What groupings on the periodic table are made up of elements that react similarly?
1.groups/families
2.metals, nonmetals, metalloids
3.periods
4.series

elements are arranged in the periodic table in order of increasing atomic number. They are classified into rows and columns.

Rows are called periods and columns are called groups.

atomic number is the number of protons. Elements with same number of energy shells fall into the same period and elements with same number of valence electrons fall into the same group.

Valence electrons take part in the chemical reactions. Therefore electrons are responsible for the chemical properties of the elements.

So elements with same number of valence electrons have similar chemical properties.

Elements with same number of valence electrons fall into the same group.

Therefore elements of the same group react similarly.

answer is 1. groups

there are no atoms