Question #d8aba

1 Answer
Dr. Hayek
Oct 5, 2015

See explanation.

Explanation:

Follow this chart, you will see why.
enter image source here

The correct one is: #1s^2, 2s^2, 2p^6, 3s^2, 3p^6, 4s^1#

You should follow the direction of the arrows.

The real reason for filling 4s before 3d is that there is a slight probability of finding an electron in the less energetic part of 4s subshell than in the 3d subshell, that is why we consider 4s is less energetic than 3d and it gets filled before.
enter image source here

Even though the electron in 4s spends most of its time further from the nucleus, but its more probable to be closer to the nucleus than a 3d electron.

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