers
Medicine- diagnose malfunctions
Nuclear Reactions for
Energy
Fission- nucleus
broken into 2
smaller nuclei
Fusion- smaller
nuclei join to form a
larger, more stable
nuclei
Reactants and Products
Fission- 92235U fuel
used in a chain
reaction
–
–
–
–
–
–
Limited resource
critical massminimum mass to
sustain chain reaction
Risk of runaway chain
reaction
Produces radioactive
waste products
Disposal concerns
Reaction:
Fusion- 12H and
used as fuel
1
3H
– extracted from sea
water
– not a chain reaction
– No risk of runaway
reaction
– Nonradioactive waste:
helium
– Problem: needs temp of
200 Million K
– Reaction:
Nuclear Powergenerated by
a controlled
fission chain
reaction
Control rods- absorb
neutrons to slow the
chain reaction
Made of cadmium
Inserted or
withdrawn to keep
temp of reaction
steady
Moderators- slow
neutrons down so
they DO hit uranium
fuel rods
Made of water,
beryllium, or graphite
Intended to allow
neutrons to be
absorbed by uranium
Cooling and Shielding
Water- acts as a coolant and
transfers heat between reactor and
turbines that produce electricity
Steel & concrete- surround core and
protect personnel by absorbing
radiation
Nuclear Meltdowns
Cherynobyl (Soviet
Union, 1986)
–
–
–
Runaway fission
reaction from core
meltdown
Radiation escaped to
atmosphere
31 dead, estimated
15,000 cancer deaths
in next 50 years
Three Mile Island
(Pennsylvania, 1979)
– partial meltdown
– contained before
widespread damages