Track shell filling and infer valence behavior
Three steps, the way the exam actually works: work through the lab, write down your own observations, then answer a 6-point free response. What you recorded goes to the grader with your writing, so a conclusion that does not follow from your own evidence will cost you the point — exactly as it would with a real reader.
Run the investigation
- 1Build the neutral atoms for oxygen, sodium, magnesium, and chlorine.
- 2Record how many electrons occupy each shell for each atom.
- 3Record the number of valence electrons for each atom.
- 4Compare which atoms would need to gain or lose fewer electrons to reach a stable outer shell.
Booting the lab…
Record what you found
This is your reading of the source, not ours. The grader sees them, so your conclusions have to follow from what you actually recorded.
| O shell distribution | |
|---|---|
| Na shell distribution | |
| Mg shell distribution | |
| Cl shell distribution | |
| Valence electrons in Na | |
| Valence electrons in Cl |
Answer the free response
The shell model is simple, but it is enough to explain much of periodic chemistry. (a) Using your recorded shell distributions, explain why sodium and magnesium are metals while oxygen and chlorine are nonmetals. (b) Predict the ion each would most commonly form and justify each prediction by the fewest-electron route to a stable outer shell. (c) Explain why sodium is more chemically similar to lithium than to magnesium even though sodium and magnesium are in the same period. (d) State one important limitation of the Bohr shell model for real atoms, while also explaining why it still works for AP-level periodic trends.
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