Beryllium (Be) has zero unpaired electrons in its ground state. Beryllium has an atomic number of 4, giving it an electron configuration of 1s² 2s². Both the 1s and 2s orbitals are completely filled with paired electrons (two electrons per orbital with opposite spins), so there are no unpaired electrons present. When beryllium forms bonds or becomes ionized, the number of unpaired electrons can change. For example, in an excited state, one of the 2s electrons could be promoted to a 2p orbital, creating unpaired electrons. However, in the neutral ground state atom, all electrons are paired. This is why beryllium is diamagnetic—substances with no unpaired electrons are repelled by magnetic fields. The concept of unpaired electrons is important in chemistry because unpaired electrons make atoms paramagnetic (attracted to magnetic fields) and significantly influence how atoms bond and interact with one another.