SAT Chemistry

Answer: [Ar] 4s¹3d¹⁰

To write the abbreviated electron configuration for an element, begin with the noble gas in the period directly above that element. Then, account for the s-block, d-block, and p-block valence electrons. Copper has no p-block valence electrons, so in this question one must only consider s-block and d-block electrons. However, copper is one of several elements that allows one electron from the s-orbital to be held in the d-orbital. Thus, the correct electron configuration for copper is [Ar]4s¹3d¹⁰.