Transcript Nuclear Stability Notes

Nuclear Stability Notes
Nuclear Stability Notes
• The type of symbol used to
represent any atom is:
• The element symbol (found on
periodic table)
• A superscript number listed
before the symbol (represents
the atomic mass)
• A subscript number listed
before the symbol (represents
the atomic #)
Carbon-12 atom
Nuclear Stability Notes
• A nucleus is made up
of protons
(+1 charge) and
neutrons (0 charge).
• Q--Why do protons
stay together when
positive charges repel
each other?
• A--The main reason is
because of a force
called Strong Force
Nuclear Stability Notes
• Strong Force is
exerted by anything
with mass (protons
and neutrons) to
attract other masses
together.
• Strong force will only
work within a very
short distance.
Nuclear Stability Notes
• Neutrons act as
insulation, since they
have no charge to
push protons away,
but have strong force
to bring other
nucliides (protons and
neutrons) together.
Nuclear Stability Notes
• As a general rule, a
nucleus will need a
neutron/proton ratio of
3:2 (or 1.5) in order to
stay together.
• This rule is more
precise for larger
nuclei. (see page
866).
Nuclear Stability Notes
• Of all known isotopes
of natural elements
(about 1500), only
250 of them are
stable.
• All of these stable
isotopes have an
atomic number in
between 1 and 82.
Nuclear Stability Notes
• The amount of energy
that keeps a nucleus
together is called the
Binding Energy.
• This amount of
energy (per nucleon)
is higher for nuclei
that are stable than it
would be for unstable
nuclei.
• It is measured in units
called “Joules” or J.
Nuclear Stability Notes
Nuclear Stability Notes
• The amount of
binding energy for a
nucleus can be
calculated using
E = mc2.
• This equation states
that mass can
actually be converted
into energy (during
nuclear reactions).
Nuclear Stability Notes
Nuclear Stability Notes
• The mass of a
nucleus will be less
than the mass of all of
the protons and
neutrons making it up.
The difference is
called the mass
defect, which is
converted into energy
if the nucleus is
formed.
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http://www.aip.org/history/mod/fission/fission1/02.html
http://www.aip.org/history/einstein/emc1.htm#ae22
http://www.aip.org/history/einstein/voice1.htm
• If the mass that
changes is very small,
will it release much
energy?
Nuclear Stability Notes
• Energy =
(change in mass-called mass defect)
x (speed of light)2
• See example on page
617.
Nuclear Stability Notes
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need to know:
speed of light = 3.00 x 108 m/s
(speed of light)2 = 9.00 x 1016 m2/s2
conversion factor for amu to kg = 1.66054
x 10-27 kg/amu
• mass of H atom (close to mass of proton)=
1.007825 amu
• mass of neutron = 1.008665 amu