In the periodic table, the vertical columns of elements are called groups.
The modern periodic table contains 18 numbered groups, running from the alkali metals in Group 1 to the noble gases in Group 18. Elements within a group often have similar chemical properties because they have related outer-electron arrangements.
Groups are commonly confused with periods, which are the horizontal rows. Blocks are larger regions—such as the s-, p-, d-, and f-blocks—based on the type of atomic orbital being filled. The word “family” is also sometimes used informally for a group, especially for sets such as the halogens or noble gases.
IUPAC’s 1-to-18 numbering system was introduced to replace older Roman-numeral naming systems, which varied between regions.