A relatively recent development in chemistry involves certain compounds of heavier pblock elements, such as silicon, indium, phosphorus, germanium, arsenic, antimony, and bismuth exhibiting behaviours typically associated with transition metal complexes. This phenomenon is linked to a small energy gap between their filled and empty molecular orbitals, which are the regions in a molecule where electrons reside and where they can be available for chemical reactions. In such compounds, this closer energy alignment allows for unusual reactivity with small molecules like hydrogen, ammonia, and ethylene and carbon dioxide, a characteristic previously observed primarily in transition metal compounds. These reactions could open new avenues in catalytic applications, offering potential for innovative chemical processes. ). 7 In, Tl and Bi are predominately basic; the remainder are amphoteric 8 In(I), Tl(I), Sn(II), Pb(II), Po(II) 9 Pauling's assessment of the nature of metalloids, in 1947, was misconceived. He said they were in the centre of his electronegativity scale, with electronegativity values close to 2. In fact, his scale ran from 0.7 to 4, giving a midpoint of 2.35, whereas the metalloids had values of 1.8 to 2.1 10 Being weakly acidic, B2O3 reacts with NaOH to form various borates; in its hydrated form (as H3BO3, boric acid) it reacts with sulfur trioxide, the anhydride of sulfuric acid, to form a bisulfate B(HSO4)3. As2O3, being weakly acidic, dissolves readily in alkaline solutions to give arsenites; it reacts as an anhydrous base with the acid anhydride SO3, yielding arsenic(III) sulfate, As2(SO4)3.