Chemistry and Chemical Reactivity (9th Edition)

In order to create the noble gas configuration, look for the noble gas that comes before the given element. Then, starting at that element, write the correct electron configuration. a) As, group 15, period 4: $[Ar]\ 3d^{10}\ 4s^2\ 4p^3$. b) Kr, group 18, period 4: $[Ar]\ 3d^{10}\ 4s^2\ 4p^6$