1. Atoms and Isotopes the light bulb is a reminder
4/24/2017
Atoms and Isotopes
the light bulb is a reminder
you need to do something
on your notes page

2. What are isotopes? Key Why are all these atoms still called CARBON?
4/24/2017
What are isotopes?
Atoms of an element that have different masses
This occurs by changing the number of neutrons in the nucleus.
Key
AMU = atomic mass unit
Carbon-12
atomic mass = 12 AMU
6 p+ and 6 n = 12 AMU
Carbon-13
atomic mass = 13 AMU
6 p+ and 7 n = 13 AMU
Carbon-14
atomic mass = 14 AMU
6 p+ and 8 n = 14 AMU
Why are all these atoms still called CARBON?
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3. What are isotopes? Key Isotopes of Hydrogen H H H
Standard atomic
notation
Hydrogen-1
atomic mass = 1 AMU
1 p+ and 0 n = 1 AMU
AMU = atomic mass unit 1 H 1
Periodic Table Notation
Mass number on top
Hydrogen-2 (deuterium)
atomic mass = 2 AMU
1 p+ and 1 n = 2 AMU 2 H 1
Atomic number on bottom
Hydrogen-3 (tritium)
atomic mass = 3 AMU
1 p+ and 2 n = 3 AMU 3 H 1
 Hydrogen is the only element that has different names for its
isotopes
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4. Isotopes are written using standard atomic notation.
Potassium has three isotopes,
Potassium is found in nature in a certain ratio of isotopes.
93.2% is potassium-39, 1.0% is potassium-40, and 6.7% is potassium-41
Atomic mass = (0.932 x 39) + (0.001 x 40) + (0.067 x 41) = 39.1 AMU
So why is the mass of K listed as 39.1 AMU?
AMU = atomic mass unit
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5. What is Radioactivity?
Elements that are RADIOACTIVE have nuclei that is UNSTABLE.
Why is this nucleus unstable?
Count up the number of protons and neutrons – are there more attractive or repulsive forces in this nucleus?
A nucleus is unstable if it has
too many particles in the nucleus.
To become STABLE, they give up
particles or energy and this is…….
Radioactivity
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6. What is Radioactivity?
The strong nuclear force holds the protons and neutrons together but when the repulsive force of the protons gets too large then the atom undergoes radioactive decay.
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7. Radioactive Decay Parent nucleus (unstable) Daughter nucleus
Radioactivity released
The radioactivity released can be
particles or energy
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8. What is Radioactivity?
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9. Radioactivity All elements have at least one radioactive isotope.
4/24/2017
Radioactivity
All elements have at least one radioactive isotope.
All isotopes with atomic number greater than 83 are radioactive.
Graph of Stable and Unstable isotopes
Example: Uranium-238
Proton number = 92
Neutrons = 146
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10. Periodic Table
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11. Uranium 238 decay (U-238) Unstable parent nucleus First decay product
Q: Why is the mass of the daughter nucleus
less than the mass of the parent nucleus?
A: The daughter nucleus has LOST neutrons
to become stable.
Q: Why is the atomic number of the daughter
nucleus less than the atomic number of the
parent nucleus?
A: The daughter nucleus has LOST protons
to become stable and has
become a different element.
Stable daughter nucleus
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12. Uranium 238 decay The half life of U-238 is 4.5 billion years.
If you start with 100 g of U-238
4.5 billion years later you have
50 g of U-238
(half of parent left)
50 g of Pb-82
(new daughter element)
Slide 11