Nuclear Chemistry

Front 1

The stability of an isotope depends on:

Back 1

The ratio of protons to neutrons in the nucleus...
-most nuclei are stable, but some are unstable. These nuclei will spontaneously decay, emitting radiation.

Front 2

Ratio of stable isotopes

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Stable isotopes have a 1:1 ratio of protons and neutrons. Most radioactive isotopes have twice as many neutrons as protons.

Front 3

Elements that are radioactive

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All elements with an atomic number higher than 83 are radioactive.

Front 4

Half life

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Each isotope has a specific mode and rate of decay. The rate of decay is called half life. The half life is a constant and can never be changed.

Front 5

What does half life measure?

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Half life is the measure of the time it takes exactly one half of an amount of isotope to decay.

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Decay to zero

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The amount of substance will NEVER decay to zero.

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Transmutation

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A change in the nucleus of an atom changes it to a new type of atom (i.e. a new element). This is called transmutation.

Front 8

How does a transmutation occur?

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Transmutation can occur naturally or artificially. Artificial transmutation requires the bombardment of a nucleus by high energy particles.

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Spontaneous decay

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Spontaneous decay can involve the release of different particles from the nulceus.

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Nuclear reactions

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Nucleaur reactions include natural and artificial decay, nuclear fission and nuclear fission

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Nuclear fission

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Nuclear fission occurs when the nucleus of an atom is split. This can be caused artifically by "shooting" the nucleus with a neutron.

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Nuclear fusion

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Nuclear fusion combines two light nuclei to form heavier nuclei Nuclear fusion is the process that powers the sun.

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What does nuclear fusion require?

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Nuclear fusion requires very high temperatures, and is not yet ready for practical use. The main advantage it offers is that the products are not radioactive wastes (as with fission).

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How can nuclear reactions be represented?

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Nuclear reactions can be represented by equations that include symbols with represent atomic nuclei (with mass number and atomic number), subatomic particles (with mass and charge) and emitted particles.

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Energy from nuclear reactions

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Energy from nuclear reactions comes from teh very small fraction of mass that is lost - the reaction converts matter into enerty.

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E=mc^2

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Einstein's E=mc^2 describes the relationship between energy and matter.

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Energy released from nuclear reactions

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The energy released from nuclear reactions is much greater than that released from chemical reactions.

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Risks with using radioactive isotopes

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Risks associated with using radioactive isotopes include biological exposure (which may cause radiation poisonig and cancer), long-term storage and disposal, and nuclear accidents.

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Uses for radioactive isotopes

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Radioactive isotopes may be used in medicine (tracing chemical and biological processes), radioactivbe dating, industrial measurement, nuclear power, and detection and treatment of disease.

Front 20

Wilhelm Roentgen

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(145-1923) discovered X-rays, a high energy form of light (1895)

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Henri Becquerel (1852-1909)

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found that uranium ores emit radiation that can pass through objects (like x-rays) and affect photographic plates (1896)

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Marie Sklodowska Curie (1867-1934)

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Marie and Pierre worked with Becquerel to understand radioactivity. The three scared a Nobel Prize in Physics in 1903. Marie won a second Nobel Prize in Chemistry in 1911 for her work with radium and its properties.

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E.O. Lawrence

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invented the cyclotron which was used at UC Berkeley to make many of the transuranium elements.

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radioactivity

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the spontaneous breakdown of atomic nuclei, accompanied by the release of some for of radiation (also called radioactive decay)

Front 25

half-life

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time required for half of the radioactive sample to decay

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transmutation

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one element being converted into another by a nuclear change

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nuclides

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isotopes of elements that are identified by the number of their protons and neutrons

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emission

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the particle ejected from the nucleus

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decay series

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the sequence of nuclides than an element changes into until it forms a stable nucleus

Front 30

radioactive dating

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using half-life information to determine the age of objects. C-14/C-12 is common.

Front 31

nuclear fission

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large nucleus breaking down into pieces of about the same mass.

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nuclear fusion

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two or more light nuclei blend to form one or more larger nuclei

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Alpha particles

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are the same as a helium nucleus, with a mass of 4amu. It travels about 1/10th the speed of light and is most easily stopped of the three particles (a sheet of paper will stop them). It is the least dangerous.

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Beta particles

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are high speed electrons, with a mass of 0.00055 amu and travels at nearly the speed of light. It can be stopped by a sheet of aluminum. It is more penetrating and therefore more dangerous than alpha.

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Gamma rays

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are extremely high energy light, with no mass, and are the most penetrating (several cm's of lead are needed to stop them). They can cause severe damage.

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Four variables of half-life problems

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total time
half-life
starting amount
ending amount

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Reasons a nucleus can be unstable

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-The nucleus has too many protons compared to neutrons
solution: positron decay
-The nucleus has too many neutrons compared to protons
solution: beta decay
-The nucleus is too big (too many protons and neutrons)
solution: alpha decay

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Positron decay

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Change a proton into a neutron and a positive electron...a positron

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Beta decay

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Change a neutron into a proton and a negative beta particle

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Alpha decay

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lose 2 p+ and 2n

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Radioactive dating

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In every living thing, there is a constant ratio of normal C-12 and radioactive C-14. You can calculate the time needed to change from what is expected to what is actually found.

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Fission reactors

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Current nuclear reactors use fission reactions to produce heat which is used to turn water into steam and drive turbine engines that produce electricity.

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Radioisotopes

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Many substances can be radioactive and then followed as they move through the body.

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The sun and stars

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The sun and the stars are powered by nuclear fission reactions to produce heat which is used to turn water into steam and drive turbine engines that produce electricity.