14 electron affinity also shows a slight trend across

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[14] Electron affinity also shows a slight trend across a period. Metals (left side of a period) generally have a lower electron affinity than nonmetals (right side of a period), with the exception of the noble gases. [18] Blocks Main article: Block (periodic table) Because of the importance of the outermost electron shell, the different regions of the periodic table are sometimes referred to as blocks , named according to the subshell in which the "last" electron resides. [19] The s-block comprises the first two groups (alkali metals and alkaline earth metals) as well as hydrogen and helium. The p-block comprises the last six groups which are groups 13 to 18 in IUPAC (3A to 8A in American) and contains, among other elements, all of the metalloids. The d-block comprises groups 3 to 12 in IUPAC (or 3B to 2B in American group numbering) and contains all of the transition metals. The f-block, usually offset below the rest of the periodic table, comprises the lanthanides and actinides. [20] Other conventions and variations In presentations of the periodic table, the lanthanides and the actinides are customarily shown as two additional rows below the main body of the table, [21] with placeholders or else a selected single element of each series (either lanthanum or lutetium, and either actinium or lawrencium, respectively) shown in a single cell of the main table, between barium and hafnium, and radium and rutherfordium, respectively. This convention is entirely a matter of aesthetics and formatting practicality; a rarely used wide-formatted periodic table inserts the lanthanide and actinide series in their proper places, as parts of the table's sixth and seventh rows (periods). Periodic table with f-block separated (left) and inline (right) Some periodic tables include a dividing line, or equivalent, between metals and nonmetals. [22] Various other categories of elements may also be highlighted on a periodic table including, for example, transition metals, post-transition metals, or metalloids. [23] Specialized groupings such as the refractory metals and the noble metals, which are subsets (in this example) of the transition metals, are also known [24] and occasionally denoted. [25] Periodic trends Main article: Periodic trends Electron configuration Main article: Electronic configuration
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6/2/13 11:44 AM Periodic table - Wikipedia, the free encyclopedia Page 6 of 17 http://en.wikipedia.org/wiki/Periodic_table Approximate order in which shells and subshells are arranged by increasing energy according to the Madelung rule. Periodic table trends. Arrows point at increase. Atomic number plotted against atomic radius [n 3] The electron configuration or organisation of electrons orbiting neutral atoms shows a recurring pattern or periodicity. The electrons occupy a series of electron shells (numbered shell 1, shell 2, and so on). Each shell consists of one or more subshells (named s, p, d, f and g). As atomic number increases, electrons progressively fill these shells and subshells more or less according to the Madelung rule or energy ordering rule, as shown in the diagram to the right. The electron configuration for neon, for example, is 1s
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