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Atomic Radius: Data Collection
The diagram below compares the sizes of different atoms and ions. The number represents the radius of
each atom/ ion in nanometers.
PART ONE
1. Refresher—How many nanometers = 1 meter? ________________________________________
2. Observe. These elements are arranged like they are on the periodic table. What trend (pattern)
do you notice when observing the sizes of elements within one group (vertical column)?
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3. Draw. Draw Bohr models of the elements in the first group (Li, Na, K, Rb), using the space
below. (The Bohr model of Rb is given, because it’s too big for the 2 8 8 rule.)
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4. Analyze your Bohr Models. Which of the 4 elements has the most electrons? _______________
Which of the 4 elements has the most energy levels? _________________________________
5. Interpret. Given the trend in size that you observed in #2, and the trend in energy levels that
you observed in #4, how might the number of energy levels affect the size of an atom? Explain.
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PART TWO
6. Observe. These elements are arranged like they are on the periodic table. What trend do you
notice when observing the sizes of elements within one period (horizontal row)?
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7. Draw Bohr Models for Lithium (Li) and Beryllium (Be), which are in the same period. Use the
space below.
8. Analyze your Bohr Models. A) How many energy levels does Lithium occupy (have)? ________
B) How many energy levels does Beryllium occupy? ___________
C) If the elements have the same number of energy levels, do you think the number of electrons
causes their difference in size? Explain why or why not.
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D) How many protons does Li have? _______ How many protons does Be have? ______
E) Remember that opposites attract. If 2 elements occupy the same number of energy levels,
why do you think the one with more protons is smaller?
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PART THREE
9. Refresher. Are the ions in the diagram POSITIVELY CHARGED or NEGATIVELY CHARGED? (circle
one) This means that they are examples of CATIONS or ANIONS (circle one).
10. Observe. What trend do you notice when you compare the size of each atom to the size of its
cation?
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11. Recall. How do atoms become cations? How do they get their positive charge?
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12. Analyze. Why do you think that cations tend to be smaller than their respective neutral atoms?
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PUTTING THE PIECES TOGETHER
13. Visualize. Draw ONE arrow on the diagram that describes both vertical and horizontal trends in
atomic size. Place the arrowhead near the largest atoms.
14. Challenge Problem! On Excel, create a graph that illustrates atomic radius vs atomic number
(for all elements in the diagram). Print your graph and attach it to this packet. What looks
interesting about your graph? Why do you think it shows such dramatic peaks?
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