Origin and use of the term metalloid antimony and tellurium, was recorded merely on a 'sometimes' basis. Use of the term metalloid subsequently underwent a period of great flux up to 1940. Consensus as to its application to intermediate or borderline elements did not occur until the ensuing years, between 1940 and 1960. In 1947, Pauling included a reference to metalloids in his classic and influential textbook, "General chemistry: An introduction to descriptive chemistry and modern chemical theory." He described them as 'elements with intermediate properties ... occupy[ing] a diagonal region [on the periodic table], which includes boron, silicon, germanium, arsenic, antimony, tellurium, and polonium.' In 1959
Metalloid (∆H) greater than ~42 kJ/mol are metallic when liquid. Such elements include boron, silicon, germanium, antimony, selenium, and tellurium. Estimated values for ∆H of diatomic astatine are 50 kJ/mol or higher; diatomic iodine, with a ∆H of 41.71, falls just short of the threshold figure. "Like typical metals, it [astatine] is precipitated by hydrogen sulfide even from strongly acid solutions and is displaced in a free form from sulfate solutions; it is deposited on the cathode on electrolysis." Further indications of a tendency for astatine to behave like a (heavy) metal are: "... the formation of pseudohalide compounds ... complexes