Similarly, in the second case, there is only one possible spin state, χ χ 0 , 0 , and so this state is commonly referred to as a singlet. We can also observe that the probability amplitude is higher when electrons are close to each other, which means that it is slightly more likely that the electrons will be observed together. This phenomenon is referred to as Fermi heap, and plays an important role in chemical bonding by allowing both electrons to be localized in the internuclear region and thus shielding the positively charged nuclei from electrostatic repulsion with one another.