Question

Why are copper and chromium exceptions to the aufbau principle?

Answer 1

For any isolated element , they must want to get stable. And we also know that the full filled orbital is more stable than half filled orbital and half filled orbital is more stable than partially filled orbital.In case of Cr and Cu 3d5 and 4s1 and 3d10 4s1 respectively electronic configuration is found ...Both is more stable ...But when filled by aufbau principle they found that less stable than this configuration.