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## Homework: The Table of Isotopes

### Directions

Answer questions using complete sentences. For calculations, show work and show units. Use the correct number of significant figures, where appropriate. ##### Questions
Refer to the graph at left to answer the following questions. This graph should look familiar from what we have covered in class: it has to do with the stability of the isotopes.
1. What is the label for the x-axis in this graph?
2. What is the label for the y-axis in this graph?
1. What does the line on the graph that starts at (0, 0) mean?
2. Why is it important?
1. What do the blacked-in squares on the graph represent?
2. Why are they clustered toward the middle of the group of squares on the graph?
1. What do the open squares on the graph represent?
2. Why are they toward the edges of the group of squares on the graph?
1. Why are there no squares in the area marked with ‘6’?
2. Why are there no squares in the area marked with ‘7’?
3. What do the squares with a dot in them mean (marked 8 in the key)?

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1. What two forces are important when it comes to an isotope being stable or unstable?
2. What role does the electrostatic force play in determining the structure of the graph on the previous page?
3. What role does the strong nuclear force play in determining the structure of the graph?
4. What forces have to be balanced to make an isotope stable? Draw a picture to illustrate the difference between a stable and an unstable nucleus.
The dark grey isotopes are stable. Unmarked isotopes are unstable. 1. Make a graph on graph paper: record the number of protons and neutrons for each isotope in the chart at right as a square of the graph. Shade the stable isotopes by filling in those squares. Draw a line on this graph for the places
where p+ = n0.
2. Do any stable isotopes lie on the line where p+ = n0? Why or why not?
3. What is the ratio of n0 to p+ for stable isotopes in this part of the table of isotopes? (Come up with a way to figure this out.) Compare it to the ratio for isotopes near Z = 6 and to isotopes near Z = 80. Put them in order and explain why each one has the value that it has. Use what you know about what makes a nucleus stable/unstable.

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1. What happens to an isotope that is radioactive?
2. What particle in the nucleus causes isotopes to the right and below the zone of stability to be radioactive? Think about the n0/p+ ratio in that area.
3. What particle in the nucleus causes isotopes to the left and above the zone of stability to be radioactive? Think about the n0/p+ ratio in that area.
4. Define the following terms
carefully and completely
1. nucleon:
2. atom:
3. atomic number:
4. atomic mass number:
5. stable isotope: