# Chapter 5 - Electron Configurations and the Periodic Table - Questions for Review and Thought - Topical Questions - Page 240c: 71a

$1s^22s^22p^6$

#### Work Step by Step

From the given information, we see that Al 3+ and Na+ are the two isoelectric species present, since they have the same number of electrons. We now write the electron configurations, using the information that we learned over the course of the chapter. Recall, we start at 1s and move up: $1s^22s^22p^6$

After you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.