Why is scandium outer electron configuration #4s^2 3d^1# and not just #3d^3#?

Answer 1

Because God wanted it that way...?

Qualitatively, we can assume that the #4s# orbital should be slightly stabilized with respect to the #3d# orbitals in that the #s# orbitals have some small probability of occurrence near the scandium nucleus. There are some very few examples of reduced, i.e. #"hypovalent"# scandium metal complexes, and their electronic structure is not very well explained.
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Answer 2

See below:

The 3d sub level is just below the 4s sub level for the 1st transition series so you might correctly think that these should fill first to give #sf(3d^3)#.

Nevertheless, multiple forces are at play here: a factor known as "Exchange Energy" stabilizes electrons in the same subshell with parallel spins; this is a quantum mechanical effect for which there is no classical counterpart.

The coulombic repulsion that electrons in the same sub shell experience is another counterfactor at work. In this scenario, the extra stability provided by the exchange energy is outweighed by the coulombic repulsion, which tends to "push" the electrons up into the larger 4s orbital where repulsion is less.

Accordingly, when ions form, the outer electrons, or 4s, are the first to be lost and define the atomic radius of the atom.

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Answer 3

The electron configuration of scandium is 4s² 3d¹ instead of just 3d³ because of the Aufbau principle, which states that electrons fill orbitals starting from the lowest energy level to the highest. In the case of scandium, filling the 4s orbital first before the 3d orbitals results in a lower overall energy configuration.

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

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