Hydrogen is the first element on the periodic table. This is a fact sheet for the element hydrogen, including its characteristics and physical properties, uses, sources and other data.
Essential Hydrogen Facts
Todd Helmenstine
Element Name: Hydrogen
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.
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
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Phase (@STP): gas
Color: colorless
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
Color: colorless
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
Specific Heat: 14.304 J/g•K
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
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
Hydrogen Sources
Wolfgang Beyer
Free elemental hydrogen is found in volcanic gases and some natural gases. Hydrogen is prepared by decomposition of hydrocarbons with heat, action of sodium hydroxide or potassium hydroxide on aluminum electrolysis of water, steam on heated carbon, or displacement from acids by metals.
Hydrogen Abundance
Hubble Space Telescope, photo PR96-27B
Hydrogen is the most abundant element in the universe. The heavier elements formed from hydrogen or from other elements that were made from hydrogen. Although approximately 75% of the universe's elemental mass is hydrogen, the element is relatively rare on Earth.
Hydrogen Uses
Photo courtesy of National Nuclear Security Administration / Nevada Site Office
Commercially, most hydrogen is used to process fossil fuels and synthesize ammonia. Hydrogen is used in welding, hydrogenation of fats and oils, methanol production, hydrodealkylation, hydrocracking, and hydrodesulfurization. It is used to prepare rocket fuel, fill balloons, make fuel cells, make hydrochloric acid, and reduce metal ores. Hydrogen is important in the proton-proton reaction and carbon-nitrogen cycle. Liquid hydrogen is used in cryogenics and superconductivity. Deuterium is used as a tracer and a moderator to slow neutrons. Tritium is used in the hydrogen (fusion) bomb. Tritium is also used in luminous paints and as a tracer.
Hydrogen Isotopes
Blacklemon67, Wikipedia Commons
The three naturally occurring isotopes of hydrogen have their own names: protium (0 neutrons), deuterium (1 neutron), and tritium (2 neutrons). In fact, hydrogen is the only element with names for its common isotopes. Protium is the most abundant hydrogen isotope. 4H to 7H are extremely unstable isotopes that have been made in the lab but are not seen in nature.
Protium and deuterium are not radioactive. Tritium, however, decays into helium-3 through beta decay.
More Hydrogen Facts
Benji9072
- 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.
