Princípios de agrupamento de elementos químicos dentro do sistema periódico

Within the Periodic Table (Table 1.1) the chemical elements can be grouped together in blocks according to occupancy of their outermost, or valence shell, atomic orbitals. Thus hydrogen and the alkali metals, lithium to francium, with a half-filled outer s subshell, together with heli- um and the alkaline earth metals, beryllium to radium, with a filled outer s subshell, comprise the s-block elements (Figure 1.1). Similarly, elements with a partly or fully filled outer p subshell comprise the p-block ele- ments. That is the block from boron through to neon down to thallium through to radon. Together the s- and p-block elements comprise the main group elements. Between these two blocks of elements there are two further blocks containing the transition elements. Strictly speaking, the term transition element applies to an element with a partly filled d or f subshell and so excludes those with do or dl0 and fo or fI4 electron configurations. However, it is convenient to include copper, silver and gold in this clas- sification as these elements commonly form ions with partly filled d sub- shells. Although their neutral atoms have dIo electron configurations, it is the chemistry of their ions which is of primary interest here. Similar arguments apply to yfterbium and nobelium.

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