Scandium is not regarded as a transition metal because its ion has

1. Analyze the Question

The question asks why Scandium (Sc) is excluded from the strict definition of a transition metal, specifically focusing on the electronic configuration of its ion.

2. Explain the Concept

In chemistry, a transition metal is defined as an element that has an incomplete (partially filled) d-subshell in its neutral state or in at least one of its common oxidation states.

• Scandium (Sc) has an atomic number of 21.
• Its electronic configuration is: $1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^1$.
• When Scandium forms an ion, it loses its three outermost electrons (two from the $4s$ orbital and one from the $3d$ orbital) to achieve a stable noble gas configuration ($Sc^{3+}$).
• The configuration of the $Sc^{3+}$ ion is: $1s^2 2s^2 2p^6 3s^2 3p^6$.

3. Show the Solution

• Step 1: Look at the $Sc^{3+}$ ion configuration. You will notice that the $3d$ subshell is now completely empty ($3d^0$).
• Step 2: Compare this to the definition of a transition metal. Since the $Sc^{3+}$ ion has no electrons in the d-orbital, it does not meet the criteria of having a "partially filled d-orbital" in its stable ionic state.
• Step 3: Evaluate the options. • Option A: "no electron in the d-orbital" matches our finding ($3d^0$). • Option B: "a partially filled d-orbitals" is incorrect because the ion has zero electrons in the d-orbital. • Option C & D: These refer to the $4s$ orbital, which is not the defining factor for transition metal classification (the d-orbital is).

4. Identify the Answer

5. Exam Tip

Memory Trick: Remember the "d-orbital rule." Think of transition metals as elements that have "d-electrons to spare." If an element (like Scandium or Zinc) loses its d-electrons to become stable, it loses its "transition metal" status in that specific ionic form.