Why do nitrogen group elements have similar chemical behavior?

The similar chemical behavior of nitrogen group elements (Group 15) is primarily rooted in the common features of their electronic configurations.2

Each element in this group possesses five electrons in its outermost shell. This configuration consists of a completely filled outer s orbital (containing two electrons) and three half-filled outer p orbitals. Because these three p orbitals are half-filled, they can interact with the orbitals of other atoms to form three covalent bonds.1

Additionally, after forming these three bonds, each atom retains an unshared, or lone, pair of electrons. This lone pair allows the molecules to act as electron pair donors in the formation of complexes and molecular addition compounds. While the elements exhibit a wide range of physical states and properties—transitioning from nonmetals like nitrogen and phosphorus to metalloids and finally the metal bismuth—these shared structural characteristics in their valence shells provide the fundamental basis for their chemical similarities.12