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These two exceptions are chromium (Cr) and copper (Cu).
For Cr: The atomic number of chromium is 24, which means the neutral element has 24 electrons.
The noble gas before chromium is Ar, which accounts for 18 electrons. From 18, start with the next subshells until we have 24 electrons: 4s23d4. Arranging the subshells in order of principal quantum number, the predicted electron configuration for Cr is [Ar] 3d44s2.
For elements 1–36, there are two exceptions to the filling order as predicted from the periodic table. Draw the atomic orbital diagrams for the two exceptions and indicate how many unpaired electrons are present.