Lecture Notes:
Creation of the Elements
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Natural Elements
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The elements on the periodic
table are not all naturally occurring
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All the
elements from atomic number 1 to atomic number 92
(uranium, U) are naturally occurring
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OK, element 43 (Technetium, Tc) is only found in very large stars and has not been found on earth in any concentration; elements 85 (Astatine, At) and 87 (Francium, Fr) are found in extremely small amounts on earth; people wishing to study these three elements usually do so by creating them synthetically
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All the naturally occurring elements were formed by
nuclear reaction in stars
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Nuclear fusion is a process by which atomic nuclei
are subjected to such high energy and pressure that
they fuse together to become a new element
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The process of nuclear fusion is what causes the sun
to shine
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In the sun four H nuclei combine to form one He
nucleus; the He nucleus has less mass than the four H
nuclei; the ‘missing‘ mass is the energy
that causes the sun to shine
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As you probably know, E = mc2; this means
that matter can be changed into energy and that
energy can be changed into matter
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Everything on earth is made up of elements formed in
the centers of stars that exploded before the sun was
born
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Synthetic Elements
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Elements 93-118 were
all created by scientists in the laboratory
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These elements are radioactive and rapidly decay to
become lighter elements; this is why they do not occur naturally even though they may actually form as a result of stellar nuclear reactions
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Elements can be created by the disintegration of
large nuclei into two or more smaller nuclei; this
process is called fission and occurs on a large scale
in nuclear power reactors
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Elements can also be created by bombarding atoms with
other atoms at very high speeds; they can be made to
combine to form a new isotope
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Energy and particles such as neutrons,
electrons, positrons, and hydrogen nuclei (protons)
are produced in these nuclear reactions