Predict properties of Group 7 elements from trends down the group.

The properties of Group 7 elements, known as halogens, can be predicted based on trends observed down the group. As you move down Group 7, the relative molecular mass increases, and the melting and boiling points also rise. Reactivity decreases down the group due to the increasing atomic size, which makes it harder for the outer electrons to attract additional electrons for bonding. Therefore, elements like fluorine are more reactive than iodine. Understanding these trends allows for predictions about the behavior and characteristics of halogens.