by John Traveler

Created on: September 02, 2008   Last Updated: November 21, 2011

Hydrogen is perhaps the most interesting of the elements in the universe, if not its simplest and most abundant one. Atoms of hydrogen represent about 75 percent of all the matter in the cosmos, and even the Earth's crust contains more hydrogen than it does anything else. In fact, with the exception of Helium, all of the other elements in the universe have been formed from hydrogen atoms through a process which takes place in stars called fusion.

Hydrogen is an element with some very unusual and in some cases even exotic properties. It is also the most reactive of elements forming compounds with many other elements.

Chemical Properties

Hydrogen is the simplest element having an atomic number of 1 and its most common isotope has a mass number of 1 also. No other element boasts the same atomic number and mass number. Common hydrogen is unique in that it contains no neutrons, just a single proton in its nucleus and a single electron in orbit round it. Elemental hydrogen is bivalent, meaning that it can either accept or give up an electron in chemical reactions. Besides the common form of hydrogen, there are two isotopes, deuterium and tritium.

Physical Properties

Hydrogen is a gas which can be liquefied only under great pressure and at very cold temperatures. It is also a gas which has some unique properties when highly energized, forming a plasma which has a few unique properties of its own. In chemical reactions hydrogen can donate or accept an electron. Hydrogen even reacts with itself to form a diatomic molecule, and it is in this diatomic state that most hydrogen on earth is found. An example of this is water which consists of an oxygen atom and two hydrogen atoms. In the formation of compounds of hydrogen, substantial energy is dissipated. The combination of hydrogen and oxygen to form water is so vigorous that an enormous amount of energy is liberated and the reaction occurs explosively. This reaction is used to power rocket engines and it is also the primary source of energy in internal combustion engines. The octane rating of gasoline is essentially a measure of the amount of hydrogen it contains.

Hydrogen is lighter than air and in the past has been used in dirigibles and balloons, but its flammability presents a major drawback. Hydrogen is so light that the Earth's gravity is not immense enough to hold on to it and when it rises to the top of the atmosphere it is swept away by the solar winds.

Biological Properties

Hydrogen has a very unusual property

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