Atomic Energy from Atoms
How are scientists able to obtain energy from splitting an atom?
The energy really comes from splitting the nucleus of an atom into two
lighter nuclei. The heaviest nuclei, like uranium 235 are not so tightly
bound since they have many positively charged protons (92 for uranium) which
repel each other. The products of the fission include two nuclei, each with
about half as many protons which are therefore more tightly bound.
In a fission reaction, the products of the fission have a total of about
0.5% less mass that the parent nucleus.
Using E = mc^2, this means that some mass has been changed to some other
form of energy.
0.5% may seem like not much, but it is about 1,000,000 times larger than the
mass reduction in a chemical reaction.
Best, Dick Plano, Professor of Physics emeritus, Rutgers University
Thanks for your question! As you probably know, atoms are very small -- and
they are very strange also. One of the strange things about atoms is that
all of the particles with positive charges (the "protons") are all very
close to each other in the central part of the atom called the "nucleus".
This is strange because the the protons have the same charge (they are all
positive) and like charges do NOT attract each other -- in fact, they
repel! If you have ever experimented with magnets, you know that like poles
(north and north, for example) repel each other and opposite poles (like
north and south) attract each other. In a similar manner, two protons will
repel each other, while an electron (which has a negative charge) and a
proton will attract each other.
So it is very strange that all the positive parts (the protons) are all
together in the nucleus of an atom. It takes a special nuclear force,
called the "strong force" to keep all of these positive charges close to
each other. Sometimes, when a neutral particle (meaning it has no charge --
it is not positive or negative), called a "neutron", enters the nucleus of
the atom the atom splits (or "fissions") into two smaller nuclei and a
couple of neutrons. These smaller nuclei require a smaller amount of energy
("binding energy") to hold them together, so some energy is released also.
The extra energy is released when the atom fissions in the form of heat.
The total amount of energy from one fission is pretty small. But if the
other neutrons also enter nearby nuclei, you can get a chain reaction that
causes a rapid, exponential increase in the amount of energy being
released. Imagine dominoes lined up. If the first domino knocks down 2
others, then those 2 knock down 4, then those 4 knock down 8, you can see
how this would grow to a very large number of dominoes falling down in a
short period of time.
If the reaction continues uncontrolled, you get the explosive energy
associated with nuclear weapons. If the reaction is controlled, you can
remove heat from the reaction with a coolant (such as water) and use the
heated water for things like generating electricity or driving an aircraft
carrier through the ocean.
For more information about how this works in nuclear power plants, see this
A heavy atom has more mass than all of the pieces after being split.
Until Albert Einstein's work with relativity, scientists believed that
mass always stays the same. If you break a ten pound block into two
pieces, you still have ten pounds of material. Splitting an atom
reduces mass. It would be like having only nine pounds of material
after splitting the ten pound block. The mass becomes usable energy
according to Einstein's E=mc^2 relationship.
At the level of individual atoms, mass acts like a form of energy. Mass
energy can change into other kinds of energy. Two common forms are heat
and light. Burning something actually uses this same principle, but on
a larger scale. Carbon has a mass. Oxygen has a mass. A carbon
dioxide molecule has a slightly smaller mass than a carbon atom and two
oxygen atoms. The slight decrease in mass becomes heat energy. This is
not nearly as powerful as splitting an atom, but it is based on E=mc^2.
Dr. Ken Mellendorf
Illinois Central College
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Update: June 2012