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Should the existence of nuclear
waste restrain us in our
development of nuclear energy?
Nuclear Chemistry Notes
11/3 & 11/4
E=mc2
Nuclear Fission
Nuclear Stability
Radioactivity Around Us
Radioactive Decay
Half Life
Scale Model of the Atom
Atoms are mostly empty space
The
diameter
of the
atom is
100,000
times that
of its
nucleus
25 km
The emptiness of the atom is key
to understanding the relationship
of the atom to its nucleus
Which system gives the atom
its size?
Which system gives the atom
its mass?
• In most cases, regard
the two systems as
– Separate
– Independent
• Mass of a proton or a
neutron is about 2000 x
the mass of an electron
The emptiness of the atom is key
to understanding the relationship
of the atom to its nucleus
Which do you think requires less
energy to remove from the atom? A
particle of the nucleus, or an
electron? Why do you think that?
• Particles in the nucleus
are tightly locked in
• The energies available
in the nucleus are much
greater than those
available among the
electrons
The enormous energy we can get
from the nucleus follows from the
equivalence of mass and energy
Einstein’s formula tells us that a
given amountSpeed
of mass
can
be
of light is a very big number!
converted into
amount of
8 m/sec
3 xa
10specific
energy in any form, and vice versa.
http://www.seanpaune.com/wp-content/uploads/2011/03/Fukushimanuclear-power-plant.gif
Empty Space, Explosive Energy!
A nuclear
reactor can
transform fully
20% of the
mass of a
proton into
energy in each
reaction
E=mc2
Nuclear Fission
Nuclear Stability
Radioactivity Around Us
Radioactive Decay
Half Life
Chart of the Isotopes
Number Protons vs. Number Neutrons
Green dot = stable
Yellow dot = unstable
Chart of the Isotopes
#protons vs. #neutrons
 Where are the green dots when
#P about the same as #N?
– Lighter elements (atomic #<20) are
stable when #P and #N are about
equal
Green dot = stable
Yellow dot = unstable
• What happens to the ratio P:N as
the atomic # increases?
– Atom needs MORE N than P to
maintain stability
– ALL elements with atomic # >83 are
unstable (radioactive)
Nuclear Chemistry
Radioactivity
• Spontaneous release of
energy from an
unstable nucleus
Radiation
• Energy released when
an unstable atom
spontaneously decays
Types of Radiation – alpha decay
• Heavy, positively charged
particles
• a stream of helium atoms that
have no electrons
• Symbols:
An unstable nucleus
ejects a particle made
up of 2 protons and 2
neutrons
Types of Radiation – beta decay
• Light weight, negatively
charged particles
• a high energy stream of
electrons
• Symbols:
A neutron splits into a
proton, an electron,
and an antineutrino
Types of Radiation - gamma
• Pure electromagnetic
energy
• *Does not change the
element!
• Has no mass or charge
• Symbol:
Balanced Nuclear Equations
• Mass and charge must
be the same on both
sides
• We’ll do the first four
together
• You will have 8-10
minutes to work the last
6 at your table
Nuclear Decay
Do: Complete #4 through 10
Put: Write answers on the worksheet
Finish By: 5 min. total
When Done: Wait quietly until the timer rings
Be prepared to share at the document camera
How is the process of half-life
related to radioactive decay?
Half-life…
•The amount of time
required for ½ of a
radioactive substance to
decay away
Decay Series of U-238
• Has a long half-life—
4.5 x 109 years
• Decays through a series
of unstable isotopes
• Radon (Rn) gas is one of
the intermediate decay
products
Half-life of Radioactive Isotopes
• Calculate how
many half-lives
have transpired?
• Plug and chug
Half Life
Do: Complete #3 through 6
Put: Write answers on the worksheet
Finish By: 10 min. total
When Done: Wait quietly until the timer rings
Be prepared to share at the document camera
Nuclear Fission
• Fission is the splitting of a
large, unstable atom into 2
or more smaller atoms
[see p. 888 Fig.25.11]
• Fission is the process found
in atomic bombs and
nuclear reactors
Fusion Reactions
http://en.wikipedia.org/wiki/Nuclear_fusion
• Two or more smaller
atoms are combined into
a larger atom [See page
891—Fig. 25.14]
• Stars produce energy
through fusion
The Sun is a main-sequence star, and thus
generates its energy by nuclear fusion
ofhydrogen nuclei into helium. In its core,
the Sun fuses 620 million metric tons of
hydrogen each second.
E=mc2
Nuclear Fission
Nuclear Stability
Radioactivity Around Us
Radioactive Decay
Half Life
Murkiest Point Card
Do: What questions do you still have about
radioactivity and the unstable nucleus?
Put: Write your name—Period # and write 1 or 2 of
the most pressing question(s) on a notecard (on
front bench)
Finish By: Remainder of class period
When Done: turn it into the basket; if there is more
than 5 minutes of class time remaining, work on
chemistry or discuss chemistry at your table