1HHydrogen1.008 u
Hydrogen (H)
Hydrogen is a nonmetal with atomic number 1, in period 1 and group 1 of the periodic table. Its atomic mass is 1.008 u and its electron configuration is 1s¹. Gas at 25 °C.
Key facts
| Atomic number | 1 |
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| Atomic mass | 1.008 u |
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| Category | Nonmetal |
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| Period | 1 |
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| Group | 1 |
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| Block | s |
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| Electron configuration | 1s¹ |
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| Electrons per shell | 1 |
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| Electronegativity (Pauling) | 2.2 |
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| Oxidation states | −1, +1common in bold |
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| State at 25 °C | Gas |
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| Melting point | 14.01 K−259.14 °C |
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| Boiling point | 20.28 K−252.87 °C |
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| Density | 0.0899 g/L |
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Atomic properties
| First ionization energy | 13.598 eV |
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| Electron affinity | 72.8 kJ/mol |
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| Atomic radius | 53 pm |
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| Covalent radius | 31 pm |
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| Van der Waals radius | 120 pm |
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| Common ions | H⁺, H⁻ |
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| Protons, neutrons, electrons | 1, 0, 1 |
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Physical and thermal properties
| Molar volume | 11.42 cm³/mol |
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| Heat of fusion | 0.558 kJ/mol |
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| Heat of vaporization | 0.452 kJ/mol |
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| Specific heat | 14300 J/(kg·K) |
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| Thermal conductivity | 0.1805 W/(m·K) |
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| Thermal expansion | --- |
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| Mohs hardness | --- |
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| Young’s modulus | --- |
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| Crystal structure | Hexagonal |
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| Magnetic type | Diamagnetic |
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Identification and history
| CAS number | 1333-74-0 |
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| Latin name | Hydrogenium |
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| Discovered by | Henry Cavendish · 1766 |
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| Named by | Antoine Lavoisier · 1783 |
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Natural isotopes
| Isotope | Mass (u) | Abundance |
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| 1H | 1.007825 | 99.9855 % |
| 2H | 2.014102 | 0.0145 % |
Data checked against PubChem (NIH), IUPAC, the NIST Atomic Spectra Database and the IAEA (NUBASE and AME), the same data you see in the app.
A dash (---) means there is no reliable published measurement. The app never makes one up.
See Hydrogen in the app
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Periodic Table