Hydrogen

Properties and Phases:
– Hydrogen is the lightest element, constituting approximately 75% of all normal matter.
– It is colorless, odorless, tasteless, non-toxic, and highly combustible.
– Hydrogen exists in various phases: gaseous, liquid, slush, solid, and metallic hydrogen.
– It burns with oxygen to produce water and forms explosive mixtures with air and chlorine.
– Hydrogen has specific combustion properties like an enthalpy of combustion of -286 kJ/mol and an autoignition temperature of 500°C.

Chemical Reactions and Compounds:
– Hydrogen forms compounds with elements like halogens, oxygen, carbon, and less electronegative elements.
– Hydrogen bonding is crucial for the stability of biological molecules.
– It forms hydrides with more electropositive elements, which can serve as bridging ligands in coordination complexes.
– Protons are central to acid-base reactions, and hydrogen is a critical component of acidic aqueous solutions.

Isotopes and Thermal/Physical Properties:
– Hydrogen has three isotopes: Hydrogen-1 (Protium), Hydrogen-2 (Deuterium), and Hydrogen-3 (Tritium).
– Deuterium is used in chemical experiments and as a neutron moderator, while Tritium is radioactive and used in luminous paint and nuclear fusion.
– The thermal and physical properties of hydrogen vary with temperature and are essential for industrial applications.

History, Discovery, and Applications:
– Hydrogen was discovered in the 17th century and identified as an element in the 18th century.
– It has a history of use in air travel, industrial applications, chemical labeling experiments, and as a clean energy source.
– Hydrogen-powered engines, airships, and various industrial applications have been developed over the years.

Quantum Theory and Cosmic Significance:
– Hydrogen plays a significant role in quantum theory, with its emission spectrum lines and behavior providing insights into atomic structure and chemical bonds.
– It is the most abundant element in the universe, crucial for star formation, nuclear fusion, and interstellar chemistry.
– Hydrogen’s prevalence in various states, from atomic to plasma, and its production methods contribute to its cosmic significance and potential future developments.

Hydrogen (Wikipedia)

This article is about the chemical element. For other uses, see Hydrogen (disambiguation).

Hydrogen is a chemical element; it has symbol H and atomic number 1. It is the lightest element and, at standard conditions, is a gas of diatomic molecules with the formulaH₂, sometimes called dihydrogen, but more commonly called hydrogen gas, molecular hydrogen or simply hydrogen. It is colorless, odorless, non-toxic, and highly combustible. Constituting about 75% of all normal matter, hydrogen is the most abundant chemical element in the universe. Stars, including the Sun, mainly consist of hydrogen in a plasma state, while on Earth, hydrogen is found in water, organic compounds, as dihydrogen, and in other molecular forms. The most common isotope of hydrogen (protium, ¹H) consists of one proton, one electron, and no neutrons.

Hydrogen, ₁H

Purple glow in its plasma state
Hydrogen
Appearance	Colorless gas
Standard atomic weightAr°(H)
	[1.00784, 1.00811] 1.0080±0.0002 (abridged)
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 (none) ← 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
Phaseat STP	gas
Melting point	(H2) 13.99 K ​(−259.16 °C, ​−434.49 °F)
Boiling point	(H2) 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, 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 (hP4)
Lattice constants	a = 378.97 pm c = 618.31 pm (at triple point)
Thermal conductivity	0.1805 W/(m⋅K)
Magnetic ordering	diamagnetic
Molar magnetic susceptibility	−3.98×10−6 cm3/mol (298 K)
Speed of sound	1310 m/s (gas, 27 °C)
CAS Number	12385-13-6 1333-74-0 (H2)
History
Discovery	Henry Cavendish (1766)
Named by	Louis-Bernard Guyton de Morveau Antoine Lavoisier (1787)
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

In the early universe, the formation of hydrogen's protons occurred in the first second after the Big Bang; neutral hydrogen atoms only formed about 370,000 years later during the recombination epoch as the universe cooled and plasma had cooled enough for electrons to remain bound to protons. Hydrogen, typically nonmetallic except under extreme pressure, readily forms covalent bonds with most nonmetals, contributing to the formation of compounds like water and various organic substances. Its role is crucial in acid-base reactions, which mainly involve proton exchange among soluble molecules. In ionic compounds, hydrogen can take the form of either a negatively charged anion, where it is known as hydride, or as a positively charged cation, H⁺. The cation, usually just a proton (symbol p), exhibits specific behavior in aqueous solutions and in ionic compounds involves screening of its electric charge by surrounding polar molecules or anions. Hydrogen's unique position as the only neutral atom for which the Schrödinger equation can be directly solved, has significantly contributed to the foundational principles of quantum mechanics through the exploration of its energetics and chemical bonding.

Hydrogen gas was first produced artificially in the early 16th century by reacting acids with metals. Henry Cavendish, in 1766–81, identified hydrogen gas as a distinct substance and discovered its property of producing water when burned; hence its name means "water-former" in Greek.

Most hydrogen production occurs through steam reforming of natural gas; a smaller portion comes from energy-intensive methods such as the electrolysis of water. Its main industrial uses include fossil fuel processing, such as hydrocracking, and ammonia production, with emerging uses in fuel cells for electricity generation and as a heat source. When used in fuel cells, hydrogen's only emission at point of use is water vapor, though combustion can produce nitrogen oxides. Hydrogen's interaction with metals may cause embrittlement.