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Numbering the Columns of the Periodic Table

Bruce Wilson
Product Development Department
Carolina Biological Supply Company

Mendeleev's invention of the Periodic Table ranks as one of the greatest achievements in chemistry. More than a hundred years after its inception, the Periodic Table remains one of the most useful references in the chemistry classroom and laboratory. The invariant nature of the Table attests to its power. In its history, the Periodic Table has been changed only once, when Moseley arranged the elements by atomic number.

Despite its success, the Periodic Table suffers from inconsistent column labels. At present, there are 3 versions of the Periodic Table widely used, each with its own unique column headings. The 3 formats are the Chemical Abstract Service (CAS) table, the old International Union of Pure and Applied Chemistry (IUPAC) table, and the new IUPAC table.

Mendeleev organized the elements not only by atomic mass but also by chemical reactivity. In this system, the transition metals were placed in the same group as the main group elements. These groups were labeled with Roman numerals according to the oxidation states of the elements in their oxides. Thus, aluminum was assigned the same group number, III, as scandium. To differentiate the main group elements from the transition metals, groups were labeled with the letters A and B. Unfortunately, the British and North Americans chose to use opposite conventions. For example, aluminum became a Group IIIB element in Britain, which adopted what is now the old IUPAC format, but it became a Group IIIA element in North America, where the CAS version is used.

In an attempt to eliminate this confusion, the IUPAC has proposed new column headings. In the new IUPAC Periodic Table, columns are numbered from 1 to 18 with Arabic numerals. These group numbers correspond to the number of s, p, and d orbital electrons added since the last noble gas element. Unfortunately, the system fails for the elements in the first 3 periods. For example, aluminum, in the column numbered 13, has only 3 s, p, and d orbital electrons. Nevertheless, the American Chemical Society has adopted the new IUPAC form of the Periodic Table.

As the debate continues, the knowledge of generations of chemists rests securely in the columns and rows of the Periodic Table, which, no matter its final form, will continue to serve chemistry and chemists well.

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Numbering the Columns of the Periodic Table
*Bruce Wilson* Product Development Department Carolina Biological Supply Company Mendeleev's invention of the Periodic Table ranks as one of the greatest achievements in chemistry. More than a hundred years after its inception, the Periodic Table remains one of the most useful references in the chemistry classroom and laboratory. The invariant nature of the Table attests to its power. In its history, the Periodic Table has been changed only once, when Moseley arranged the elements by atomic number. Despite its success, the Periodic Table suffers from inconsistent column labels. At present, there are 3 versions of the Periodic Table widely used, each with its own unique column headings. The 3 formats are the Chemical Abstract Service (CAS) table, the old International Union of Pure and Applied Chemistry (IUPAC) table, and the new IUPAC table. Mendeleev organized the elements not only by atomic mass but also by chemical reactivity. In this system, the transition metals were placed in the same group as the main group elements.	These groups were labeled with Roman numerals according to the oxidation states of the elements in their oxides. Thus, aluminum was assigned the same group number, III, as scandium. To differentiate the main group elements from the transition metals, groups were labeled with the letters A and B. Unfortunately, the British and North Americans chose to use opposite conventions. For example, aluminum became a Group IIIB element in Britain, which adopted what is now the old IUPAC format, but it became a Group IIIA element in North America, where the CAS version is used. In an attempt to eliminate this confusion, the IUPAC has proposed new column headings. In the new IUPAC Periodic Table, columns are numbered from 1 to 18 with Arabic numerals. These group numbers correspond to the number of s, p, and d orbital electrons added since the last noble gas element. Unfortunately, the system fails for the elements in the first 3 periods. For example, aluminum, in the column numbered 13, has only 3 s, p, and d orbital electrons. Nevertheless, the American Chemical Society has adopted the new IUPAC form of the Periodic Table. As the debate continues, the knowledge of generations of chemists rests securely in the columns and rows of the Periodic Table, which, no matter its final form, will continue to serve chemistry and chemists well.

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