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Nuclear Stability Notes
“Why do protons
stay together when
positive charges
repel each other?”
The main reason is
because of a force
called Strong Force.
Opposes the
electrostatic force.
Nuclear Stability Notes
The Strong Force is
exerted by anything
with mass (protons and
neutrons) to attract
other masses together
and works within a very
short distance.
Neutrons act as
insulation, since they
have no charge, but
have the strong force to
bring other nucleons
(protons and neutrons)
Nuclear Stability Notes
As a general rule, a
nucleus will need a
neutron/proton ratio
of 3:2 (or 1.5:1) in
order to stay
This rule is more
precise for larger
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 83.
Nuclear Stability Notes
The amount of
energy that keeps a
nucleus together is
called the Binding
This amount of
energy 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
The amount of binding energy for a
nucleus can be calculated using E =
This equation states that mass can
actually be converted into energy
(during nuclear reactions).
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 broken
Nuclear Stability Notes
If the mass that
changes is very
small, will it release
much energy?
 Energy =
(change in mass-called mass defect
x (speed of light)2
Nuclear Stability Notes
Binding Energy Calculations:
Need to know:
 speed of light = 3.00 x 108 m/s
 (speed of light)2 = 9.00 x 1016 m/s
 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
Nuclear Stability Notes
Binding Energy Calculation
#1 (Teacher example)—calculate the binding
energy of one atom of deuterium atoms
(nucleus is composed of one proton and one
neutron; measure atomic mass is 2.0140
Nuclear Stability Notes
Binding Energy Calculation
#2 (Class practice)—Calculate the binding
energy of one lithium-6 atom whose nucleus
contains three protons and three neutrons;
measured atomic mass of lithium-6 is 6.0151