Substances like nitrogen and oxygen exist as diatomic molecules (N2 and O2) in their gaseous forms due to the instability of monoatomic species. Monoatomic nitrogen (N) and oxygen (O) are not stable because they need to fill their valence electron shells to achieve a noble gas configuration. This stability is achieved by forming bonds with other atoms, resulting in diatomic molecules. For example, sodium is rarely found as a monoatomic ion (Na+) because it is highly reactive and seeks to bond with other elements, such as in sodium chloride (NaCl). The discussion emphasizes the importance of electron configuration in determining the state and stability of elements.
