1. Atomic Structure ATOMS IONS ISOTOPES Differ by number of protons
Differ by number of electrons
ISOTOPES
Differ by number of neutrons
Most of the known elements have at least one isotope whose atomic nucleus is stable indefinitely
A great majority of elements also have isotopes that are unstable and disintegrate, or decay, at measurable rates by emitting radiation
Some elements have no stable isotopes and eventually decay to other elements
The process of nuclear decay is a nuclear reaction that results in changes inside the atomic nucleus Each element can be represented by the notation Z X
A is the mass number, the sum of the numbers of protons and neutrons
Z is the atomic number, the number of protons
The protons and neutrons that make up the nucleus of an atom are called nucleons
An atom with a particular number of protons and neutrons is called a nuclide
Nuclides that have the same number of protons but different numbers of neutrons are called isotopes
The number of neutrons is equal to A – Z

2. Mass Defect
Difference between the mass of an atom and the mass of its individual particles.
amu
amu
Courtesy Christy Johannesson

3. Nuclear Binding Energy
Energy released when a nucleus is formed from nucleons.
High binding energy = stable nucleus.
E = mc2
E: energy (J)
m: mass defect (kg)
c: speed of light (3.00×108 m/s)
Courtesy Christy Johannesson

4. Nuclear Binding Energy
10x108
9x108
Fe-56
He-4
U-238
8x108
7x108
B-10
Binding energy per nucleon
(kJ/mol)
6x108
5x108
Li-6
4x108
3x108
2x108
H-2
1x108 20 40 60 80
100
120
140
160
180
200
220
240
Mass number
Unstable nuclides are radioactive and undergo radioactive decay.

5. Mass Defect and Nuclear Stability
2 protons: (2 x amu) = amu
2 neutrons: (2 x amu) = amu
2 electrons: (2 x amu) = amu
Total combined mass: amu
= amu
The atomic mass of He atom is amu.
This is amu less than the combined mass.
This difference between the mass of an atom and the sum of the masses
of its protons, neurons, and electrons is called the mass defect.

6. Nuclear Binding Energy
What causes the loss in mass?
According to Einstein’s equation E = mc2
Convert mass defect to energy units
amu
x kg
1 amu
= x kg
The energy equivalent can now be calculated
Nuclear reactions are accompanied by changes in energy
Energy changes in nuclear reactions are enormous compared with those of even the most energetic chemical reactions
Energy changes in a typical nuclear reaction are so large that they result in a measurable change of mass
Nuclear reactions are accompanied by large changes in energy, which result in detectable changes in mass.
The relationship between mass, m, and energy, E, is expressed in the equation E = mc2, where c is the speed of light (2.998 x 108 m/s), and energy and mass are expressed in units of joules and kilograms, respectively.
Every mass has an associated energy, and any reaction that involves a change in energy must be accompanied by a change in mass.
Large changes in energy in nuclear reactions are reported in units of keV or MeV; a change in energy that accompanies a nuclear reaction can be calculated from the change in mass (1 amu = 931 MeV).
Chemical reactions are accompanied by changes in mass, but these changes are too small to be detected
E = m c2
E = ( x kg) (3.00 x 108 m/s)2
E = (4.54 x kg m2/s2) = 4.54 x J
This is the NUCLEAR BINDING ENERGY, the energy released
when a nucleus is formed from nucleons.

7. Binding Energy per Nucleon
mass number
(# of protons
+ neutrons)
1) Calculate mass defect 7 Li
protons: amu
neutrons: amu 3
atomic number
(# of protons)
electrons: amu
Li - 7
2) Convert amu kg
1 amu
________ amu
x kg
= _______ kg
The mass of an atom is always less than the sum of the masses of its component particles; the only exception is hydrogen-1.
The difference between the sum of the masses of the components and the measured atomic mass is called the mass defect of the nucleus.
The amount of energy released when a nucleus forms from its component nucleons is the nuclear binding energy.
The magnitude of the mass defect is proportional to the nuclear binding energy, so both values indicate the stability of the nucleus.
Not all nuclei are equally stable; the relative stability of different nuclei are described by comparing the binding energy per nucleon, which is obtained by dividing the nuclear binding energy by the mass number A of the nucleus.
The binding energy per nucleon increases rapidly with increasing atomic number until Z = 26, where it levels off and then decreases slowly.
3) E = mc2
speed of light (c) x108 m/s
4) Divide binding energy by number of nucleons

8. The Energy of Fusion
The fusion reaction releases an enormous amount of energy relative to the
mass of the nuclei that are joined in the reaction. Such an enormous amount
of energy is released because some of the mass of the original nuclei is con-
verted to energy. The amount of energy that is released by this conversion
can be calculated using Einstein's relativity equation E = mc2.
Suppose that, at some point in the future, controlled nuclear fusion becomes
possible. You are a scientist experimenting with fusion and you want to
determine the energy yield in joules produced by the fusion of one mole of
deuterium (H-2) with one mole of tritium (H-3), as shown in the following
equation:

9. amu
amu
amu
amu
amu
amu
amu
amu
First, you must calculate the mass that is "lost" in the fusion reaction. The
atomic masses of the reactants and products are as follows:
deuterium ( amu), tritium ( amu), helium-4 ( amu),
and a neutron ( amu).
Mass defect: -
amu

10. According to Einstein’s equation E = mc2
Mass defect = amu
According to Einstein’s equation E = mc2
Convert mass defect to energy units
amu
x kg
1 amu
= x kg
The energy equivalent can now be calculated
E = m c2
E = ( x kg) (3.00 x 108 m/s)2
E = (2.81 x kg m2/s2) = 2.81 x J
This is the NUCLEAR BINDING ENERGY, for the formation
of a single Helium atom from a deuterium and tritium atom.

11. Therefore, one mole of helium formed by the fusion of one mole of deuterium
and one mole of hydrogen would be 6.02 x 1023 times greater energy.
2.81 x J x
6.02 x 1023
1.69 x J of energy released per mole of helium formed
1,690,000,000,000 J
The combustion of one mole of propane (C3H8), which has a mass of 44 g,
releases x 106 J. How does this compare to the energy released by
the fusion of deuterium and tritium, which you calculated?
C3H8 + O H2O + CO x 106 J
(unbalanced)
44 g
4 g He
1,690,000,000,000 J
Fusion produces ~1,000,000 x
more energy/mole
44 g C3H8
2,043,000 J

12. Lise Meitner and Otto Hahn
Meitner, Lise Image:
AUSTRIAN PHYSICIST 1878–1968
On any list of scientists who should have won a Nobel Prize but did not, Lise Meitner's name would be near the top. She was the physicist who first realized that the atomic nucleus could be split to form pairs of other atomic nuclei—the process of nuclear fission. Although she received many honors for her work, the greatest of all was to elude her because of the unprofessional conduct of her colleague Otto Hahn.
Born in Vienna, Meitner decided early on that she had a passion for physics. At that time, education for female children in the Austro-Hungarian Empire terminated at fourteen, as it was argued that girls did not need any more education than that to become a proper wife and mother. Willing to support his daughter's aspirations, her father paid for private tutoring so she could cover in two years the eight years of education normally needed for university entrance. In 1901 Meitner was one of only four women admitted to the University of Vienna, and in 1905 she graduated with a Ph.D. in physics.
As a student, Meitner had become fascinated with the new science of radioactivity, but she realized that she would have to travel to a foreign country to pursue her dream of working in this field. She applied for work with Marie Curie, but was rejected. However, she did eventually receive an offer from the University of Berlin, which had just hired a young scientist by
Austrian physicist Lise Meitner standing with Otto Hahn (l.). Meitner discovered nuclear fission, but was never honored as such.
the name of Otto Hahn. Having a chemical background, Hahn was looking for a collaborator with a theoretical physics background. Unfortunately, the chemistry institute at the university was run by Emil Fischer who had banned women from the institute's premises. Reluctantly, Fischer agreed to let Meitner work in a small basement room. During this time, she received no salary and relied on her family for enough money to cover her living expenses. Meitner and Hahn's research during this time period resulted in the discovery of the element protactinium.
The post–World War I government in Germany was much more favorable to women, and Meitner became the first woman to serve as a physics professor in that country. By the 1930s scientists were bombarding heavy elements with neutrons and it was claimed that new superheavy elements formed as a result of this process. Using such a procedure, Meitner and Hahn thought they had discovered nine new elements. Meitner was puzzled by all the new elements for which claims were made.
Unfortunately, the Nazi Party's rise to power changed everything for Meitner. Because she was a Jew by birth, although a later convert to Christianity, Meitner's situation became increasingly precarious. With help from a Dutch scientist, Dirk Coster, she escaped across the German border into Holland and then made her way to Stockholm, where the director of the Nobel Institute for Experimental Physics reluctantly offered her a position. Stockholm had one advantage for Meitner, an overnight mail service to Germany so she could keep in regular contact with Hahn.
On December 19, 1938, Hahn sent Meitner a letter describing how one of the new elements had chemical properties strongly resembling those of barium and asking if she could provide an explanation. The physicist Otto Frisch visited Meitner, his aunt, for Christmas to help dispel her loneliness. While there, the two went for the now famous "walk in the snow." During an extended conversation in the woods, they came to realize that if the nucleus was considered a liquid drop, the impact of a subatomic particle could cause the atom to fission. If so, it was possible that the barium-like element was actually barium itself.
Meitner immediately contacted Hahn and his colleague Fritz Strassmann. Through experiment they confirmed that the so-called new element was indeed barium. They reported their discovery of nuclear fission to the world's scientific press, barely mentioning the names of Meitner and Frisch. In fact, Hahn never admitted that it was Meitner who had made the critical conceptual breakthrough. In 1944 Hahn was awarded the Nobel Prize in chemistry for his contribution to the discovery of nuclear fission.
Although nominated several times, Meitner never did receive the Nobel Prize for physics that many scientists considered her due. Only now, with element 109 having been named Meitnerium (symbol Mt) has she finally received some recognition for her crucial work. Meitner retired to England where she died at the age of eighty-nine.
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