Nuclear Chemistry

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CHAPTER 25

• Nuclear Chemistry

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Radioactivity

• Marie and Pierre Curie
• Studied uranium salts
• Found that uranium emitted rays of particles even
  without the addition of outside energy
• Coined the term, RADIOACTIVITY

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Pierre Marie Curie
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Radioactivity

• The process by which the nucleus of an atom emits
  particles and rays.

Radiation
The rays and particles emitted by a radioactive
source.
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Nuclear Reactions

• Involve the nucleus of unstable atoms
• This means neutrons and protons are involved!
• Unstable atoms are called radioisotopes
• The changes in the nuclei of radioisotopes are
  accompanied by large amounts of energy.
• Cannot be slowed down or sped up by outside
  factors!

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The stability of an atom depends on its
neutron-to-proton ratio!
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• Atom Builder

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Nuclear reactions are different from chemical
reactions!
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Chemical Reactions

• Atoms gain stability by adding, losing, or
  sharing electrons
• Affected by temperature, pressure, or the
  presence of catalysts.

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How do nuclear reactions differ from chemical
reactions?
Characteristic Chemical Reaction Nuclear Reaction
Involves Nuclei
Involves Electrons
Rate can be changed
Emits energy
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How did Marie Pierres discovery affect
Daltons findings?

• They disproved Daltons Theory by saying that
  atoms are NOT indivisible.
• Particles from a radioisotope are separated from
  the nucleus during radioactive decay.

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Lets Review!

• The process by which unstable atoms give off rays
  of particles is called
• Radioactivity!

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What is the term for rays and particles given off
by a radioactive source?

• Radiation

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Whats another word for an unstable isotope?

• Radioisotope

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Name three differences between a chemical
reaction and a nuclear reaction

• 1.
• 2.
• 3.

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• Radiation is emitted during
• radioactive decay

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There are 3 types of radiation

• Alpha Radiation
• Beta Radiation
• Gamma Radiation

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Alpha Radiation

• Unstable nucleus emits a Helium atom
• 2 protons and 2 neutrons
• The mass number of the
• original atom decreases by 4
• The atomic number of the original atom decreases
  by 2

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An example of alpha radiation

• The symbol for helium is
• He (2 protons 2 neutrons)
• U Th He

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alpha radioactivity corresponds to the emission
of a helium nucleus, a particularly stable
structure consisting of two protons and two
neutrons, called an a particle.
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The Band of Stability
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Facts about alpha particles

• They are the nuclei of helium atoms
• They have two protons, so they have a postitive
  charge
• They can be sheilded by paper and clothing
• They are harmful if ingested

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Beta Radiation

• The weak nuclear force is overcome and nuclear
  particles begin to break.
• If a neutron breaks apart electron and a
  proton.
• These are the symbols you need to know
• Electron e Proton H
• Neutron n

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Beta Radiation Continued

• When the neutron breaks, the proton stays in the
  nucleus
• The electron, which is fast moving, is released
  from the atom
• Heres what happens
• n H e

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When there are too many neutrons, the atom
becomes stable by splitting a neutron.
How does this change the atomic number of the
original atom?
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A little more on Beta radiation

• Look what happens to carbon-14
• C N e
• When a neutron in carbon splits, a proton is
  gained, changing carbons atomic to 7which
  means its not Carbon, anymore! Its changed to
  Nitrogen.
• The left-over electron is released from the atom!
• This happens when there are too many neutrons!

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Positrons (still a part of Beta radiation)

• A positron occurs when a proton is converted into
  a neutron.
• This occurs when the nucleus of a radioisotope
  has too many protons for the number of neutrons!
• Cl S

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So when there are too many protons, a proton
splits and a positron is emitted.
What does losing a proton do to the atomic of
the original atom?
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Facts about Beta particles

• They have less charge than alpha particles.
• They have less mass, so theyre more penetrating.
  
• They can pass through paper but can be stopped by
  aluminum foil or wood.
• They can be electrons (ß-) or positrons (ß)

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A proton changed into a neutron, beta
radioactivity, characterized by the emission of
positron.
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The Band of Stability
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Transformation of a neutron into a proton, beta-
radioactivity, characterized by the emission of
an electron.
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The Band of Stability
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Gamma Radiation

• Gamma rays are high-energy photons
• They are electromagnetic
• Have no mass
• Have no charge
• Are extremely penetrating harmful
• Can be stopped by several meters of concrete or
  centimeters of lead

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Gamma Rays contd.

• Nuclei often emit alpha or beta particles along
  with gamma rays
• Th Ra He ?

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gamma radioactivity is not related to a
transmutation of the nucleus. It results in the
emission, by the nucleus, of an electromagnetic
radiation, like visible light or X-rays, but more
energetic. gamma radioactivity can occur by
itself or together with alpha or beta
radioactivity.