The short answer to "does H2 have hydrogen bonding" is no. Molecular hydrogen, H2, exists as a pair of hydrogen atoms bound together by a covalent bond. Because the molecule is symmetrical and the electrons are shared equally between the identical atoms, there is no significant separation of charge, or dipole moment, required for hydrogen bonding to occur.
Understanding the Prerequisites for Hydrogen Bonding
To answer whether H2 participates in hydrogen bonding, you must first understand what makes this interaction possible. Hydrogen bonding is not a true chemical bond like the covalent bond holding the H2 molecule together; it is a strong type of dipole-dipole attraction. For this force to happen, a molecule must contain a hydrogen atom bonded directly to a highly electronegative atom like nitrogen (N), oxygen (O), or fluorine (F). These atoms pull electron density away from the hydrogen, creating a significant partial positive charge (δ+) on the hydrogen and a partial negative charge (δ-) on the electronegative atom.
Why H2 Lacks a Dipole Moment
Looking at the structure of H2, you see two hydrogen atoms sharing a pair of electrons. Since both atoms are identical, they have the exact same electronegativity. This means the electrons are pulled equally, resulting in a perfectly nonpolar molecule. Without a permanent dipole, there is no positive end to attract the negative end of another molecule, which is the fundamental mechanism of hydrogen bonding. The molecule simply lacks the necessary polarity.
The Role of Electronegativity
Electronegativity is the driving factor behind the creation of a dipole. In water (H2O), oxygen is far more electronegative than hydrogen, creating a strong dipole. In hydrogen fluoride (HF), the difference is even greater. Because the two atoms in H2 are the same, the electronegativity difference is zero. This zero difference is the definitive reason why H2 does not have the internal charge separation needed to act as a hydrogen bond donor or acceptor.
Comparing H2 to Hydrogen Bonding Molecules
Imagine placing H2 next to water. The water molecule has a strong δ+ hydrogen that reaches out to the δ- oxygen of another water molecule. The H2 molecule, being nonpolar, cannot participate in this dance. It cannot donate a partial positive hydrogen, nor can it accept a hydrogen bond via its electrons. This distinction is crucial for understanding molecular interactions in different substances, from the boiling point of water to the structure of DNA.
Intermolecular Forces in Hydrogen Gas
So if hydrogen bonding is off the table, what holds H2 molecules together in the gas phase? The answer lies in much weaker forces. The primary intermolecular force in H2 is the London dispersion force, which is present in all molecules but is the only significant force in nonpolar gases. These forces are very weak, which explains why hydrogen gas has such a low boiling point of -252.87°C (-423.17°F), requiring extreme cold to liquefy it.
Conclusion on Molecular Hydrogen
While the hydrogen atom is the central player in hydrogen bonding, not every molecule containing hydrogen can engage in this interaction. H2 is a fundamental example of a molecule that lacks the structural requirements. Its symmetrical, nonpolar nature means it relies solely on weak dispersion forces, making it a poor candidate for the strong directional interactions seen in water, alcohols, or acids.
