Hydrogen

Hydrogen, ₁H

Purple glow in its plasma state
Hydrogen
Appearance	Colorless gas
Standard atomic weight Ar°(H)
	[1.00784, 1.00811][1]
Hydrogen in the periodic table
Hydrogen Helium Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson – ↑ H ↓ Li Neutronium ← hydrogen → helium
Atomic number (Z)	1
Group	group 1: hydrogen and alkali metals
Period	period 1
Block	s-block
Electron configuration	1s1
Electrons per shell	1
Physical properties
Phase at STP	gas
Melting point	(H 2) 13.99 K ​(−259.16 °C, ​−434.49 °F)
Boiling point	(H 2) 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)[2]
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	(H 2) 0.117 kJ/mol
Heat of vaporization	(H 2) 0.904 kJ/mol
Molar heat capacity	(H 2) 28.836 J/(mol·K)
Vapor pressure P (Pa) 1 10 100 1 k 10 k 100 k at T (K) 15 20
Atomic properties
Oxidation states	−1, 0, +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
Spectral lines of hydrogen
Other properties
Natural occurrence	primordial
Crystal structure	​hexagonal
Speed of sound	1310 m/s (gas, 27 °C)
Thermal conductivity	0.1805 W/(m⋅K)
Magnetic ordering	diamagnetic[3]
Molar magnetic susceptibility	−3.98×10−6 cm3/mol (298 K)[4]
CAS Number	12385-13-6 1333-74-0 (H 2)
History
Discovery	Henry Cavendish[5][6] (1766)
Named by	Antoine Lavoisier[7] (1783)
Isotopes of hydrogen v e
Main isotopes Decay abun­dance half-life (t1/2) mode pro­duct 1H 99.9855% Preview warning: Infobox H isotopes: Abundance percentage not recognised "na=99.9855%" cat#% stable 2H 0.0145% Preview warning: Infobox H isotopes: Abundance percentage not recognised "na=0.0145%" cat#% stable 3H trace 12.32 y β− 3He
Category: Hydrogen view talk edit | references

Hydrogen is a chemical element at the start of the periodic table. It has the symbol H and atomic number 1. It also has a standard atomic weight of 1.008. This makes it the lightest element in the periodic table. In standard conditions, hydrogen is a diatomic gas with the formula H
2, or dihydrogen.^[8] In this state, hydrogen is also called hydrogen gas or molecular hydrogen. Hydrogen has no color, smell, or taste.^[9] Hydrogen is not toxic and is very combustible.^[8]

Hydrogen is the most common chemical element in the universe. Hydrogen is almost 75% of all normal (baryonic) matter by mass.^[10] Most stars are made of mostly hydrogen. Hydrogen stars are made of hydrogen in a plasma state. On Earth, hydrogen is seen in water and organic compounds. Hydrogen's most common isotope has one proton and no neutrons. This isotope also has one electron orbiting around it.

Hydrogen began to form a second after the Big Bang. These hydrogens did not have any neutrons or electrons. The first neutral hydrogen with an electron would not form until 380,000 years later during the recombination epoch, when the universe was cold enough for hydrogens to attract electrons.^[11]

Hydrogen is usually nonmetallic and can form covalent bonds with most nonmetals. These covalent bonds can create molecules such as water and other organic substances. Hydrogen is the main part of acid–base reactions. These reactions exchange protons in soluble molecules. In ionic compounds, ions can either be anions or cations. Hydrogen anions are negatively charged and are called hydrides. Hydrogen cations are positively charged and are written as H+
. Cations are also called protons (symbol p), because they are only made of a proton and nothing else.

Hydrogen gas was first made artificially in the 1700s. Henry Cavendish identified hydrogen gas as a distinct substance between 1766 and 1781.

Most hydrogen production is from steam reforming natural gas. Hydrogen has many industrial uses. Hydrogen can be used to process fossil fuels, hydrocrack, and produce ammonia.

1. ↑ "Standard Atomic Weights: Hydrogen". CIAAW. 2009.
2. ↑ Wiberg, Egon; Wiberg, Nils; Holleman, Arnold Frederick (2001). Inorganic chemistry. Academic Press. p. 240. ISBN 978-0123526519.
3. ↑ Lide, D. R., ed. (2005). "Magnetic susceptibility of the elements and inorganic compounds". CRC Handbook of Chemistry and Physics (PDF) (86th ed.). Boca Raton (FL): CRC Press. ISBN 978-0-8493-0486-6.
4. ↑ Weast, Robert (1984). CRC, Handbook of Chemistry and Physics. Boca Raton, Florida: Chemical Rubber Company Publishing. pp. E110. ISBN 978-0-8493-0464-4.
5. ↑ "Hydrogen". Van Nostrand's Encyclopedia of Chemistry. Wylie-Interscience. 2005. pp. 797–799. ISBN 978-0-471-61525-5.
6. ↑ Emsley, John (2001). Nature's Building Blocks. Oxford: Oxford University Press. pp. 183–191. ISBN 978-0-19-850341-5.
7. ↑ Stwertka, Albert (1996). A Guide to the Elements. Oxford University Press. pp. 16–21. ISBN 978-0-19-508083-4.
8. ↑ ^{8.0 8.1} PubChem. "Hydrogen". pubchem.ncbi.nlm.nih.gov. Retrieved 2024-05-30.
9. ↑ "Hydrogen | Properties, Uses, & Facts | Britannica". www.britannica.com. 2024-05-05. Retrieved 2024-05-30.
10. ↑ "Origin of the Elements". www2.lbl.gov. Retrieved 2024-05-30.
11. ↑ "Early Universe - NASA Science". science.nasa.gov. Retrieved 2024-05-30.