One bit of evidence that the quantum mechanical model is "correct" lies in the magnetic properties of matter. Atoms with unpaired electrons are attracted by magnetic fields and thus are said to exhibit paramagnetism. The degree to which this effect is observed is directly related to the number of unpaired electrons present in the atom. Consider the ground-state electron configuration for . Would this atom be expected to be paramagnetic, and how many unpaired electrons are present? It has unpaired electron(s). Consider the ground-state electron configuration for . Would this atom be expected to be paramagnetic, and how many unpaired electrons are present?

For an atom to be paramagnetic, it must possess at least one unpaired electron in its valence shell. Ba and Hg are not paramagnetic because all electrons in their outermost shells are spin paired.

The more the number of unpaired electrons in the outermost shell of an atom, the greater its paramagnetic behavior.