Hydrogen, like the alkali metals (Group 1A) immediately below it in the periodic table, has one electron in its outer shell. Unlike the alkali metals, however, hydrogen has only one electron shell.

Hydrogen (H), the first element of the periodic table, is a tasteless, odorless, colorless gas and the most abundant element in the universe. The sun and many other stars consist mainly of hydrogen, but on earth, where it is only ninth in abundance, most hydrogen is combined with oxygen in water and with carbon in animal and vegetable matter, coal, and petroleum. Its atom consists of a single proton and one electron, so hydrogen has an atomic number of 1.

Hydrogen was first distinguished from other inflammable gases in 1766 by the British chemist Henry Cavendish (1753-1801). The formation of water by burning the gas was observed in 1776. The name hydrogen (from the Greek hydro and genes, meaning “water former’! was proposed in 1781 by the French chemist Antoine Lavoisier (1743-1794). Its atomic number is 1, and its atomic mass is 1.0079. Its melting point is -259.14° C, and its boiling point, -252.87° C. Its isotopes are pro-tium (relative abundance 99.98%), deuterium, and tritium.


In its most common form, hydrogen is a gas. Because it is so light, weighing less than one-tenth as much as an equal volume of air, it was once used to fill balloons and airships. However, hydrogen is also highly flammable, so noninflammable helium, the next lightest element, is used today. Hydrogen is only slightly soluble in water, and while it cannot support life, it is not toxic.

Hydrogen can be condensed to the liquid state at -259.14° Q In this form it is used with liquid oxygen as fuel for rocket engines, such as the main engines of NASA’s Space Shuttle.

Compounds and uses

Hydrogen forms many compounds. It is a component of water and an essential ingredient of acid solutions and bases. It forms organic compounds by combining with carbon and other elements in plant and animal tissue. About half of the hydrogen produced industrially is converted to ammonia, which is oxidized to nitrogen oxide for making the nitric acid used in fertilizers and explosives. Hydrogen is used to produce a simple alcohol called methanol, a basic ingredient in fuels, rubbing compounds, and solvents. It is also used in refineries to upgrade fuel oil to gasoline.

Together with carbon, hydrogen forms a wide variety of hydrocarbons. These compounds, including petroleum and natural gas, provide energy for cooking, heating, generating electrical power, and operating many kinds of machinery. In addition, they are the raw materials used to make many different kinds of plastics and pharmaceuticals. Hydrogen is also used to convert coal to synthetic oil and gas, and hydrogen is added to liquid fats to form solid fats, such as margarine and shortening.


Hydrogen has three isotopes: (1) protium, the most common isotope, with a single proton in the atomic nucleus; (2) deuterium, or heavy hydrogen, with one proton and one neutron; and (3) tritium, the radioactive isotope, with one proton and two neutrons.

Deuterium was discovered in 1932 by the American physicist Harold Urey (1893-1981). Its atomic number is 1, and its atomic mass is 2.01410. Its melting point is -254.4° C, and its boiling point, -249.5° C. It has a relative abundance of 0.0149%, and it is made by electrolysis of heavy water.

The Hindenburg, a hydro-gen-filled airship 804 feet (245 meters) long, burst into flames on approaching the mooring mast at Lakehurst, New Jersey, on May 6,1937. As a result of this still unexplained disaster, interest in airships waned. Recently, however, it has revived and several experimental airships have been built These modern craft are filled with helium, which is not inflammable.

Tritium was discovered in 1934 by the British physicist Ernest Rutherford (1871-1937) and the Australian physicist Marcus Oliphant (1901- ). Its atomic number is 1, and its atomic mass is 3.022. Its melting point is -252.5° C, and its boiling point, -248.1° C. It has a relative abundance of less than .005%, and it is radioactive (half-life 12.26 years).

In a fusion reaction deft),
nuclei of deuterium and tritium fuse. This produces a helium nucleus, a free neutron, and a large amount of energy. Scientists are trying to develop fusion reactors in which the energy of fusion can be controlled and used to generate electricity.

Heavy water, a compound of deuterium and oxygen, is used in some nuclear reactors to help control the fission reaction. If scientists ever succeed in finding a way to control nuclear fusion, the deuterium in heavy water will become the world’s cheapest and most abundant source of energy. Tritium is used in the hydrogen bomb, along with deuterium.

Liquid hydrogen has been used as a propellant for several spacecraft These have included the second and third stages of the Saturn V rocket, used to launch the historic Apollo 11 mission that landed the first humans on the moon.
In such propulsion systems, the liquid hydrogen is reacted with liquid oxygen, producing water (in the form of steam)—and a powerful thrust