Final answer:
Nitrogen is diamagnetic due to the lack of unpaired electrons, while oxygen is paramagnetic because it has two unpaired electrons in its molecular orbitals, providing a net magnetic moment that attracts it to a magnetic field.
Step-by-step explanation:
The magnetic properties of a molecule can be explained by its electronic structure and molecular orbital theory. Nitrogen (N₂) is diamagnetic because it has no unpaired electrons in its molecular orbitals. All electrons in N₂ are paired, resulting in no net magnetic moment, and thus it is not attracted to a magnet. In contrast, oxygen (O₂) is paramagnetic because there are two unpaired electrons in its antibonding (1₂py, 1₂pzz)* molecular orbitals. This electronic configuration gives oxygen a net magnetic moment, causing it to be attracted to a magnetic field, as seen when liquid oxygen is poured in the vicinity of a magnet. The presence of these unpaired electrons is not predicted by the Lewis structure, which shows a misleading picture of all paired electrons. Molecular orbital theory provides the correct explanation for the paramagnetic nature of O₂.