Nuclear Chemistry

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Nuclear Chemistry
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What Is Radioactivity?

• Radioactivity - The process by which atoms
  spontaneously emit high energy particles or rays
  from their nucleus.
• First observed by Henri Becquerel in 1896.

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Review

• Atoms are neutral protons electrons
• Isotopes atoms with same number of protons but
  different number of neutrons

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Nuclear Reactions v. Chemical Reactions

• Chemical reactions involve breaking of bonds in
  the reactant molecules and forming new bonds in
  the product molecules
• a. same atoms, differently arranged
• b. Conservation of mass
• c. Energy changes between 100 - 1000 kJ/mole
• Nuclear Reactions involve changes in the nucleus
• a. the atom changes into another atom
• b. a very small amount of mass is converted into
  energy. (1000 - 100,000 x chemical reactions)

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Nuclear Transmutations

• In 1902 Rutherford proposed that radioactive
  emissions result in the change of one element
  into another
• This idea was initially met with ridicule and
  disbelief as it sounded like a resurrection of
  alchemy
• But it turned out to be TRUE!
• Element 104 (Rf) Rutherfordium !

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• Nuclear Chemistry deals with only the nucleus.
• nuclide nucleus with specified number of
  protons and neutrons
• radioactivity spontaneous emission of radiation
• radionuclide radioactive nuclide
• radioisotopes atoms containing radioactive
  nuclei
• radioactive decay spontaneous decomposition to
  form a different, more stable, nucleus with the
  production of one or more particles
• decay series multiple decay steps through which
  radioactive nuclides go to reach a stable state

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Radioactive elements
He
H
Ne
F
O
N
C
Li
Be
B
Ar
Cl
S
P
Na
Mg
Al
Si
Kr
Br
Se
K
Ca
Zn
Cu
Ti
Sc
Ni
Co
Fe
Mn
Cr
V
Ga
Ge
As
I
Xe
Rb
Sr
Cd
Ag
Zr
Y
Pd
Rh
Ru
Tc
Mo
Nb
In
Sb
Sn
Te
Rn
Cs
Tl
Hg
Au
Hf
Lu
Ba
Pt
Ir
Os
Re
W
Ta
Po
Bi
Pb
At
Fr
Lr
Ra
Rf
Db
Sg
Bh
Hs
Mt
110
111
112
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The Nature of RadioactivityRutherford (1902)

-
Figure 5.1
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Penetrating Abilities of Particles
Figure 5.2
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Types of Radiation

• Alpha (?)
• Nucleus of Helium-4
• 2 charge
• Symbol or
• Beta (?)
• Composed of electrons
• 1- charge
• Symbol or
• Gamma (?)
• Electromagnetic radiation
• No charge or mass
• Unaffected by EM fields
• Highest energy form of radiation

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Gamma Rays and X-Rays

• Both gamma-rays and X-rays are forms of
  electromagnetic radiation. Gamma rays have a
  shorter wavelength and a higher energy than
  X-rays.

Figure 1.13
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Types of Radioactive Decay

• Alpha decay
• Alpha particle is released
• Example

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Types of Radioactive Decay

• Beta decay
• Three types
• Electron emission (neutron decays into an
  electron a proton)
• Example 23892U ? 0-1e 23893Np
• Positron emission (positron released)
• Example 20784 Po ? 01e 20783Bi
• Electron capture (an electron is captured by the
  nucleus)
• Example 74Be 0-1e ? 73Li

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Positrons

• Same mass as an electron, but with positive 1
  charge
• A positron is the antiparticle of an electron
• Represented by 01e

3015P ? 3014Si 01e
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Beta decay vs Positron Emission

• Beta decay occurs when a neutron is converted
  into a proton and an electron
• beta decay occurs when nuclei have too many
  neutrons
• Positron emission occurs when a proton is
  converted into a neutron plus a positron
• positron emission occurs when nuclei have too few
  neutrons

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MATTER ANTIMATTER ENERGY(according to E
mc2)
01e 0-1e ?2?
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Types of Radioactive Decay

• Gamma decay
• Results from the emission of a photon of EM
  radiation
• Nucleus of nuclide goes from an excited state to
  a ground state

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Nuclear Equations sum of both mass and atomic
numbers on both sides of equation are equal

• Examples
• 6831Ga 0-1e ? _____
• 21287Fr ? 20885As ______
• 263106Sg ? ______ 42He

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Why atoms decay

• Some nuclear arrangements are less stable than
  others.
• A radioactive isotope decays to form a more
  stable nucleus.
• It decays by emitting
• - mass (alpha particles)
• - charge (beta particles)
• - energy (gamma rays)
• There are other ways but these are not seen in
  nature.

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Radioactive Decay Series
Alpha decay
Beta decay
Lead-206 is a stable isotope
Fig 5.3
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Uses of radionuclides

• Our ability to measure radioactivity is very
  sensitive. As a result, radioisotopes have a
  number of uses.
• In addition, its interaction with living matter
  can also be exploited.
• Uses includes
• Dating techniques
• Cancer treatment
• Tracers
• Imaging
• Testing methods

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Biological damage from radiation

• breaking of chemical bonds
• DNA damage
• cell mutations
• cancer
• Formation of radicals
• Hydroxyl radicals from water
• H2O --gt H OH
• Suppress immune system
• more prone to other diseases

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Application of Radioisotopes in Medicine
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Effects of Exposure to Radiation
100 rem 1 Sv