* Valence Electrons: Hydrogen has only one electron in its outermost shell. To achieve a stable configuration, it needs to share one electron to form a single covalent bond.

* Atomic Orbitals: Hydrogen only has one s-orbital, which can hold a maximum of two electrons. It lacks the p-orbitals necessary to form double bonds.

* Octet Rule: Hydrogen only needs two electrons (a duet) to fill its outermost shell, and a single bond satisfies this.

In summary: Hydrogen's limited electron capacity and lack of p-orbitals prevent it from forming double bonds.