What happens to Group 7 elements as atomic number increases?

As atomic number increases in Group 7 elements, also known as the halogens, reactivity decreases. This trend can be attributed to several factors related to atomic structure and electron configuration.

Halogens have seven electrons in their outermost shell and tend to gain one electron to achieve a stable octet configuration. As you move down the group from fluorine to iodine, the atomic size increases due to the addition of more electron shells. This increase in size results in a greater distance between the outermost electrons and the nucleus. Consequently, the valence electrons experience weaker electrostatic attractions to the nucleus, making it more challenging for these elements to gain an additional electron.

Moreover, the presence of additional inner electron shells leads to increased shielding effects, which further reduce the effective nuclear charge experienced by the outer electrons. As a result, the ability of the halogen atoms to attract and gain an electron decreases, leading to diminished reactivity as you go from fluorine to astatine.

This understanding of atomic structure and trends in reactivity is fundamental in chemistry and highlights the predictable nature of periodic trends within the elements.