1. The problem statement, all variables and given/known data Our teacher said that if a material has an odd number of electrons, it implies a paramagnetic behavior. Copper, according to him, has odd number of electrons but is considered a diamagnetic material. He asks us to explain this phenomenon. 2. Relevant equations Copper has 29 electrons. And its electron configuration is 1s22s22p63s23p64s13d10 3. The attempt at a solution According to what they (internet) say, the d subshell borrowed an electron from the s subshell on n=3 (see electron configuration). This accounts for the diamagnetism. But isn't it that the electron on the s subshell is unpaired, and should cause the Cu to paramagnetic? Or is it the outermost subshell that is only considered? :( Thanks a lot.