H2
dihydrogen · molecular hydrogen, hydrogen gas
Dihydrogen is a stable, colorless, and odorless diatomic gas that serves as the primary molecular form of the element hydrogen.
About dihydrogen
Dihydrogen is the simplest diatomic molecule, consisting of two hydrogen atoms covalently bonded together. It exists as a wide-gap insulating gas under standard conditions and is recognized as a thermodynamically stable phase that sits firmly on the convex hull of chemical stability.
Its significance spans from fundamental physics to large-scale industrial applications. As a highly data-rich material with numerous reported structures, it serves as a critical subject for understanding molecular bonding and high-pressure condensed matter physics.
Key Properties
Cross-validated computational properties for dihydrogen, aggregated across 5 databases.
Band GapEnergy needed to move an electron from the valence band to the conduction band. Lower or zero values tend to behave more metallic; larger gaps are more insulating or semiconducting.
Energy Above HullThermodynamic distance from the most stable set of competing phases. 0 eV/atom is on the convex hull; small positive values may still be experimentally accessible.
StabilityA plain-language summary of the best reported energy-above-hull result. It reflects whether the lowest-energy structure is on, near, or far from the stability hull.
StructuresCount of reported calculated crystal structures for this formula, including alternate polymorphs, source databases, and observed space groups.
Reported Structures
Lowest-energy structures reported for H2, ranked by energy above hull.
| Space GroupSymmetry classification of the crystal arrangement. The number is the international space-group index. | Crystal SystemBroad lattice family, such as cubic, tetragonal, monoclinic, or triclinic, derived from unit-cell symmetry. | Band Gap (eV)Electronic gap calculated for this specific reported structure, measured in electronvolts. | E above hull (eV/atom)Thermodynamic distance from the convex hull for this structure, normalized per atom. Lower is generally more stable. | E/atom (eV)Computed total energy normalized per atom. Use energy above hull, not this value alone, when comparing stability. | Density (g/cm³)Mass per relaxed crystal volume, reported in grams per cubic centimeter. |
|---|---|---|---|---|---|
| P212121 (No. 19) | orthorhombic | 9.72 | 0.0000 | -3.455 | 0.04 |
| I4/mmm (No. 139) | tetragonal | 9.33 | 0.0006 | -3.454 | 0.11 |
| Cmce (No. 64) | orthorhombic | 8.80 | 0.0015 | -3.454 | 0.12 |
| I4/mmm (No. 139) | tetragonal | 8.53 | 0.0018 | -3.453 | 0.10 |
| I4/mmm (No. 139) | tetragonal | 10.51 | 0.0019 | -3.453 | 0.10 |
| Pnma (No. 62) | orthorhombic | 8.33 | 0.0023 | -3.453 | 0.08 |
| P63/mmc (No. 194) | hexagonal | 8.07 | 0.0024 | -3.453 | 0.10 |
| P21 (No. 4) | monoclinic | 8.19 | 0.0027 | -3.452 | 0.07 |
| I4/mmm (No. 139) | tetragonal | 8.85 | 0.0030 | -3.452 | 0.14 |
| Pnma (No. 62) | orthorhombic | 7.39 | 0.0035 | -3.452 | 0.13 |
| Cmmm (No. 65) | orthorhombic | 6.23 | 0.0525 | -3.403 | 0.12 |
| P6/mmm (No. 191) | hexagonal | 0.00 | 0.3790 | -3.076 | 0.24 |
Applications
Where dihydrogen is used.
Frequently Asked Questions
Common questions about dihydrogen, answered from cross-validated data.
What is H2?
Dihydrogen is a stable, colorless, and odorless diatomic gas that serves as the primary molecular form of the element hydrogen.
What is H2 used for?
What is the band gap of H2?
Is H2 a metal, semiconductor, or insulator?
Is H2 thermodynamically stable?
What is the crystal structure of H2?
What is the density of H2?
How many polymorphs of H2 are known?
What elements does H2 contain?
Where does the data for H2 come from?
How It Compares
As the fundamental building block of the periodic table, dihydrogen defines the baseline for molecular stability and electronic insulation in gaseous phases, representing the most basic form of chemical bonding.
Data sources & attribution
- materials_project — Data from the Materials Project. Cite: Jain et al., APL Materials 1, 011002 (2013).
- aflow — Data from AFLOW. Cite: Curtarolo et al., Comp. Mater. Sci. 58, 218 (2012).
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