Nitrogen Group Element | Properties, Uses, & List | Britannica

Similarities in orbital arrangement

In the periodic table, each of the nitrogen group elements occupies the fifth position among the main group elements of its period, a position designated 15. In terms of the electronic configuration of its atoms, each nitrogen group element possesses an outermost shell of five electrons. In each case, these occupy an outer s orbital completely (with two electrons) and contribute one electron to each of the three outer p orbitals (the orbitals being electron regions within the atom and the letter designations, s, p, d, and f, being used to designate different classes of orbital). The arrangement of outer electrons in the atoms of the nitrogen elements thus provides three half-filled outer orbitals that, by interaction with half-filled orbitals of the atoms of other elements, can form three covalent bonds. The other atoms may attract the shared electrons either more or less strongly than do the nitrogen group atoms; therefore the latter may acquire either positive or negative charges and exist in oxidation states of +3 or −3 in their compounds. In this respect, the nitrogen elements are alike.

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Another similarity among the nitrogen elements is the existence of an unshared, or lone, pair of electrons, which remains after the three covalent bonds, or their equivalent, have been formed. This lone pair permits the molecule to act as an electron pair donor in the formation of molecular addition compounds and complexes. The availability of the lone pair depends upon various factors, such as the relative size of the atom, its partial charge in the molecule, the spatial characteristics of other groups in the molecule, and the as-yet poorly understood phenomenon called the “inert pair effect.” This effect consists of a tendency for the paired s electrons in the outermost shell of the heavier atoms of a major group to remain chemically unreactive. Because of it, the electron pair-donating ability of the nitrogen group elements is not uniform throughout the group; it is probably greatest with nitrogen, less with the intermediate elements, and nonexistent with bismuth.