![]() | Numeration |
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The numeration is the way of numbering the 18 groups of the periodic table. You can change the numeration to IUPAC, old IUPAC and CAS or switch it off entirely.
No Numeration: if this option is active, no period-numeration will be in effect.
Show IUPAC (default): the IUPAC is the International Union of Pure and Applied Chemistry. This is an organization which defines most of the standards for chemical concerns. The new IUPAC system numbers each column with Arabic numbers from 1 (one) through 18 (eighteen).
Show CAS: the CAS is the Chemical Abstracts Service. In the CAS system the letters A and B were designated to main group elements (A) and transition elements (B). Though the IUPAC numeration is the official, the CAS numeration is what is still used in classrooms and laboratories.
Show Old IUPAC: the old IUPAC system labeled columns with Roman numerals followed by either the letter 'A' or 'B'. Columns were numbered such that columns one through seven were numbered 'IA' through 'VIIA', columns 8 through 10 were labeled 'VIIIA', columns 11 through 17 were numbered 'IB' through 'VIIB' and column 18 was numbered 'VIII'. Because of the confusion the old IUPAC and the CAS system created, the IUPAC adopted their new system.
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