By the periodic table’s logic, all d-block elements should have filled s orbitals. But copper defies that logic. It should have the electron configuration [Ar] 3d 9 4s 2.

Eight deaths later, it is still the only suspect in custody. It is potassium cyanide, a white, odorless substance known to chemists by its nomenclature, KCN. It’s available generally in three… ...