This is according to the "old" IUPAC system, which (in theory at least) was replaced in 1990 by a new IUPAC system. (IUPAC stands for the International Union of Pure and Applied Chemistry.)
The new IUPAC system replaced the "old" IUPAC system, which was commonly used in Europe, and the CAS system, which was favoured in America.
The new IUPAC system numbers the groups from 1 to 18, and the noble or inert (or rare) gases are classified as Group 18.
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