The halogens are found in Group 17 of the periodic table and include fluorine F , chlorine Cl , bromine Br , iodine I , and astatine At . They have a general electronic configuration of ns^2 np^5, where n represents the principal quantum number energy level . This configuration means that halogens have seven valence electrons and require one more electron to achieve a stable, full outer electron shell with eight electrons octet rule .The reactivity trend of halogens is influenced by their atomic size and effective nuclear charge. As we move down the group from fluorine to astatine, the atomic size increases due to the addition of electron shells. This increase in atomic size leads to a decrease in the effective nuclear charge experienced by the outermost electrons, as they are further away from the nucleus and are shielded by inner electrons.As a result, the ability of halogens to attract and gain an electron electron affinity decreases down the group. Fluorine, being the smallest halogen with the highest effective nuclear charge, has the highest electron affinity and is the most reactive. Conversely, astatine, being the largest halogen with the lowest effective nuclear charge, has the lowest electron affinity and is the least reactive.In summary, the reactivity trend for halogens in terms of their electronic configuration is as follows:F > Cl > Br > I > AtThis trend indicates that the reactivity of halogens decreases as we move down the group, and this is directly related to their decreasing ability to gain electrons due to the increase in atomic size and decrease in effective nuclear charge.