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Discovering a Periodic Trend

Last updated over 4 years ago
6 questions
Atomic radius is the distance between the center of the nucleus and the outer orbital of the atom. We know that atomic radius increases as you move down a row on the periodic table because you have an additional orbital each time you move down. As you move across a period on the periodic table, you find that the number of protons, neutrons, and electrons increases, but the number of energy levels remains the same.
2

Write a hypothesis to tell what you think happens to the atomic radius as you move across a period. Use this template to form your answer, "If you move from left to right across a period,then the atomic radius will...because..."

8

The elements below are all from the same period and have the same number of energy levels. The name of the element is followed by its atomic radius. Put them in order by the Zeff for their valence electrons so that the one with Zeff of 1 is first, then 2, then 3, etc. Remember that elements in column 1 have a Zeff of 1 and elements in column 2 have a Zeff of 2, etc.

  1. aluminum 143 pm
  2. Sodium 186 pm
  3. silicon 118 pm
  4. magnesium 160 pm
  5. argon 97 pm
  6. chlorine 99 pm
  7. Phosphorus 110 pm
  8. sulfur 103 pm
5

Make a graph that shows Zeff of each element from question 2 on the x axis and atomic radius on the y-axis. Plot the points, connect them, and give the graph a title.

3

Write a claim to tell what does happen to the atomic radius as you move across a period/row on the periodic table.

3

Give Evidence from the graph to support your claim.

3

Reasoning: Explain why the trend works this way. Be sure to discuss the effect of Zeff and electron shielding in your work.