Transition elements possess partially filled d orbitals, while main group elements feature completely filled s and p orbitals.

Transition elements are located in the d-block of the periodic table and are characterized by their partially filled d orbitals. This unique electron configuration enables them to exhibit multiple oxidation states and a diverse array of chemical properties. For instance, iron can exist as either $Fe^{2+}$ or $Fe^{3+}$ ions, both of which play crucial roles in biological processes, such as oxygen transport in hemoglobin.

In contrast, main group elements reside in the s and p blocks of the periodic table, where their s and p orbitals are fully occupied. As a result, these elements are generally less reactive than transition elements and tend to form fewer oxidation states. A prime example is carbon, which can form a maximum of four covalent bonds and is a fundamental component of organic molecules like glucose.

Moreover, the electron configuration of transition elements facilitates the formation of complex ions and coordination compounds. In these compounds, a central metal ion is surrounded by ligands—molecules or ions that donate a pair of electrons to the metal. This ability allows transition elements to create vibrant and colorful compounds, contributing significantly to various biological systems, including enzyme function.

In summary, the differences in electron configurations between transition elements and main group elements stem from the presence of partially filled d orbitals in transition elements. This characteristic leads to a broader spectrum of chemical properties and the capacity to form complex ions and coordination compounds.