Hydrogen, 1H
Appearance | colorless gas
Standard atomic weight Ar, std(H) | [1.00784, 1.00811] conventional: 1.008
Atomic number (Z) | 1
Group | 1: H and alkali metals
Period | period 1
Block | s-block
Element category | Reactive nonmetal
Electron configuration | 1s1
Electrons per shell | 1
Phase at STP | gas
Melting point | (H2) 13.99 K ​(−259.16 °C, ​−434.49 °F)
Boiling point | (H2) 20.271 K ​(−252.879 °C, ​−423.182 °F)
Density (at STP) | 0.08988 g/L
when liquid (at m.p.) | 0.07 g/cm3 (solid: 0.0763 g/cm3)
when liquid (at b.p.) | 0.07099 g/cm3
Triple point | 13.8033 K, ​7.041 kPa
Critical point | 32.938 K, 1.2858 MPa
Heat of fusion | (H2) 0.117 kJ/mol
Heat of vaporization | (H2) 0.904 kJ/mol
Molar heat capacity | (H2) 28.836 J/(mol·K)
Oxidation states | −1, +1 (an amphoteric oxide)
Electronegativity | Pauling scale: 2.20
Ionization energies | 1st: 1312.0 kJ/mol
Covalent radius | 31±5 pm
Van der Waals radius | 120 pm
Natural occurrence | primordial
Speed of sound | 1310 m/s (gas, 27 °C)
Thermal conductivity | 0.1805 W/(m·K)
Magnetic ordering | diamagnetic
Magnetic susceptibility | −3.98·10−6 cm3/mol (298 K)
CAS Number | 12385-13-6 1333-74-0 (H2)
Discovery | Henry Cavendish (1766)
Named by | Antoine Lavoisier (1783)