Final answer:
Copper is considered a transition metal not for its neutral atomic configuration, which has a full d-orbital, but because it forms Cu²+ ions with incomplete d orbitals, fulfilling the criteria for transition metals.
Step-by-step explanation:
A copper atom has a full d-orbital in its ground state ([Ar]3d¹⁰4s¹). However, its classification as a transition metal isn't due to its neutral ground state but rather to its +2 oxidation state, where it forms Cu²+ ions with an electronic structure of [Ar] 3d¹, representing an incomplete d orbital configuration. Transition metals are characterized by their ability to form stable ions with incompletely filled d orbitals, and although zinc and scandium are d-block elements, their ions do not show incomplete d orbitals after ionization; hence they are not considered as transition metals.
Meanwhile, copper (Cu) forms two ions; with Cu¹+ retaining a full d level, and more commonly, Cu²+ having an incomplete d level - making it a definitive transition metal. Copper's unique electronic configuration also contributes to the rich and complex chemistry commonly associated with transition metals, including multiple stable oxidation states and the formation of colored compounds through electron transitions within the d orbitals.