What does the group number of an element determine?

The group number of an element in the periodic table primarily indicates the valency and the arrangement of electrons in the outer shell of the atoms of that element. Elements in the same group share similar chemical properties because they have the same number of valence electrons, which directly influences how they bond with other elements.

For instance, group 1 elements (alkali metals) all have one electron in their outermost shell, making them highly reactive and giving them a valency of +1. Similarly, group 2 elements have two electrons in their outer shell and typically exhibit a valency of +2. This pattern continues across the periodic table, with groups such as the halogens and noble gases having different outer electron configurations that determine their reactivity and bonding behavior.

Understanding the group number helps predict the element's behavior in chemical reactions, which is crucial in the study of chemistry.