Elements within the same group of the Periodic Table exhibit similar properties because they possess the same number of electrons in their outermost shell, known as valence electrons.

The Periodic Table organizes elements into groups and periods. The groups are arranged vertically, and the elements within each group share comparable chemical properties. This similarity arises from the fact that they have the same number of valence electrons, which are critical in determining an element’s chemical behavior as they are involved in chemical reactions.

For instance, elements in Group 1, referred to as alkali metals, each contain one electron in their outer shell. This configuration makes them highly reactive, as they tend to lose that single electron to attain a stable electron arrangement. Consequently, alkali metals react vigorously with water and halogens, forming ionic compounds with similar characteristics.

Conversely, elements in Group 0, known as noble gases, have completely filled outer shells. This configuration renders them highly stable and largely unreactive, as they neither need to gain, lose, nor share electrons to achieve stability. As a result, noble gases exhibit similar properties, including being colorless and odorless gases that do not readily participate in chemical reactions.

In conclusion, the number of valence electrons, which remains consistent among elements in the same group, is crucial in determining their chemical properties. This is why elements within the same group of the Periodic Table demonstrate similar behaviors and reactions.