The previous page is sending you to https://www.khanacademy.org/science/ap-chemistry-beta/x2eef969c74e0d802:atomic-structure-and-properties/x2eef969c74e0d802:atomic-structure-and-electron-configuration/v/the-aufbau-principle.

 If you do not want to visit that page, you can return to the previous page.