Nuclear Chemistry

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Nuclear Chemistry

• Natural Radioactivity
• Nuclear Equations

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Nuclear Reactions vs. Normal Chemical Changes

• Nuclear reactions involve the nucleus
• The nucleus opens, and protons and neutrons are
  rearranged

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Nuclear vs. Chemical Reactions

•  
• Chemical Reaction ?
• when electron (e-) bonds are broken and formed.
• Nuclear Reaction?
• when nuclei combine, split, and emit radiation
•  
• Chemical? small change in energy, atoms retain
  identity of the element
• Nuclear? large change in energy, atoms converted
  into atoms of another element

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Discovery of Radioactivity

• Roentgen x-rays material gives invisible rays
  when bombarded with electrons.
• Becquerel minerals give off spontaneous rays

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Marie CurieClick here for her story

• Named the process by which materials
  spontaneously give off rays as RADIOACTIVITY.
• Pierre and Marie discovered Radium and Polonium

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RADIOACTIVITY

• PROCESS by which some substances spontaneously
  emit radiation
• (in form of energy or a particle).

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RADIATION

• THE ACTUAL RAYS AND PARTICLES THAT ARE EMITTED
  FROM THE NUCLEUS OF RADIOACTIVE MATERIAL.
• ? alpha
• ? beta
• ? gamma

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Elements

• Atoms are either stable or unstable
• STABLE do not give off particles or energy
• UNSTABLE constantly changing at various rates

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The isotopes of many atoms are unstable (have
extra energy). These are called radioisotopes.
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Radioisotopes emit this extra energy (radiation),
WHY DOES THIS HAPPEN ???to become more
stable, by splitting up.
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RADIOACTIVE DECAY the process of emitting
energy to gain a more stable configuration.

• SPONTANEOUS

• RANDOM

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LOSING ENERGY

• A radioisotope can lose energy by emitting three
  different types of radiation
• ALPHA
• BETA
• GAMMA

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Lets order them by size
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Alpha Particle

• a
• a helium nuclei
• 2 charge
• Low, low penetrating power (paper)
• Same as a helium-4 atom
• (He)
• 4
• 2 He or ?
• Two protons
• Two neutrons

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Beta Particle ?

• Beta
• ß-
• fast moving electrons
• charge
• blocked by metal foil
• released when a neutron turns into a proton

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Beta Particle ?

• An electron emitted from the nucleus
• 0
• e or ?
• ?1
• A neutron in the nucleus breaks down
• 1 1 0
• n H e
• 0 1
  -1

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Beta Decay neutron to proton ratio is too
GREAT

• a neutron turns into proton electron is emitted

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Beta Decay neutron to proton ratio is too
SMALL positron emissionproton turns into a
neutron and a positron is given off
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Gamma ? Radiation

• ?
• high energy electromagnetic radiation (photons)
• no net charge (0)
• Need thick block of lead or concrete to stop
• Like an X-ray but comes from the nucleus

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GAMMA RAYS

• No new atom formed when gamma rays emitted.

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Radiation Protection

• Shielding
• alpha paper, clothing
• beta lab coat, gloves
• gamma- lead, thick concrete
• Limit time exposed
• Keep distance from source

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•   Click on the picture to activate the
  animation

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Radiation Protection
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Balancing Nuclear Equations

• In the reactants and products
• Atomic numbers must balance
• and
• Mass numbers must balance

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Alpha decay
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Beta decay

• 234Th 234Pa 0e
• 90 91 ?1
• beta particle

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Gamma radiation

• No change in atomic or mass number
• 11B 11B 0 ?
• 5 5
  0
• boron atom in a
• high-energy state

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Your turn

• What radioactive isotope is produced in the
  following bombardment of boron?
• 10B 4He ? 1n
• 5 2
  0

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Solution

• What radioactive isotope is produced in the
  following bombardment of boron?
• 10B 4He 13N 1n
• 5 2 7
  0
• nitrogen
• radioisotope

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Can you write an equation from this statement?

• Write the nuclear equation for the beta emitter
  Co-60.

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Solution

• Write the nuclear equation for the
• Beta emitter Co-60.
• 60Co 60Ni 0 e
• 27 28
  -1

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Your turn - Nuclear Maddness - with a partner
find and solve 1-20 when you are done with each
card re-hide it for the next class.

• Homework is to complete the handout so if you
  finish group work early. Go ahead and start your
  homework.

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Answers to 9-14
23592U
42He 23190Th
0-1e
23190Th
23191Pa
23191Pa
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Alpha Decay, Atomic decreases by two?a helium
nucleiBeta Decay, Atomic increases by one ?
ß or e-Gamma emission, Atomic does not
change? energy (electromagnetic radiation as
photons)See page 861 in your textbook for
summary in table format.
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Electron Capture

• Electron in atoms inner shell drawn into
  nucleus and combines with proton, forms neutron
  and neutrino

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Examples

• 238U ? 234Th 4He ALPHA DECAY
• 210Bi ? 210Po ß BETA DECAY
• 11C ? 11B e POSITRON EMISSION
• ß 81Rb ? 81Kr x-rays ELECTRON CAPTURE

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Reading at home heres more information.

• Electron capture is one process that unstable
  atoms can use to become more stable. During
  electron capture, an electron in an atom's inner
  shell is drawn into the nucleus where it combines
  with a proton, forming a neutron and a neutrino.
  The neutrino is ejected from the atom's nucleus.
• Since an atom loses a proton during electron
  capture, it changes from one element to another.
  For example, after undergoing electron capture,
  an atom of carbon (with 6 protons) becomes an
  atom of boron (with 5 protons).
• Although the numbers of protons and neutrons in
  an atom's nucleus change during electron capture,
  the total number of particles (protons
  neutrons) remains the same.
• Electron capture is also called K-capture since
  the captured electron usually comes from the
  atom's K-shell.

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• In the middle range of the periodic table, those
  isotopes which are lighter than the most stable
  isotopes tend to decay by electron capture, and
  those heavier decay by negative beta decay. An
  example of this pattern is seen with silver
  isotopes, with two stable isotopes plus one of
  lower mass which decays by electron capture and
  one of heavier mass which decays by beta emission
  cobalt-57