Think of diatomic elements like 'best friends' who are rarely seen alone in nature; they prefer to walk in pairs to maintain stability, whereas noble gases like Helium are the 'independent loners' who are perfectly stable on their own.

Remember 'Have No Fear Of Ice Cold Beer' for the common diatomic elements: Hydrogen ($H_2$), Nitrogen ($N_2$), Fluorine ($F_2$), Oxygen ($O_2$), Iodine ($I_2$), Chlorine ($Cl_2$), and Bromine ($Br_2$).

Diatomic molecules are formed when atoms share electrons to achieve a stable valence shell, typically following the octet rule (or the duet rule for hydrogen). For $H_2$, the single electron from each hydrogen atom is shared to form a single covalent bond, represented by the molecular orbital configuration $(\sigma_{1s})^2$. This lowers the potential energy of the system compared to two isolated hydrogen atoms.

In competitive exams, always distinguish between 'elements' and 'compounds'. A diatomic molecule with two different atoms (like $CO$ or $HCl$) is a compound, not an element.