Electronic Configuration of Scandium (Sc)

• Element: Scandium
• Symbol: Sc
• Atomic Number (Z): 21
• This means a neutral Scandium atom has exactly 21 electrons that need to be arranged into energy levels (orbitals).

Following the Aufbau Principle (which states electrons fill lower energy orbitals first), we fill the 21 electrons in this exact order:

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹

Note: Notice that the 4s orbital is filled before the 3d orbital. This is because 4s has a slightly lower energy level than 3d.

Writing the full sequence is tedious. Chemists use a shortcut by using the closest Noble Gas that comes before Scandium.

• The noble gas before Sc is Argon (Ar), which has 18 electrons (1s² 2s² 2p⁶ 3s² 3p⁶).
• So, we can replace the first 18 electrons with [Ar].

Shorthand Configuration: [Ar] 4s² 3d¹ (or [Ar] 3d¹ 4s²)

In chemical reactions, Scandium almost exclusively forms a +3 ion ($Sc^{3+}$). It does this by losing 3 electrons.

• Rule: Electrons are always removed from the outermost shell first (the 4s shell), followed by the 3d shell.
• It loses two from 4s and one from 3d.
• Configuration of $Sc^{3+}$: [Ar] (It achieves a perfectly stable noble gas configuration).