How are columns in the periodic table arranged?

The arrangement of columns in the periodic table is based on the properties of the elements within those columns. Elements that are grouped together in the same column, also known as groups, exhibit similar chemical behaviors and physical properties. This similarity arises from the fact that elements within a group have the same number of electrons in their outermost shell, which directly influences their reactivity and the types of bonds they can form.

For example, alkali metals are found in Group 1 and have one electron in their outermost shell, making them highly reactive and giving them similar reactions with water. Similarly, halogens in Group 17 have seven electrons in their outer shell and exhibit consistent reactivity trends with other elements.

The other arrangements mentioned, such as atomic size or boiling points, do not dictate the grouping of elements in the same way that similar properties do. The periodic table is specifically designed to highlight these relationships among elements, which helps in predicting their behavior in chemical reactions.