Transition Metals

The transition metals occupy the d-block in the center of the periodic table and display a distinctive cluster of properties that set them apart from main-group elements. A transition element is best defined as one that forms at least one stable ion with a partially filled $d$ subshell. This definition explains why zinc, although in the d-block, is often excluded: its only common ion, $Zn^{2+}$, has a full $d^{10}$ configuration. The characteristic behaviors of the transition metals, variable oxidation states, colored compounds, catalytic activity, and magnetism, all trace back to the involvement of $d$ electrons.

Variable oxidation states are a hallmark of transition metals. Because the $3d$ and $4s$ subshells are close in energy, a transition metal can lose different numbers of electrons