Vertical columns (major classes or divisions) into which elements are arranged in the periodic table of elements. Elements in a group have similar configurations of their Outermost shell of electrons in an atom in its ground state. Click on Term to Read More electrons, which gives them similar properties. There are three common numbering systems for these groups. (1) The IUPAC Definable part of the universe that can be open, closed, or isolated. An open system exchanges both matter and energy with its surroundings. A closed system can only exchange energy with its surroundings; it has walls through which heat can pass. An isolated system cannot exchange energy or matter with, which numbers each column from 1–18. (2) The old IUPAC system, which labeled columns with Roman numerals followed by either ‘A’ or ‘B’. Columns were numbed such that columns 1–7 were numbered ‘IA’ through ‘VIIA’, columns 8–10 were labeled ‘VIIIA’, columns 11–17 were numbered ‘IB’ through ‘VIIB’ and column 18 was numbered ‘VIII’. (3) The CAS system, which also used Roman numerals followed by ‘A’ or ‘B’. This method, however, labeled columns 1 and 2 as ‘IA’ and ‘IIA’, columns 3–7 as ‘IIIB’ through ‘VIB’, column 8–10 as ‘VIII’, columns 11 and 12 as ‘IB’ and ‘IIB’ and columns 13–18 as ‘IIIA’ through ‘VIIIA’. Because of the confusion the old IUPAC and the CAS system created, the IUPAC adopted their new system; this is the preferred system.
Some or all content above used with permission from J. H. Wittke.