CHAPTER 25 Nuclear Chemistry

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CHAPTER 25 Nuclear Chemistry
I

• I. The Nucleus -Terms
• (p. 798-820)

II
III
IV
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Ionizing Radiation

• Radiation is a form of energy transferred by
  waves or atomic particles
• Ionizing Radiation is any radiation with high
  enough energy to create ions (by knocking
  electrons out of atoms)
• like UV, X, gamma, and cosmic rays
• There are both natural sources of radiation
  (unstable nuclei and stars) and human created
  sources

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Zone of Stability

• Stable nuclei exist within the zone of
  stability seen on the graphnot always a 11
  ratio of p to no
• Outside this range, nuclei are unstable and will
  decay (disintegrate) into new nuclei

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Definitions

• Nucleons particles in nucleus (p and n0)
• Nuclide refers to the nucleus of an atom
• Nuclear Reactions involve transmutation where one
  element become another.
• Radioactive Decay is the when unstable nuclei
  spontaneous lose energy by emitting ionizing
  particles as this changes the nucleus of the
  atom, this also changes the type of element

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Alpha Decay Process
Daughter Nuclide Np-237 Th-234 Ra-228 Rn-222
???????
Parent Nuclide Am-241 U-238 Th-232 Ra-226
Alpha Particle (Helium Nucleus) (4.00147 amu)
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A. Mass Defect

• The mass defect describes the mass lost during
  the formation of nuclei
• Difference between the mass of an atom and the
  mass of its individual particles.

4.00260 amu Mass of atom
4.03298 amu Mass of particles
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B. Nuclear Binding Energy

• Energy released when a nucleus is formed from
  nucleons. This contributes to the loss in mass of
  nucleus, described by E mc2.
• High binding energy stable nucleus.

E mc2
E energy (J) m mass defect (kg) c speed of
light (3.00108 m/s)
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B. Nuclear Binding Energy
Iron (Fe) is the most stable nucleus!!
Unstable nuclides are radioactive and undergo
radioactive decay.
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CHAPTER 25 Nuclear Chemistry
I

• II. Radioactive Decay
• (p. 798-820)

II
III
IV
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Types of Spontaneous Radiation
stopped by
Greek symbol
charge

• Alpha particle (?)
• helium nucleus

paper
2

• Beta particle ? or ?-
• electron

1-
wood

• Positron ?
• positron

1
Lead or concrete

• Gamma (?)
• high-energy photon

0
11
Other Radiation particles
Greek symbol
charge

• proton p

1

• neutron n0

0
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How does an electron get emitted from the nucleus?

• Basically a neutron splits into a proton which
  stays in the nucleus and an electron is emitted
  (? decay)

-


-



n converted to a proton and an e is emitted
n p in nucleus
n is really like a p and e together
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Transmutation Reactions

• I Alpha Emission

Numbers must balance on both sides of
arrow!! 238amu on left (234 4amu) 92 is nucl
chrg on left 90 2 on right
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B. Nuclear Decay

• II Beta Emission

• III Positron Emission

a proton 1p is not the same as a positron 0e
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B. Nuclear Decay

• IV Electron Capture

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B. Nuclear Decay

• V Alpha Capture followed by neutron emission

• Gamma Emission causes no change in mass or charge
  and
• Usually follows the previous
• types of decay.

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Beta (Negatron) Decay Process
Daughter Nucleus Osmium-187 Calcium-40
???
Antineutrino
Parent Nucleus Rhenium-187 Potassium-40
?????
Beta Particle (electron)
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Beta Particles

• Same as an electron with kinetic energy
• Positive or negative charge of 1
• May be positively or negatively charged
• Can normally be stopped by 1 cm of plastic, wood,
  paper
• Exception for positron emitters

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B. Nuclear Decay

• Why nuclides decaypg. 803
• need stable ratio of neutrons to protons

DECAY SERIES TRANSPARENCY
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C. Half-life

• Half-life (t½)
• Time required for half the atoms of a radioactive
  nuclide to decay.
• Shorter half-life less stable.

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C. Half-life
mf final mass mi initial mass n of half-lives
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C. Half-life

• Fluorine-21 has a half-life of 5.0 seconds. If
  you start with 25 g of fluorine-21, how many
  grams would remain after 60.0 s?

GIVEN t½ 5.0 s mi 25 g mf ? total time
60.0 s n 60.0s 5.0s 12
WORK mf mi (½)n mf (25 g)(0.5)12 mf 0.0061
g
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Decay Series

• Many heavy elements are unstable and so they will
  continue to decay (be radioactive) until they
  finally transmute into a stable nucleus.
• Here is an example of the Th-232 decay series
• Thorium oxide is used to in camping lanterns to
  intensify the brightness when on fire.

Stable isotope