What are the vertical columns in the periodic table?

The vertical columns in the periodic table are called “Groups”. There are eighteen groups in the periodic table.

Naming of these groups

The groups in the periodic table are numbered 1 to 18 according to the latest recommendations of IUPAC. However, the older system of naming the groups is still important enough to be remembered. In the old system, the groups were named as follows:

IA, IIA, IIIB, IVB, VB, VIB, VIIB, VIIIB, IB, IIB, IIIB, IVA, VA, VIIA, VIII group

As you may notice, there are only 16 groups in the above system. This is because the group VIIIB contains three vertical columns which are the 8^th, 9^th and 10^th columns according to the current naming system. The old system of naming of the groups is significant because it denotes the number of electrons present in the outer shell of the atoms of the elements present in that group. For example, group IA elements have 1 electron in their outer shells, and group VIIA elements have 7 electrons in their outer shells.

Characteristics of groups (vertical columns) in the periodic table

All elements present in the same group of the periodic table contain the same number of valence electrons. As a result, their chemical properties are similar and they show a gradual variation of many characteristics when going down a group.
For example, the alkali metals in the first group of the periodic table all have 1 valence electron. Their chemical properties are also similar. They react with water to liberate hydrogen gas and to produce their respective hydroxides.

Groups are also referred to by some common names in the periodic table. These are alkali metals (the first group), alkali earth metals (the second group), halogens (the third group), etc.

The group containing the most number of elements in the periodic table is the third group, as it contains the Lanthanide and the Actinide series of elements, each of which are a group of 15 elements. These two series of elements are placed at the bottom of the periodic table in order to not distort its shape.