What does the group number mean on the periodic table of elements?

Group number:

• In the periodic table, there are seven periods and eighteen groups.
• The periodic table has eight main groups: $1,2,13,14,15,16,17,\mathrm{and}18$ ( $\mathrm{Ia},\mathrm{IIa},\mathrm{IIIa},\mathrm{IVa},\mathrm{Va},\mathrm{VIa},\mathrm{VIIa},\mathrm{and}0,\mathrm{respectively}$).
• The group number represent the valence electron (s) present in the elements belonging to a specific group.
• The chemical/physical properties of some elements belonging to the same group are identical.
• Examples: Group $1$ is known as Alkali metals, Group $2$ is known as Alkaline earth metals, and Group $17$ is known as Halogens.