An atom of element with the configuration 1S\(^2\)2S\(^2\)2P\(^6\)3S\(^2\)3P\(^5\) is likely to belong to

Answer Details

The electron configuration 1s² 2s² 2p⁶ 3s² 3p⁵ has a total of 2 + 2 + 6 + 2 + 5 = 17 electrons, which identifies the element as chlorine (Cl, atomic number 17).

The group number of an element in the periodic table is determined by the number of electrons in its outermost (valence) shell. For chlorine, the outermost shell is the third shell (n = 3), which contains:

\[3s^2\,3p^5 = 2 + 5 = 7 \text{ electrons}\]

Therefore, chlorine belongs to Group 7 (also called Group VII or Group 17 in modern IUPAC numbering). Group 7 elements are the halogens: fluorine, chlorine, bromine, iodine, and astatine. They all have seven electrons in their outermost shell, giving them the general outer-shell configuration ns² np⁵.