Chemistry: The Central Science (13th Edition)

[noble gas] $ns^2np^5$ 1) In this type of question, we would look entirely at the outer-shell electrons (the number of outer-shell electrons, the types of subshells, etc.) - Here we notice that there are only s- and p-subshells involved in the outer shell, so the configurations belong to an A group of elements. - There are 2 s-subshell electrons and 5 p-subshell electrons, meaning there are 7 outer-shell electrons in total. That corresponds to the VIIA group. In other words, the generalized electron configuration belongs to the VIIA group of elements. 2) The $ns$ subshell is occupied by 2 electrons, so it is completely filled and the electrons are paired. The $np$ subshell is occupied by 5 electrons, while it has only 3 orbitals. According to Hund's rule, the first 3 electrons would each occupy a different orbital, then the last 2 electrons would each occupy 1 different orbital out of 3. That leaves 1 orbital having only 1 electron. Therefore, there is 1 unpaired electron.