Hydrogen atom is the simplest atom of all the elements in the periodic table. It is composed of a proton which is confined to the nucleus and an electron which circulates around the nucleus in circular motion. It is the third element in abundance on earth after oxygen and silicon. Its simple structure attracted the attention of physicist as to predict the structure of the atom not known for sure at that time. The Bohr theory of the hydrogen atom was the first successful theory that predicted the structure and energetics of the hydrogen atom. This theory assumed the quantization of the angular momentum.

This theory although was successful to solve the orbital energies for the hydrogen atom was not possible to be applied to other atoms. Schroedinger equation came later and although it can be solved accurately only for the hodrogen atom it could be applied to other atoms or even molecules through the application of perturbation theory. Einestein predicted the formation of the hydrogen bomb based on his observation that the nuclear reaction on the surface of the sun between two hyroden nuclei fusion to give a helium atom releasing a massive amount of energy.

Removal of the only electron in the hydrogen atom by ionization forms a positively charged hydrogen atom which is called a proton because it has only a proton confined to the nucleus. According to the Bronsted theory of acids and bases proton or H+ is an acid and that every molecule which releases a proton is considered as an acid.

Adding an electron to a neutral hydrogen atom forms a reactive species that is called a hydride. All metal bonds to hydrogens are of the hydride type. This is so due to the lower electronegativity of metals in comparison with hydrogen which is more electronegative. Halogens and chalcogens form bonds with hydrogen of the proton types and this is so due the higher electronegativity of the halogens and chalcogens in comparison with hydrogen.

Covalent bonds between atoms and hydrogen do also exist. An example is a bond between the carbon group and hydrogen. Methane is an example of a compound with covalent bond between carbon and hydrogen. This is so due to the similarity in electronegativities between carbon and hydrogen.

Isotops of hydrogen are known in which one neutron exist in the hydrogen nucleus along with the proton. This isotop is called deuterium and forms heavy water or D2O which is the analogue of light water or H2O. D2O is used in nuclear energy processing. It slows down the neutrons stream that bombards Uranium elements. Thus controlling the fision process of the radioactive atom. Another isotop of hydrogen has two neutrons in the nucleus and is called tritium.

The binding of two hydrogen atoms form the hydrogen molecule. The hydrogen molecule is a relatively stable compound that has a covalent bond between the two hydrogen atoms. It can be prepared from a reaction of a hydride source with water such as the following reaction:

NaH + H2O-> H2 + NaOH

It can also be prepared from dissolving of sodium metal in water according to the following equation:

Na + H2O -> H2 + Na2O

Hydrogen molecule can add across a double bond using a catalyst such as palladium or Pd.

Hydrogen bonds are special type of electrostatic interaction that happens for example in a solution of pure water. These bonds in water are responsible for the relatively high boiling temperature of water which is 100 degrees celsius in comparison to 30 degrees celsius in ethers which do not have hydrogen bonds.

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