## Chemistry: The Central Science (13th Edition)

[noble gas] $ns^2(n-1)d^2$ 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 d-subshells involved in the outer shell, so the configurations belong to an B group of elements. - There are 2 s-subshell electrons and 2 d-subshell electrons of the previous shell, meaning there are 4 outer-shell electrons in total. That corresponds to the IVB group. In other words, the generalized electron configuration belongs to the IVB group of elements. 2) The $ns$ subshell is occupied by 2 electrons, so it is completely filled and the electrons are paired. The $(n-1)d$ subshell is occupied by 2 electrons, while it has only 5 orbitals. According to Hund's rule, these 2 electrons would each occupy a different orbitals. So, there are 2 one-electron orbitals and 3 zero-electron orbitals. Therefore, there is 2 unpaired electrons.