Chapter 11 Nuclear Chemistry

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Chapter 11 Nuclear Chemistry
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Sec 11.1 Stable and Unstable Nuclides

• Nuclear chemistry deals with the concept of
  radioactivity and particles that are given off by
  radioactive substances
• The nucleus of an atom can be stable, which means
  that it does not undergo change
• If the nucleus of an atom is unstable, it will
  spontaneously undergo change

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Sec 11.1 Stable and Unstable Nuclides

• Some isotopes for an element are stable, while
  others are radioactive
• Radioactive simply means that the substance emits
  radiation (such as alpha, beta or gamma
  radiation)
• Radiation can occur when an isotope is imbalanced
  and emits a particle to become more stable

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Sec 11.2 The Nature of Radioactivity

• The field of study was pioneered by people such
  as Marie Curie in early 1900s
• The three main types of radiation are
• Alpha particles (positively charged particles)
• Beta particles (stream of electrons, neg charged)
• Gamma Rays (no particles, high energy)

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Sec 11.2 The Nature of Radioactivity

• The electromagnetic spectrum
• Note how small the spectrum of visible light
  truly is

Page 65
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Sec 11.3 Radioactive Decay

• Radioactive decay is the process by which an
  unstable nucleus emits radiation and undergoes a
  change
• One element can change into a different element
  through the process of radioactive decay

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Sec 11.3 Radioactive Decay

• Alpha
• Normally given off by heavy elements
• We write this as the following
• 238 4 234
• 92U 2He (a) 90Th
• Alpha Particles Basically a helium nucleus with
  mass 4 and charge 2

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Sec 11.3 Radioactive Decay

• Alpha Emission
• If a heavy element is unstable it may emit an
  alpha particle, which can be though of as a
  Helium Nucleus (He 4/2)
• Note that Alpha Particles have a positive charge

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Sec 11.3 Radioactive Decay

• Alpha particles transform the nucleus into
  another element with a change of mass number by 4
  and a change of atomic number by 2
• Rule of thumb, alpha radiation converts an
  element two places to the left

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Sec 11.3 Radioactive Decay

• Beta Emission
• If a nucleus has too many neutrons, it can
  convert a neutron to a proton and an electron
• We write this as the following
• 1 1 0
• 0n 1H -1e
• Beta particles e (-1) are basically electrons
  that are emitted from the nucleus

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Sec 11.3 Radioactive Decay

• Beta Particles transform the nucleus into another
  element with the same mass number but with an
  atomic number of 1
• Example P S e- (Page 67)
• Rule of thumb, beta radiation converts an element
  one place to the right

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Sec 11.3 Radioactive Decay

• Gamma
• Gamma radiation doesnt change the identity of
  the element
• We write gamma as the following
• 11 0 11
• 5B 0 g 5B
• Gamma emission Basically gamma rays are energy
  from higher state atoms to ground state atoms.
  Gamma has no mass or charge

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Sec 11.3 Radioactive Decay

• Summary of Types of Radiation

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Sec 11.4 Rate of Radioactive Decay

• Not all radioactive nuclei decay at the same
  rate, there is a large variation
• Half-life is the time it takes for one half of
  any sample to decay
• Logically, the faster the half life means that
  the nucleus is less stable

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Sec 11.4 Rate of Radioactive Decay

• It is important to realize that considering
  half-lives, a radioactive sample will never decay
  completely
• Also We do not currently know of any method to
  speed up or slow down radioactive decay
• Half-Lives can be seconds, days, or years

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Sec 11.4 Rate of Radioactive Decay
Figure 11.3 Page 271. An example of a half life
of 8 days
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Sec 11.4 Rate of Radioactive Decay
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Sec 11.5 Bombardment Reactions

• There are two main ways that a radioactive decay
  reaction takes place
• Transmutation reactions, the type discussed in
  the previous section, describes a natural and
  spontaneous radioactive decay
• Bombardment reactions are brought about by
  bombarding a stable nucleus with small particles,
  which then leads to radioactivity

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Sec 11.5 Bombardment Reactions

• Bombardment reactions were and still are used to
  discover the synthetic elements on the periodic
  table
• All the elements beyond uranium are radioactive
  and were produced through this type of experiment
• Many of the elements have a short half-life time,
  which makes them difficult to characterize, much
  less use

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Sec 11.5 Bombardment Reactions
Table 11.2 Page 274
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Sec 11.6 Radioactive Decay Series

• In many cases, a radioactive substance with a
  high atomic number (the elements starting with
  uranium and beyond) undergo a series of
  radioactive decay steps to ultimately end with a
  stable form
• Uraniun-238 for example, undergoes 14 steps
  including both alpha and beta emissions, to
  finally end up as Lead-206

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Sec 11.7 Chemical Effects

• In general, electrons of molecules are effected
  by radiation
• One, the electrons can be excited to a higher
  energy state
• Or two, the electrons can be ionized to actually
  make them leave the atom or molecule entirely
• Examples of radiation capable of causing
  ionization are X rays and Ultraviolet light

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Sec 11.7 Chemical Effects

• The radiation can strike the atom and cause
  ionization leading to an ion pair
• Fig 11.7
• Page 277

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Sec 11.7 Chemical Effects

• Usually the ion pair formation is accompanied by
  the formation of a free radical
• A free radical is a molecule or ion that has an
  unpaired electron, note that this is not common
  with normal molecules
• Free radicals are dangerous and pose problems to
  cellular activity

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Sec 11.8 Biochemical Effects

• The three main types of radioactive particles
  (alpha, beta, gamma) have different amounts of
  penetrating power
• An alpha particle is slow and normally do not
  penetrate the skin (ie stopped by a sheet of
  paper)
• The primary danger from alpha particles arises
  from ingesting a substance that emits alpha
  particles

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Sec 11.8 Biochemical Effects

• Beta particles are more penetrating than alpha
  particles and can be stopped by a thick sheet of
  aluminum
• Prolonged exposure to beta particles can cause
  harm, and once again ingesting a substance that
  emits beta radiation is harmful
• Gamma radiation is the highest penetration of the
  three types and readily passes through the skin
  into tissues and organs
• Gamma radiation can be stopped by thick lead

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Sec 11.8 Biochemical Effects
Figure 11.8 Page 279
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Sec 11.9 Detection of Radiation

• Low levels of radiation cannot be felt, tasted,
  heard, seen, or smelled
• However, there are methods to detect radiation
  levels, most famous is the Geiger Counter
• The Geiger counter is relatively portable and can
  display the levels of radiation
• Another way to detect radiation is by the use of
  photographic film that will darken when exposed

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Sec 11.10 Sources of Radiation

• Most sources of radiation are not the high energy
  dangerous sources referred to previously
• Humans are exposed to natural low level dosages
  of radiation on a daily basis from the world
  around us
• The levels of these radiation sources are much
  smaller than those generally thought to cause the
  health issues of radiation sickness

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Sec 11.10 Sources of Radiation

• Figure 11.11 Page 281

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Sec 11.11 Nuclear Medicine

• There are two main classes of uses of radiation
  in medicine
• Diagnosis
• Therapy

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Sec 11.11 Nuclear Medicine

• Diagnosis radioactive isotopes are used to
  create an image of target tissues
• Medical Imaging requires three things
• Radioactive element that goes into the tissue to
  be imaged
• Detection and mapping of the tissue to see
  concentration levels
• Computer to translate the detection map into a
  visual image

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Sec 11.11 Nuclear Medicine

• Not all radioactive materials are suitable
  choices for use in medicine
• Some criteria used are
• Detectable at low concentrations
• Short half-life to limit the time of exposure
• The radioactive material must have a known
  mechanism for elimination from the body
• The chemical properties must be mostly compatible
  with normal body biochemistry. It should be
  selective for the desired body tissue

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Sec 11.11 Nuclear Medicine

• Common choices for medical imaging

• Table 11.4 Page 284

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Sec 11.11 Nuclear Medicine

• Alternately, sometimes radioactive isotopes are
  used in therapy to selectively destroy diseased
  tissue
• The radiation kills both cancer and normal tissue
  but the cancer cells are more effected because
  they are faster dividing.
• This is why people often have hair loss or
  stomach problems, fast dividing cells

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Sec 11.11 Nuclear Medicine

• Common Choices for Therapy
• Table 11.5 Page 284

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Sec 11.12 Fission and Fusion

• Fission nuclear fission is the opposite of
  fusion and involves causing an element to
  fragment into other elements, which also can
  release energy.
• Example

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Sec 11.12 Fission and Fusion

• Fission reactions when controlled can be used to
  create atomic energy in power plants (nuclear
  power)
• Fission reactions when uncontrolled can be used
  in atomic weapons or nuclear explosions.

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Sec 11.12 Fission and Fusion

• Example of a
• Chain Reaction
• of Uranium
• Figure 11.14
• Page 285

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Sec 11.12 Fission and Fusion

• Fusion nuclear fusion is the process of smaller
  elements colliding and forming a larger element,
  which gives off a large amount of energy
• Example

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Sec 11.12 Fission and Fusion

• Fusion reactions are occurring in the sun and
  stars, giving off tremendous amounts of energy
• Fusion reactions are also responsible for the
  hydrogen bomb
• The elements that are man-made were discovered
  by controlled fusion reactions

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Sec 11.13 Comparison of Reactions

• Table 11.6 Outlines the differences between
  chemical and nuclear reactions

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Problems

• Assigned problems from pages 289 - 292
• 11.5, 11.9, 11.11, 11.15
• 11.19, 11.23, 11.26, 11.36, 11.41, 11.42
• 11.52, 11.53, 11.55, 11.63
• Practice Test page 292