1.01This page contains a brief profile and picture of hydrogen, an element which is in many ways its own family. More information can be found via the WWW links following the background sketch on the element. However, as these links are to other servers on the Internet you will need to use the BACK button on your browser to return to this page. Credits for the photos and principal links can be found at the end of this document.
The name hydrogen is taken from the Greek hydro + genes, or "water generator". The gas is colorless, odorless and tasteless and is the most abundant element in the known universe. It is also the lightest (in terms of atomic mass) and the simplest, having only one proton and one electron (and no neutrons in its most common isotope).
First isolated and identified as an element by Cavendish in 1766, hydrogen was believed to be many different things. Cavendish himself thought that it was "inflammable air from metals", owing to its production by the action of acids on metals. Others thought it was pure phlogiston because of its flammability. Hydrogen is among the ten most abundant elements on the planet, but very little is found in elemental form due to its low density and reactivity. Much of the terrestrial hydrogen is locked up in water molecules and organic compounds like hydrocarbons.
The vast majority of hydrogen produced industrially today is made either from treatment of methane gas with steam or in the production of "water gas" from the reaction of coal with steam. Most of this hydrogen is used in the Haber process to manufacture ammonia. The element is also used for hydrogenating vegetable oils, turning them into margarine and shortening, and some is used for liquid rocket fuel.
There are two important isotopes of hydrogen. Deuterium (2H) has an abundance of 0.015% of terrestrial hydrogen and the nucleus of the isotope contains one neutron. Sometimes called heavy hydrogen, deuterium is separated by the fractional distillation of liquid hydrogen but it can also be produced by the prolonged electrolysis of ordinary water. Approximately 100,000 gallons of water will produce a single gallon of D2O, "heavy water". This special kind of water is used as a moderator in some fission power reactors. Deuterium fuel is used in experimental fusion reactors.
Tritium (3H) contains two neutrons in its nucleus and is radioactive. It is very rare (about 1 in every 1018 atoms) and is formed in the environment by cosmic ray bombardment. Most tritium is manufactured by bombarding Li with neutrons. Tritium is used in thermonuclear weapons and experimental fusion reactors.More background information on H More data on H
Elemental iodine is a dark grey solid with a faint metallic luster. When heated at ordinary air pressures it sublimes to a violet gas. The name iodine is taken from the Greek ioeides which means "violet colored". It was discovered in 1811 by Courtois.
Commercially iodine is recovered from seaweed and brines. It is an important trace element in the human diet, required for proper function of the thyroid gland. Thus iodine is added to table salt ("iodized") to insure against iodine deficiencies. Radioactive isotopes of iodine are used in medical tracer work involving the thyroid and also to treat diseases of that gland.More background information on I More data on I
At no images of Astatine available
Astatine is the last of the known halogens and was synthesized in 1940 by Corson and others at the University of California. It is radioactive and its name, from the Greek astatos, means "unstable". The element can be produced by bombarding targets made of bismuth-209 with high energy alpha particles (helium nuclei). Astatine 211 is the product and has a half-life of 7.2 hours. The most stable isotope of astatine is 210 which has a half-life of 8.1 hours.
Not much is known about the chemical properties of astatine but it is expected to react like the other halogens, although much less vigorously, and it should be more metallic than iodine. There should be tiny quantities of astatine in the earth's crust as products of other radioactive decays, but their existence would be short-lived.More background information on At More data on At
Sources: Photos of the elements were taken from the LIFE Science Library book Matter. Background links go to the Periodic Table created at Los Alamos National Laboratories by Robert Husted. Data links go to the primary site of Mark Winter's WebElements, version 2.0, at the University of Sheffield in the United Kingdom.