Scandium is not regarded as a transition metal because its ion has
Answer Details
Scandium is not regarded as a transition metal because its ion has no electron in the d-orbital.
To understand this, let's first define a transition metal. A transition metal is defined as an element that has an incomplete d-subshell in either its elemental form or in any of its common oxidation states.
When Scandium (Sc) loses electrons to form its most common ion (Sc3+), it loses three electrons. These electrons are removed from the 4s and 3d orbitals. The electron configuration for Scandium is [Ar] 3d1 4s2. Upon losing three electrons to form Sc3+, the resulting electron configuration is [Ar], which means there are:
No electrons in the 3d sublevel
No electrons in the 4s sublevel
As a result, there are no electrons in the d-orbital of the Scandium ion, which does not meet the criteria for a transition metal.