Hydrogen (H)

Colorless gas

Hydrogen is the simplest and most abundant element in the universe, powering stars and forming water, and with a single proton and electron, hydrogen has the lowest atomic mass and exists in three isotopic forms: protium, deuterium, and tritium. Its 1s¹ electron configuration makes it highly versatile, bonding with nearly every other element.

Key metrics

Density8.99e-5g/cm³

Melting point13.99K

Boiling point20.27K

Electronegativity2.2Pauling

Discovery

1766discovered

Discovered by: Henry Cavendish
Reactivity profile: Immensly Flammable
Reactivity: High
Bonding: Covalent

Electron configuration

\textcolor{#ef4444}{1_{s}^{1}}

1s1

Wave function

\psi_{\text{H}}(r) = \frac{1}{\sqrt{\pi a_0^3}} e^{-r/a_0}

Probability density $|\Psi|^2$ across the H valence shell.

Crystal structure

Hexagonal Close-Packed

Lattice constantsa 1.00 · b 1.00 · c 1.63

Cell anglesα 90° · β 90° · γ 120°

Coordination number12

Atoms per cell2

Atomic packing factor0.74

Physical properties

Atomic radius: 53 pm
Ionization energy: 1312 kJ/mol
Electron affinity: 72.8 kJ/mol
Crystal structure: Hexagonal close-packed (hcp)

Oxidation states

+1-1

Acid/base

Can act as acid or base

Strongly acidicStrongly basic

State at 25 °CGas

13.99 K20.271 K298 K

Emission spectrum

4 transitions

380450500550600650700780

VioletBlueGreenYellowRed

410.2nmHδ (Balmer)Violet15%

434.0nmHγ (Balmer)Violet30%

486.1nmHβ (Balmer)Blue60%

656.3nmHα (Balmer)Red100%

Dominant line 656.3 nmRange 410–656 nmTransitions 4