According to international naming conventions, groups are numbered 1 through 18 from the first left column (alkali metals) to the right last column (rare gases). Previously, they were numbered in Roman order. In the United States (and some other countries) in the past, groups were classified as “A” if the group contained only class s or p, or “B” if the group contained class d. Roman numbers are in units of column order from left to right (for example, the 4th column is the IVB group, and the 14th column is IVA).
The groups 8, 9, and 10 are grouped together into a large group VIIIB. The old IUPAC standard that used to circulate in Europe is similar, except that the letter “A” is used if the group is before 10 and “B” is used for group 10 or later; in addition, group VIIIB here is called group VIII while group VIIIA is group 0. In 1988, the new IUPAC naming system became effective, and the old group names according to Roman numerals were removed, [15] but still exists in some countries like Vietnam. Refer to the methods of naming old and new groups in the table below
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