Astatine (At) is a member of Group 17 (or Group VIIA) of the periodic table, also known as the halogens. The number of valence electrons for elements in Group 17 is typically given by the equation "8 - Group Number." However, astatine is an exception to this trend because it is located in the seventh period.
Astatine is located below iodine (I) in Group 17, and iodine has seven valence electrons. Therefore, astatine is expected to have one additional valence electron compared to iodine, making it likely to have eight valence electrons.
However, it is important to note that astatine is a highly radioactive and extremely rare element, with only trace amounts occurring naturally. Due to its scarcity and radioactivity, its properties are not extensively studied, and experimental data on its electron configuration and valence electrons are limited. Therefore, while it is predicted to have eight valence electrons based on its position in the periodic table, further experimental research is necessary to confirm this value.