Essential Hydrogen Facts
Element Symbol: H
Element Number: 1
Element Category: nonmetal
Atomic Weight: 1.00794(7)
Electron Configuration: 1s1
Discovery: Cavendish, 1766. Hydrogen was prepared for many years before it was recognized as a distinct element.
Word Origin: Greek: hydro meaning water; genes meaning forming. The element was named by Lavoisier.
Hydrogen Physical Properties
Density: 0.89888 g/L (0°C, 101.325 kPa)
Melting Point: 14.01 K, -259.14 °C, -423.45 °F
Boiling Point: 20.28 K, -252.87 °C, -423.17 °F
Triple Point: 13.8033 K (-259°C), 7.042 kPa
Critical Point: 32.97 K, 1.293 MPa
Heat of Fusion: (H2) 0.117 kJ·mol−1
Heat of Vaporization: (H2) 0.904 kJ·mol−1
Molar Heat Capacity: (H2) 28.836 J·mol−1·K−1
Ground Level: 2S1/2
Ionization Potential: 13.5984 ev
Additional Hydrogen Properties
Oxidation States: 1, -1
Electronegativity: 2.20 (Pauling scale)
Ionization Energies: 1st: 1312.0 kJ·mol−1
Covalent Radius: 31±5 pm
Van der Waals Radius: 120 pm
Crystal Structure: hexagonal
Magnetic Ordering: diamagnetic
Thermal Conductivity: 0.1805 W·m−1·K−1
Speed of Sound (gas, 27 °C): 1310 m·s−1
CAS Registry Number: 1333-74-0
Protium and deuterium are not radioactive. Tritium, however, decays into helium-3 through beta decay.
More Hydrogen Facts
- Hydrogen is the lightest element. Hydrogen gas is so light and diffusive that uncombined hydrogen can escape from the atmosphere.
- Hydrogen gas is a mixture of two molecular forms, ortho- and para-hydrogen, which differ by the spins of their electrons and nuclei. Normal hydrogen at room temperature consists of 25% para-hydrogen and 75% ortho-hydrogen. The ortho form cannot be prepared in the pure state. The two forms of hydrogen differ in energy, so their physical properties also differ.
- Hydrogen gas is extremely flammable.
- Hydrogen can take a negative charge (H-) or a positive charge (H+) in compounds. Hydrogen compounds are called hydrides.
- Ionized deuterium displays a characteristic reddish or pink glow.