The previous page is sending you to https://www.quora.com/How-does-filling-4s-and-3d-orbitals-work-For-example-I-dont-understand-why-the-electron-configuration-for-Cu-is-4s1-3d10-instead-of-4s2-3d9.

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