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As such these elements are currently known only by

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have not yet been confirmed. As such these elements are currently known only by their systematic element names, based on their atomic numbers. [4] No element heavier than einsteinium (element 99) has ever been observed in macroscopic quantities in its pure form. [5] No elements past 118 have been synthesized as of 2012. [6] Grouping methods Groups Main article: Group (periodic table) A group or family is a vertical column in the periodic table. Groups usually have more significant periodic trends than periods and blocks, explained below. Modern quantum mechanical theories of atomic structure explain group trends by proposing that elements within the same group generally have the same electron configurations in their valence shell. [7] Consequently, elements in the same group tend to have a shared chemistry and exhibit a clear trend in properties with increasing atomic number. [8] However in some parts of the periodic table, such as the d-block and the f-block, horizontal similarities can be as important as, or more pronounced than, vertical similarities. [9][10][11] Under an international naming convention, the groups are numbered numerically from 1 to 18 from the leftmost column (the alkali
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6/2/13 11:44 AM Periodic table - Wikipedia, the free encyclopedia Page 4 of 17 http://en.wikipedia.org/wiki/Periodic_table V · T · E (//en.wikipedia.org/w/index.php?title=Template:Periodic_table_(group_names)&action=edit) metals) to the rightmost column (the noble gases). [12] Previously, they were known by roman numerals. In America, the roman numerals were followed by either an "A" if the group was in the s- or p-block, or a "B" if the group was in the d-block. The roman numerals used correspond to the last digit of today's naming convention (e.g. the group 4 elements were group IVB, and the group 14 elements was group IVA). In Europe, the lettering was similar, except that "A" was used if the group was before group 10, and "B" was used for groups including and after group 10. In addition, groups 8, 9 and 10 used to be treated as one triple-sized group, known collectively in both notations as group VIII. In 1988, the new IUPAC naming system was put into use, and the old group names were deprecated. [13] Some of these groups have been given trivial (unsystematic) names, as seen in the table to the right, although some are rarely used. Groups 3–10 have no trivial names and are referred to simply by their group numbers or by the name of the first member of their group (such as 'the scandium group' for Group 3), since they display fewer similarities and/or vertical trends. [12] Elements in the same group tend to show patterns in atomic radius, ionization energy, and electronegativity. From top to bottom in a group, the atomic radii of the elements increase. Since there are more filled energy levels, valence electrons are found farther from the nucleus. From the top, each successive element has a lower ionization energy because it is easier to remove an electron since the atoms are less tightly bound. Similarly, a group has a top to bottom decrease in electronegativity due to an increasing distance between valence electrons and the nucleus.
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