Physical properties

Down Group 15 from nitrogen to bismuth, the physical state changes from a diatomic gas (N2) to solids, atomic number and atomic mass rise steadily, and atomic radius increases from about 1.55 Å for nitrogen to 2.07 Å for bismuth as successive electron shells are added, even though the effective nuclear charge also increases. Density increases sharply down the group as the atoms become heavier and more metallic in packing, from nitrogen's very low gas-phase density (1.14 x 10^-3 g/cm3) up to bismuth's 9.79 g/cm3. Melting and boiling points generally rise down the group (with phosphorus's low melting point and easy sublimation behaviour as white phosphorus reflecting its molecular P4 lattice, in contrast to nitrogen's very low boiling point as a small diatomic molecule with only weak van der Waals forces). All five elements share the outer electronic configuration ns2 np3 (a half-filled p subshell, which is why they display a common oxidation state of +3 or +5, …