Is 1s2 2s2 2p6 3s3 3d5 valid?

Answer 1

No. The symbol "s" denotes and electron energy level that can never contain more than two electrons, no matter how high the period number is . Therefore, "3s3" can never be part of a valid electron energy description; the only digits that can follow "s" are 1 and 2.

Answer 2

No, the electron configuration you provided (1s2 2s2 2p6 3s3 3d5) is not valid. The electron configurations must follow the Aufbau principle, which means filling orbitals from the lowest energy level to the highest. The correct electron configuration for a neutral atom with 28 electrons would be 1s2 2s2 2p6 3s2 3p6 4s2 3d8.

Answer 3

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