Zinc has the highest enthalpy of ionization

Name, symbol, atomic number Hydrogen, H, 1
Group, period, block1, 1, s
Look colorless gas
Mass fraction of the earth's envelope 0,88 %
Atomic mass 1.00794 u
Atomic radius (calculated) 25 (53) pm
Covalent radius 37 pm
Van der Waals radius 120 pm
Electron configuration 1s1
Electrons per energy level 1
1. Ionization energy 1312 kJ / mol
Physical state gaseous
Crystal structure none (gas)
density 0.0899 kg m−3 at 273 K
magnetismMagn. Susceptibility = 8 · 10−9
Melting point 14.025 K (−259.125 ° C)
boiling point 20.268 K (−252.882 ° C)
Molar volume 22,42 · 10−3 m3/ mol
Heat of evaporation 0.891 kJ / mol
Heat of fusion 0.117 kJ / mol
Vapor pressure

209 · 103Pa at 23 K

Speed ​​of sound 1314 m / s at 298.15 K.
Specific heat capacity 14304 J / (kg K)
Electric conductivity 0 S / m
Thermal conductivity 0.1815 W / (m K)
Oxidation states +1, −1
Oxides (basicity) H2O, H2O2 (amphoteric)
Normal potential 0
Electronegativity 2.1 (Pauling scale)
NMR properties
  Spinγ in
rad · T−1· S−1
E. fL. at
W = 4.7 T
in MHz
1H 1/2 26,752 1,00 100.0 (2.348 T)
2H1 4,107 1,45 · 10 −615,351 (2,348 T)
safety instructions
Hazardous substance labeling
from RL 67/548 / EEC, Annex I
R and S phrases R: 12
S: (2-) 9-16-33
As far as possible and customary, SI units are used.
Unless otherwise noted, the data given apply to standard conditions.

hydrogen is a chemical element with the symbol H (for Latin hydrogenium "Water generator"; from ancient Greek ὕδωρhydōr "Water" and γίγνομαιgignomai "Become, arise") and the ordinal number 1. In the periodic table it is in the 1st period and the 1st group, so it takes first place.

Hydrogen is the most common chemical element in the universe, but not in the earth's crust. It is part of water and most organic compounds; in particular it occurs in all living organisms.

Hydrogen is the lightest of the chemical elements, the most common isotope consists of only one proton and one electron and is called protium. This comes under the conditions that normally prevail on earth (see also normal conditions) atomic hydrogen instead of hydrogen in the dimerized form, the molecular hydrogen H2, a colorless and odorless gas.


Hydrogen was discovered by the English chemist and physicist Henry Cavendish in 1766 when he was experimenting with mercury and acids. When he brought the two substances together, small gas bubbles formed in the mixture. On closer examination, he could not identify this as one of the known gases. Although he wrongly assumed that hydrogen was part of mercury (instead of part of acid), he was able to describe the properties of the gas well.

A more detailed analysis was done by Antoine Lavoisier. The French chemist discovered the gas independently of Cavendish in 1787 when he wanted to show in an experiment that no mass is lost or generated in chemical reactions. He heated water in a closed apparatus and let the steam condense elsewhere. He found that the mass of the condensed water was slightly less than that of the original amount. A gas was created for this (H.2), the mass of which corresponded exactly to the "lost" amount of water. So his actual experiment was successful.

Lavoisier investigated the resulting gas further and carried out what is now known as the oxyhydrogen test, which burned the gas. He therefore initially called it “combustible air”. When he showed in further experiments that water can also be produced from the gas in reverse, he baptized it as hydro-gène (hydro = water, Greek; genes = generating). The word therefore means: "water builder". The German name suggests the same origin of the term.


Hydrogen is the most common chemical element in the sun and the large gas planets Jupiter, Saturn, Uranus and Neptune, which combine over 99.99% of the mass of the solar system. An even higher proportion of hydrogen is assumed to exist in the entire universe (ignoring dark matter). Hydrogen makes up 75% of the total mass, or 93% of all atoms in the solar system.

Occurrence in the universe

Shortly after the creation of the universe, protons and neutrons were already present in overwhelming numbers. At the prevailing high temperatures, these combined to form light atomic nuclei, such as D and 4Hey Most protons, however, remained unchanged and were the future ones 1H-nuclei. After about 380,000 years, after the radiation density of the universe had become small enough, hydrogen atoms could simply form by merging the nuclei with the electrons without being torn apart again by a photon. Since then there has been (unscattered!) Cosmic background radiation and space is filled with hydrogen.

As the universe continued to cool, the mass split up asymmetrically and formed clouds of hydrogen gas. Under the influence of gravity these increasingly condensed first to form galaxies and later the gas of the galaxies condensed into protostars, and under the enormous pressure of gravity the fusion of the H atoms to form He atoms began. This is how the first stars and suns came into being. Later, especially in very large stars, heavier elements such as carbon, nitrogen and oxygen, which are the basic building blocks of all known forms of life, were also formed - also through fusion.

Stars are mainly made up of hydrogen plasma. The nuclear fusion of hydrogen 1H occurs mainly through the intermediate stages of deuterium2H and tritium3H to helium4Hey The energy released is the energy source of the stars. The hydrogen contained in our sun makes up most of the total mass of our solar system.

But the heavy gas planets also largely consist of hydrogen, which further increases the mass fraction of the element in the solar system. Under the extreme pressures that prevail at great depths in the great gas planets Jupiter and Saturn, it can exist in metallic form. The proportion of metallic hydrogen in the celestial bodies is probably even greater than previously assumed. Because of the electrical conductivity, this state is probably responsible for the formation of the planetary magnetic fields.

Outside of our solar system, hydrogen also occurs in gigantic gas clouds. In the so-called H-I areas, the element is non-ionized and molecular. These areas emit radiation at around 1420 MHz, the 21 cm line that results from transitions in total angular momentum. It plays an important role in astronomy and is used to locate and investigate hydrogen deposits in space.

Ionized gas clouds with atomic hydrogen, on the other hand, are called H-II regions. In these areas, large stars emit large amounts of ionizing radiation. With their help, conclusions can be drawn about the composition of interstellar matter. Due to the constant ionization and recombination of the atoms, they sometimes emit visible radiation that is often so strong that these gas clouds can be seen with a relatively small telescope.

Earthly occurrences

On earth, the mass fraction is much lower, based on the total weight about 0.12%, based on the earth's crust 2.9%. In addition - in contrast to the occurrences in space - the terrestrial hydrogen is mainly bound and almost never pure (i.e. as an unmixed gas). No other element is known to have so many compounds; the most common is water.

Earth crust

The element is also found in all living things, in crude oil, natural gas and in many minerals. Other natural occurrences are natural gases such as methane (CH4).

Salt and fresh water

The largest proportion of earthly hydrogen occurs in the compound water. In this form it covers over two thirds of the earth's surface. The total water resources on earth amount to around 1386 billion km³. Of this, 1338 billion km³ (96.5%) are salt water in the oceans. The remaining 3.5% is fresh water. Most of this is in the solid state: in the form of ice in the Arctic and Antarctic as well as in the permafrost soils v. a. in Siberia. The small remaining portion is liquid fresh water and is mostly found in lakes and rivers, but also in underground deposits, such as groundwater.

the atmosphere