Isotopes

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Isotopes
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Isotopes

• Remembering back to Dalton's atomic theory
• He stated that all atoms of the same element are
  identical.
• That is not true.
• The nuclei of atoms must contain the same number
  of protons in order to maintain the elements
  characteristics.

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Isotopes

• However, the number of neutrons may vary.
• Atoms that have the same number of protons but
  different numbers of neutrons are called
  isotopes.

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Atomic Mass

• The atomic mass of an element is the weighted
  average of the masses of the isotopes of that
  element.
• The atomic mass reflects both the mass and
  relative abundance of the isotopes as they are
  found in nature.

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Atomic Mass

• Example Carbon has 2 naturally occurring
  isotopes. Carbon-12 and 13. Ina sample of carbon
  98.89 of the carbon is Carbon-12 and 1.11 is
  Carbon-13. To calculate the average atomic mass
  of carbon both isotopes must be taken into
  account.
• Average(Atomic Mass A)( of A) (Atomic Mass of
  B)( of B)
• (12u)(.9889) (13u)(0.0111)
• 11.87u.144u
• 12.01u

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Applications of Isotopes

• Carbon dating
• Carbon-14 is created by the bombardment of the
  atmosphere by cosmic rays.It is an unstable
  radioactive isotope of C12. After creation it
  finds its way into living organisms. When an
  organism dies no more C-14 is added and what C-14
  is present continues to decay. To date artifacts
  scientists compare the number of C-14 atoms to
  the more common C-12 atoms in the artifact. This
  ratio along with the half-life of radioactive
  C-14 allows dating to occur.

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Applications of Isotopes

• Structural determination of compounds
• Isotopes are used to trace the formation of
  structures by acting as labels.
• Medical Uses
• Isotopes are used for diagnosis in medicine.
• Sodium-24 used to trace blood flow in the body so
  that obstructions can be detected.
• Iodine-131 has been used to test the activity of
  the thyroid gland

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Chemistry in the Environment

• The processing of uranium ore for nuclear fuel
  produces large amounts of radioactive mill
  tailings. Until the late 1970s disposal of the
  radioactive tailings was not controlled. As a
  result , millions of tons of these radioactive
  tailings are present in unmarked sites across the
  United States and Canada.