Explain that Group 1 elements have one electron in their outer shell.

Group 1 elements, known as alkali metals, are characterized by having one electron in their outer shell. This single outer-shell electron is responsible for their high reactivity, as these elements tend to lose this electron easily during chemical reactions. The presence of only one outer electron leads to similar chemical properties among Group 1 elements, such as their vigorous reactions with water and halogens. Understanding this electron configuration is crucial for predicting their behavior in various chemical contexts.