Final answer:
Predicting the charge of a metal with a d-subshell can be difficult due to the variable electron configurations, especially for transition metals. Sc³⁺, Ni²⁺, Cu²⁺, and Zn²⁺ are examples that exhibit the diversity in possible charges and colors in their complexes.
Step-by-step explanation:
When a metal has a d-subshell, predicting its charge can sometimes be challenging. This is due to the variable electron configurations metals can adopt when they form ions. Transition metals, in particular, have a d-subshell that can be partially filled, empty (d°), or fully filled (d¹⁰). For instance, the metal ions like Sc³⁺ (d°), Ni²⁺ (d¸) with two unpaired electrons, Cu²⁺ (d¹) with one unpaired electron, and Zn²⁺ (d¹⁰) with no unpaired electrons illustrate the variety of possible electronic configurations.
Metals with a partially filled d-subshell typically form colored complexes, whereas those with an empty or filled d-subshell often result in colorless complexes. The variation in these configurations results from the energy levels of the orbitals and the specific electron arrangement that minimizes repulsion. In the cases of metals with d⁸-d¹⁰ configurations, fewer possible arrangements of d electrons exist, making their charge states somewhat more predictable than those of metals with fewer than eight d electrons.