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About Hydrogen

Hydrogen Bohr

Hydrogen, consisting of one proton and one electron, is the most basic and abundant element in the universe and the third most abundant (next to oxygen and silicon) on planet Earth. In fact, about 15% of all atoms on Earth are hydrogen atoms. Hydrogen is the lightest element, though accounts for roughly 90% of the universe by weight. When hydrogen burns in air, water is left as the only waste product. This element has long been theorized to have the ability of supplanting energy demands in Earth’s current fossil fuel economy. Despite hydrogen’s universal abundance, the easiest method of extraction on Earth is stream reforming of natural gas or through electrolysis of water. To this day, it is still not economically viable to produce hydrogen as an energy source in this manner due to its high input cost and relatively low resultant benefit.

The history of hydrogen’s discovery is a long one, with many ‘discoverers’ suggesting rightful claim. Robert Boyle, an English chemist and physicist, was probably the first to isolate the element in 1671 – though nothing was known about the concept of ‘elements’ at the time. Henry Cavendish, another English chemist and physicist, was able to accurately describe hydrogen’s properties by 1766. But it wasn’t until 1807 when John Dalton wrote about his ‘theory of atoms’ that the concept of ‘distinguishable elements’ was born. In the end, it is Cavendish who is generally credited with the discovery of hydrogen.

Raw hydrogen is primarily employed near the site where it is produced. The two largest uses of hydrogen include fossil fuel processing and ammonia production for fertilizer. Gaseous hydrogen has been used as a basis for lighter-than-air transportation. Many laboratory and common household acids and alcohols are composed of hydrogen compounds. Liquid hydrogen can be used as a superconductor, and when combined with liquid oxygen, is a main component of rocket fuel. Hydrogenation of unsaturated oils produces fats for consumable products. The list of applications that hydrogen touches are innumerable.

Many experts believe that hydrogen forms more compounds than any other element, as it readily attaches to many other elements. To summarize the various compounds with applications in industry and the commercial realm without being exhaustive would be rather incomprehensive. Three isotopes of hydrogen are known to exist, the most common being the single proton of 1H, or protium, which can be considered the essential building block of the universe. The addition to protium of one neutron yields another less common form of 2H, Hydrogen-2, known as deuterium (D). Deuterium is a naturally ocurring component of the earth's oceans; water artificially enriched with deuterium is known as "heavy water." While both protium and deuterium are stable isotopes, 3H (tritium) is radioactive and is often used as a tracer in scientific and industrial systems, in that it can easily be detected when as it gives off radiation. Large quantities of tritium are produced in and for laboratory settings.

Hydrogen Properties

Hydrogen Bohr ModelHydrogen is a Block S, Group 1, Period 1 element. The number of electrons in each of Hydrogen's shells is 1 and its electronic configuration is 1s1. The hydrogen atom has a radius of 37.3.pm and it's Van der Waals radius is 120.pm. In its elemental form, CAS 1333-74-0, hydrogen is a colorless, tasteless, odorless, non-metallic, non-toxic, combustible gas. Hydrogen was discovered by Sir Henry Cavendish in 1766.

Symbol: H
Atomic Number: 1
Atomic Weight: 1.00794
Element Category: nonmetal
Group, Period, Block: 1, 1, s
Color: Colorless
Other Names: Dihydrogen
Melting Point: -259.14 °C, -434.45 °F, 14.01 K
Boiling Point: -252.87 °C, -423.17 °F, 20.28 K
Density: (0 °C, 101.325 kPa 0.08988 g/L
Liquid Density @ Melting Point: 0.07 (0.0763 solid) g·cm3
Density @ 20°C: 0.0000899 g/cm3
Density of Solid: 88 kgµm-3
Specific Heat: N/A
Superconductivity Temperature: N/A
Triple Point: 13.8033 K, 7.041 kPa
Critical Point: 32.938 K, 1.2858 MPa
Heat of Fusion (kJ·mol-1): 0.12
Heat of Vaporization (kJ·mol-1): 0.46
Heat of Atomization (kJ·mol-1): 216.003
Thermal Conductivity: 0.1805 W·m-1·K-1
Thermal Expansion: N/A
Electrical Resistivity: N/A
Tensile Strength: N/A
Molar Heat Capacity: (H2) 28.836 J·mol-1·K-1
Young's Modulus: N/A
Shear Modulus: N/A
Bulk Modulus: N/A
Poisson Ratio: N/A
Mohs Hardness: N/A
Vickers Hardness: N/A
Brinell Hardness: N/A
Speed of Sound: (gas, 27 °C) 1310 m·s-1
Pauling Electronegativity: 2.2
Sanderson Electronegativity: 2.59
Allred Rochow Electronegativity: 2.2
Mulliken-Jaffe Electronegativity: 2.25 (s orbital)
Allen Electronegativity: 2.3
Pauling Electropositivity: 1.8
Reflectivity (%): N/A
Refractive Index: 1.000132 (gas; liquid 1.12) 
Electrons: 1
Protons: 1
Neutrons: 0
Electron Configuration: 1s1
Atomic Radius: N/A
Atomic Radius,
non-bonded (Å):
1.1
Covalent Radius: 31±5 pm
Covalent Radius (Å): 0.32
Van der Waals Radius: 120 pm
Oxidation States: 1, -1 (amphoteric oxide)
Phase: Gas
Crystal Structure: hexagonal
Magnetic Ordering: diamagnetic
Electron Affinity (kJ·mol-1) 72.743
1st Ionization Energy: 1312.0 kJ·mol-1
2nd Ionization Energy: N/A
3rd Ionization Energy: N/A
CAS Number: 1333-74-0
EC Number: 215-605-7
MDL Number: MFCD00070838
Beilstein Number: N/A
SMILES Identifier: [H]
InChI Identifier: InChI=1S/H
InChI Key: YZCKVEUIGOORGS-UHFFFAOYSA-N
PubChem CID: 783
ChemSpider ID: 4515072
Earth - Total: 33 ppm 
Mercury - Total: 0.4 ppm
Venus - Total: 35 ppm
Earth - Seawater (Oceans), ppb by weight: 1.08E+08
Earth - Seawater (Oceans), ppb by atoms: 6.62E+08
Earth -  Crust (Crustal Rocks), ppb by weight: 1500000
Earth -  Crust (Crustal Rocks), ppb by atoms: 31000000
Sun - Total, ppb by weight: 7.5E+08
Sun - Total, ppb by atoms: 9.3E+08
Stream, ppb by weight: 1.15E+08
Stream, ppb by atoms: 1.1E+08
Meterorite (Carbonaceous), ppb by weight: 24000000
Meterorite (Carbonaceous), ppb by atoms: 1.7E+08
Typical Human Body, ppb by weight: 1E+08
Typical Human Body, ppb by atom: 6.2E+08
Universe, ppb by weight: 7.5E+08
Universe, ppb by atom: 9.3E+08
Discovered By: Henry Cavendish
Discovery Date: 1766
First Isolation: N/A

Health, Safety & Transportation Information for Hydrogen

Hydrogen (H) atomic and molecular weight, atomic number and elemental symbolHydrogen is the first and lightest element on the periodic table and the most abundant element in the universe. As a readily refinable gas that is lighter than air, its first uses were in ballooning experiments. It was the gas used by the famous Hindenburg dirigible. It now has numerous industrial applications in oil cracking and production of other non-metallic cations, such as ammonium compounds. Deuterium (2H), an isotope of hydrogen, is used to produce heavy water (2H2O) which has application in nuclear energy production. Hydrogen can easily be generated from renewable energy sources making it a primary focus in the area of alternative energy research. Hydrogen is nonpolluting and forms water as a harmless byproduct during use. The challenges associated with the use of hydrogen as a form of energy include developing safe, compact, reliable, and cost-effective hydrogen storage and delivery technologies.

Hydrogen is highly flammable. Safety data for Hydrogen and its compounds can vary widely depending on the form. For potential hazard information, toxicity, and road, sea and air transportation limitations, such as DOT Hazard Class, DOT Number, EU Number, NFPA Health rating and RTECS Class, please see the safety data tab. The below information applies to elemental (metallic) Hydrogen.

Safety Data
Material Safety Data Sheet MSDS
Signal Word Danger
Hazard Statements H220
Hazard Codes F+
Risk Codes 12
Safety Precautions 9-16-33
RTECS Number MW8900000
Transport Information UN 1049 2.1
WGK Germany nwg
Globally Harmonized System of
Classification and Labelling (GHS)
Flame-Flammables Gas Cylinder - Gases Under Pressure

Hydrogen Isotopes

Hydrogen (H) has three naturally occurring isotopes, 1H, 2H, and 3H.

Nuclide Isotopic Mass Half-Life Mode of Decay Nuclear Spin Magnetic Moment Binding Energy (MeV) Natural Abundance
(% by atom)
1H (protium) 1.00782503207(10) STABLE - 1/2+ 2.7928456 N/A 99.9885
2H (deuterium) 2.0141017778(4) STABLE - 1+ 0.8574376 1.9 0.0115
3H (tritium) 3.0160492777(25) 12.32(2) y β- to 3He 1/2+ 2.97896 8.21 -
4H 4.02781(11) 1.39(10)E-22 s [4.6(9) ] n to 3H 2- N/A 5.29 -
5H 5.03531(11) >9.1E-22 s ? 2n to 3H (1/2+) N/A 6.38 -
6H 6.04494(28) 2.90(70)E-22 s [1.6(4) ] 4n to 2H 2-# N/A 5.52 -
7H 7.05275(108)# 2.3(6)E-23# s [20(5)# ] 4n to 3H 1/2+# N/A 6.33 -
Hydrogen Elemental Symbol (H)

Recent Research & Development for Hydrogen

  • Composite Ni / NiO-Cr2O3 Catalyst for Alkaline Hydrogen Evolution Reaction. Michael K Bates, Qingying Jia, Nagappan Ramaswamy, Robert J Allen, and Sanjeev Mukerjee. J. Phys. Chem. C: February 16, 2015
  • CoSe2 Nanowires Array as a 3D Electrode for Highly Efficient Electrochemical Hydrogen Evolution. Qian Liu, Jinle Shi, Jianming Hu, Abdullah M. Asiri, Yonglan Luo, and Xuping Sun. ACS Appl. Mater. Interfaces: February 13, 2015
  • Catalytically Activated Palladium/Platinum Nanowires for Accelerated Hydrogen Gas Detection. Xiaowei Li, Yu Liu, John C. Hemminger, and Reginald M. Penner. ACS Nano: February 13, 2015
  • Comparative Investigations on Hydrogen Absorption-Desorption Properties of Sm-Mg-Ni Compounds: The Effect of [SmNi5]/[SmMgNi4] Unit Ratio. Qingan Zhang, Ziliang Chen, Yongtao Li, Fang Fang, Dalin Sun, Liuzhang Ouyang, and Min Zhu. J. Phys. Chem. C: February 12, 2015
  • Enhancement of Solar Hydrogen Generation by Synergistic Interaction of La2Ti2O7 Photocatalyst with Plasmonic Gold Nanoparticles and Reduced Graphene Oxide Nanosheets. Fanke Meng, Scott K Cushing, Jiangtian Li, Shimeng Hao, and Nianqiang (Nick) Wu. ACS Catal.: February 12, 2015
  • Hydrogen Release from Ammonia Alane Based Materials: Formation of Cyclotrialazane and Alazine. Vinh Son Nguyen, Devashis Majumdar, Jerzy Leszczynski, and Minh Tho Nguyen. J. Phys. Chem. C: February 11, 2015
  • Observation of Hydrogen Migration in Cyclohexane under Intense Femtosecond Laser Field. Hua Wu, Shian Zhang, Jian Zhang, Yan Yang, Li Deng, Tianqing Jia, Zu-Geng Wang, and Zhenrong Sun. J. Phys. Chem. A: February 11, 2015
  • Electrocatalytic Hydrogen Production by [Ni(7PPh2NH)2]2+: Removing the Distinction Between Endo- and Exo- Protonation Sites. Houston J. S. Brown, Stefan Wiese, John A. S. Roberts, R. Morris Bullock, and Monte L Helm. ACS Catal.: February 11, 2015
  • Cerium Oxide Modified Nickel as a Non-Noble Metal Catalyst for Selective Decomposition of Hydrous Hydrazine to Hydrogen. Lei He, Binglian Liang, Lin Li, Xiaofeng Yang, Yanqiang Huang, Aiqin Wang, Xiaodong Wang, and Tao Zhang. ACS Catal.: February 9, 2015
  • High-performance a-Si/c-Si heterojunction photoelectrodes for photoelectrochemical oxygen and hydrogen evolution. Hsin-Ping Wang, Ke Sun, Sun Young Noh, Alireza Kargar, Meng-Lin Tsai, Ming-Yi Huang, Deli Wang, and Jr-Hau He. Nano Lett.: February 9, 2015
  • Control of Interpenetration in Two-Dimensional Metal–Organic Frameworks by Modification of Hydrogen Bonding Capability of the Organic Bridging Subunits. Masoumeh Servati-Gargari, Ghodrat Mahmoudi, Stuart R. Batten, Vladimir Stilinovi, Derek Butler, Laurance Beauvais, William Scott Kassel, William G. Dougherty, and Donald VanDerveer. Crystal Growth & Design: February 9, 2015
  • Improving Solar Cell Efficiency through Hydrogen Bonding: A Method for Tuning Active Layer Morphology. Taner Aytun, Leonel Barreda, Amparo Ruiz-Carretero, Jessica A. Lehrman, and Samuel I. Stupp. Chem. Mater.: February 9, 2015
  • Photoelectrochemical Generation of Hydrogen from Water Using a CdSe Quantum Dot-Sensitized Photocathode. T. Purnima A. Ruberu, Yuming Dong, Amit Das, and Richard Eisenberg. ACS Catal.: February 6, 2015