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Transcript
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