Isotope Class Notes

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Isotope Class Notes
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Subatomic Particles

• Label the atom

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What are Isotopes?

• First, do you remember how to find the number of
  neutrons in an atom?
• Write the equation down in your notes

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What are Isotopes

• Isotopes are atoms that have a different number
  of neutrons.
• An atom is still the same element if it has
  different neutrons - its just a different
  version!
• Neutrons can be added to an atom without altering
  the number of protons and electrons it has.
• http//www.youtube.com/watch?vYYInVraBe7s A
  Heavy Water Experiment

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Carbon Isotopes

• For example, the element carbon has 13 different
  isotopes!
• You are familiar with C-12 (the C stands for
  carbon, and the 12 is its atomic mass)
• This isotope has 6 neutrons
• C-14 (atomic mass 14) is used for carbon dating
  and has 8 neutrons!

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More about Isotopes

• In an isotope, the number of protons and
  electrons never changes- only the number of
  neutrons is different
• This means that each isotope of a particular
  element has a different atomic mass than another
  isotope of the same element
• Remember C-12 has an atomic mass of 12 and C-14
  has an atomic mass of 14!

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Count the Number of Protons and Neutrons
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Isotope Notation

• There are several different ways to write symbols
  for isotopes, each of which is perfectly
  legitimate.

The other ways to write each of these hydrogen
isotopes from top to bottom are Hydrogen-1 or
H-1 Hydrogen-2 or H-2 Hydrogen-3 or H-3
Example Write down the three different notations
for a carbon atom with 6 protons and 6 neutrons.
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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 C-12. 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.

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Quick Activity

• Calculate the number of neutrons there are in the
  following isotopes (use your periodic table to
  find the atomic numbers)
• Carbon-14
• Nitrogen-15
• Sulfur-35
• Calcium-45
• Iodine-131

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Calculating Atomic Mass Based on Isotopes

• Most elements exist as several different
  isotopes. For example, chlorine has two
  naturally occurring isotopes
• chlorine-35
• chlorine-37
• 75.77 of the chlorine in the world exists as
  chlorine-35, and 24.23 exists as chlorine-37.

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Calculating Atomic Mass Based on Isotopes

• This is why the atomic masses on the periodic
  table are not WHOLE numbers.
• If we know how much of each isotope exists in the
  world, we can calculate the average atomic mass
  of that element (which is the number you find on
  the periodic table).

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Example

• Chlorine exists as two different isotopes,
  chlorine-35 and chlorine-37. Given that 75.77 of
  chlorine is chlorine-35 and the other 24.23 is
  chlorine-37, calculate the average atomic mass of
  chlorine.