Arsenic, antimony and bismuth

   Arsenic vapour contains As₄ molecules, and the unstable yellow form of solid As probably also contains these units; at relatively low temperatures, Sb vapour contains molecular Sb₄. At room temperature and pressure, As, Sb and Bi are grey solids with lattice structures resembling that of black phosphorus (Figure 1.1c).

On descending the group, although intralayer bond distances increase as expected, similar increases in interlayer spacing do not occur, and the coordination number of each atom effectively changes from 3 (Figure 1.1c) to 6 (three atoms within a layer and three in the next layer). Arsenic, antimony and bismuth burn in air and combine with halogens.

    They are not attacked by non-oxidizing acids but react with concentrated HNO₃ to give H₃AsO₄ (hydrated As₂O₅), hydrated Sb₂O₅ and Bi(NO₃)₃ respectively, and with concentrated H₂SO₄ to produce As₄O₆, Sb₂ (SO₄)₃ and Bi₂(SO₄)₃ respectively. None of the elements reacts with aqueous alkali, but As is attacked by fused NaOH.