I am assuming you mean to ask why elements go into specific groups
Elements that have the same number of valence electrons are put into the same group. Because they all have the same number of valence electrons, it could also be said that elements are put into groups based on their chemical properties.
Because their chemical properties are mainly dependent on their valence (outer-most) electrons ... which does make a pattern on the Periodic Table.
There are 18 groups in the Periodic Table of elements.
the Periodic Table of elements
there are no compounds on a periodic table. only elements are placed in the periodic table and they are grouped by similar attributes
he drew up a table that grouped elements according to their atomic weights, his table became the basis for the periodic table of elements used today.
MOSLEY
Metals
Group are based on similar properties. The elements having same chemical properties are grouped together.
Group I, the Alkalai Metals
The periodic table lists the elements that are currently known. They are grouped by atomic weight in most cases, by properties, and go in order by number of protons in the nucleus.
Properties of elements are periodic function of atomic number. Elements with same chemical properties are grouped together.
Periodic table show that elements have properties which are periodic in nature. These properties can be grouped together.
The answer is: noble gases