Hydrogen

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Hydrogen is the lightest chemical element (symbol H) with an atomic number of 1 and atomic weight of 1.00794. Molecular hydrogen (H2) is a colourless, odourless and flammable gas at room temperature.

 

General
Name, symbol, number hydrogen, H, 1
Chemical series nonmetals
Group, period, block 1, 1, s
Appearance colorless
Standard atomic weight 1.00794(7)g·mol-1
Electron configuration 1s1
Electrons per shell 1
Physical properties
Phase gas
Density (0 °C, 101.325 kPa)
0.08988 g/L
Melting point 14.01 K
(−259.14 °C, −434.45 °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
Heat capacity (25 °C) (H2)
28.836 J·mol-1·K-1
Vapor pressure
P/Pa 1 10 100 1 k 10 k 100 k
at T/K         15 20
Atomic properties
Crystal structure hexagonal
Oxidation states 1, -1
(amphoteric oxide)
Electronegativity 2.20 (Pauling scale)
Ionization energies 1st: 1312.0 kJ·mol-1
Atomic radius 25 pm
Atomic radius (calc.) 53 pm
Covalent radius 37 pm
Van der Waals radius 120 pm
Miscellaneous
Thermal conductivity (300 K) 180.5 m W·m-1·K-1
Speed of sound (gas, 27 °C) 1310 m/s
CAS registry number 1333-74-0

 

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