While most chemists agree on what is a metal and what is a non-metal there is a disagreement with respect to what is a metalloid and what is a transition metal. It is believed that this problem can be solved if two new terms are adopted: typical and less typical metals. These new terms will also help reconcile the European Periodic Table versus the North American regarding numbering of groups as well as the IUPAC numbering which could be as well (...) abandoned in favour of group names as will be shown in the manuscript. (shrink)

The usefulness of isoelectronic series (same number of total electrons and atoms and of valence electrons) across Periods is often overlooked. Here we show the ubiquitousness of isoelectronic sets by means of matrices, arrays, and sequential series. Some of these series have not previously been identified. In addition, we recommend the use of the term valence-isoelectronic for species which differ in the number of core electrons and pseudo-isoelectronic for matching (n) and (n + 10) species.

Similarities in properties among pairs of metallic elements and their compounds in the lower-right quadrant of the Periodic Table have been named the ‘Knight’s Move’ relationship. Here, we have undertaken a systematic study of the only two ‘double-pairs’ of ‘Knight’s Move’ elements within this region: copper-indium/indium-bismuth and zinc-tin/tin-polonium, focussing on: metal melting points; formulas and properties of compounds; and melting points of halides and chalcogenides. On the basis of these comparisons, we conclude that the systematic evidence for ‘Knight’s Move’ relationships (...) derives from similarities in formulas and properties of matching pairs of compounds in the same oxidation state. Physical properties, such as melting points, do not provide consistent patterns and trends and hence should not be considered as a common characteristic of this relationship. (shrink)