Hydrogen
diatomic nonmetal · period 1 · group 1 (alkali metals (and hydrogen)) · s-block
Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element.
What the numbers say
At standard temperature and pressure Hydrogen is a gas, sitting in period 1, group 1 of the s-block.
Its melting point of 14 K (-259 °C) is the 109th highest of the 110 elements with a measured value — among the lowest-melting elements.
At 0 g/cm³ it is the 96th densest of 96 elements with a quoted density.
Pauling electronegativity is 2.2. Paired with oxygen (3.44) that is a difference of 1.24, which puts the bond polar covalent — oxides here tend to be semiconducting or refractory rather than salt-like.
In the solid state it takes a simple hexagonal structure — hexagonal packing offers few easy slip systems, so properties are anisotropic and formability is limited.
It is reported in 2 oxidation states (-1, 1), which sets how many distinct compounds and phases it can form.
First identified in 1766.
Crystal structure
Solid Hydrogen adopts a Simple Hexagonal arrangement, in the Hexagonal system — axes a = b ≠ c, angles α = β = 90°, γ = 120°. Symmetry controls the anisotropy of stiffness and thermal expansion, and the available slip systems set how far the metal deforms before it fractures.
Crystallographic examples
Hydrogen or one of its compounds is a textbook example for this crystal system:
- Triclinic — Kaolinite, albite, CuSO₄·5H₂O
Check it against computed structures
The structure search queries the Materials Project, OQMD and the Open Materials Database for computed crystal structures containing H — with DFT formation energy, hull stability and band gap where the provider publishes them.
K 1
Properties
| Atomic number | 1 |
|---|---|
| Atomic mass | 1.008 u |
| Series | diatomic nonmetal |
| Group | 1 |
| Period | 1 |
| Block | s-block |
| Phase at STP | Gas |
| Density | 0 g/cm³ |
| Melting point | 13.99 K (-259 °C) |
| Boiling point | 20.27 K (-253 °C) |
| Electronegativity (Pauling) | 2.2 |
| Electron configuration | 1s¹ |
| Crystal structure | Simple Hexagonal |
| Oxidation states | -1,1 |
| Discovered | 1766 |
Period 1
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See H in context with all 118 elements.
Working with hydrogen in a real design?
Ask the materials chat how H behaves in your alloy system, what it does to weldability, and which grades to look at — with the source of every number named.