Hydrogen,  ₁H

Purple glow in its plasma state
General properties
Appearance	colorless gas
Standard atomic weight (Ar, standard)	[1.00784, 1.00811]
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 – ← hydrogen → helium
Atomic number (Z)	1
Group	group 1
Period	period 1
Block	s-block
Element category	reactive nonmetal
Electron configuration	1s1
Electrons per shell	1
Physical properties
Phase at STP	H: Gas
Melting point	13.99 K ​(−259.16 °C, ​−434.49 °F)
Boiling point	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)
Vapor pressure P (Pa) 1 10 100 1 k 10 k 100 k at T (K) 15 20
Atomic properties
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
Spectral lines of hydrogen
Other properties
Natural occurrence	H: Primordial
Crystal structure	​hexagonal
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)
History
Discovery	Henry Cavendish (1766)
Named by	Antoine Lavoisier (1783)
Main isotopes of hydrogen
Iso­tope Abun­dance Half-life (1/2) Decay mode Pro­duct 1H 99.98% stable 2H 0.02% stable 3H trace 12.32 y β− 3He
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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, which makes it the lightest element in the periodic table.

Hydrogen is the most common chemical element in the Universe, making up 75% of all normal (baryonic) matter (by mass). Most stars are made of mostly hydrogen. Hydrogen's most common isotope has one proton with one electron orbiting around it.