Hydrogen

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– ← hydrogen → helium
–
↑
H
↓
Li
Atomic properties
Atomic number 1
Standard atomic weight 1.007 94(7)
Electron configuration 1s1
Physical properties (H2)[1][2][3]
Melting point 13.957 K (−259.193 °C)
Boiling point 20.39 K (−252.76 °C)
Triple point 13.85 K, 0.072 bar
Critical point 33.18 K, 13.00(1) bar
Density 0.085 kg m−3 (1 atm, 15 °C)
1.312 kg m−3 (1 atm, 20.4 K)
0.070 973 g cm−3 (l, 20.4 K)
Chemical properties[3][4]
Electronegativity 2.20 (Pauling)
Solubility in water 21.4 cm3 kg−1 (1 atm, 0 °C)
Ionization energy[5]
13.598 432 44(36) eV
1305.584 631(12) kJ mol−1
Electron affinity[6]
0.754 209(3) eV
72.7701(3) kJ mol−1
Atomic radii[7][8]
Covalent radius 31 pm
Van der Waals radius 120 pm
Thermodynamic properties (H2)[2][9]
Standard entropy 130.680(3) J K−1 mol−1
Enthalpy change of atomization 217.998(6) kJ mol−1
Entropy change of atomization 114.717(2) J K−1 mol−1
Enthalpy change of vaporization 0.904 kJ mol−1
Hazards[3][10]
GHS pictograms Flam. Gas 1Press. Gas
GHS signal word DANGER
GHS hazard statements H220
Autoignition temperature 560 °C
Miscellaneous
CAS number 1333-74-0
EC number 215-605-7
Where appropriate, and unless otherwise stated, data are given for 100 kPa (1 bar) and 298.15 K (25 °C).
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Hydrogen (symbol: H) is a chemical element, the most abundant element in the universe.

Notes and references

Notes

References

  1. ↑ Hydrogen. In NIST Chemistry WebBook; National Institute for Standards and Technology, <http://webbook.nist.gov/cgi/inchi/InChI%3D1S/H2/h1H>. (accessed 20 June 2010).
  2. ↑ 2.0 2.1 Greenwood, Norman N.; Earnshaw, A. Chemistry of the Elements; Pergamon: Oxford, 1984; pp 38–74. ISBN 0-08-022057-6.
  3. ↑ 3.0 3.1 3.2 Hydrogen. In Gas Encyclopedia; Air Liquide, <http://encyclopedia.airliquide.com/encyclopedia.asp?GasID=36>. (accessed 3 April 2010).
  4. ↑ Allred, A. L. Electronegativity values from thermochemical data. J. Inorg. Nucl. Chem. 1961, 17 (3–4), 215–21. DOI: 10.1016/0022-1902(61)80142-5.
  5. ↑ Moore, Charlotte E. Ionization potentials and ionization limits derived from the analyses of optical spectra. Natl. Stand. Ref. Data Ser., (U.S. Natl. Bur. Stand.) 1970, 34, 1–22, <http://www.nist.gov/data/nsrds/NSRDS-NBS34.pdf>.
  6. ↑ Hotop, H.; Lineberger, W. C. Binding energies in atomic negative ions. II. J. Phys. Chem. Ref. Data 1985, 14 (3), 731–50. DOI: 10.1063/1.555735.
  7. ↑ Cordero, Beatriz; Gómez, Verónica; Platero-Prats, Ana E.; Revés, Marc; Echeverría, Jorge; Cremades, Eduard; Barragán, Flavia; Alvarez, Santiago Covalent radii revisited. Dalton Trans. 2008 (5), 2832–38. DOI: 10.1039/b801115j.
  8. ↑ Bondi, A. van der Waals Volumes and Radii. J. Phys. Chem. 1964, 68 (3), 441–51. DOI: 10.1021/j100785a001.
  9. ↑ Cox, J. D.; Wagman, D. D.; Medvedev, V. A. CODATA Key Values for Thermodynamics; Hemisphere: New York, 1989. ISBN 0891167587, <http://www.codata.org/resources/databases/key1.html>.
  10. ↑ Index no. 001-001-00-9 of Annex VI, Part 3, to Regulation (EC) No 1272/2008 of the European Parliament and of the Council of 16 December 2008 on classification, labelling and packaging of substances and mixtures, amending and repealing Directives 67/548/EEC and 1999/45/EC, and amending Regulation (EC) No 1907/2006. OJEU L353, 31.12.2008, pp 1–1355 at p 340.

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