Hydrogen
Hydrogen is the first element in the periodic table and the first element in Group 1 of the table. It has an atomic number of 1, an atomic mass of 1.00794, and a chemical symbol of H.
Properties
Hydrogen is a colorless, odorless, tasteless gas with a density of 0.08999 grams per liter. By comparison, a liter of air weighs 1.29 grams, 14 times as much as a liter of hydrogen. Hydrogen's boiling point is -422.99°F (-252.77°C) and its freezing point is -434.6°F (-259.2°C). It is slightly soluble in water, alcohol, and a few other common liquids.
Hydrogen is relatively inactive at room temperature, but at elevated temperatures it reacts vigorously with many elements, include oxygen, sulfur, phosphorus, and the halogens. The reaction between hydrogen and oxygen results in the formation of water: 2H2 + O2 2H2O.
Occurrence and Extraction
Hydrogen is the most abundant element in the universe. Nearly nine out of every ten atoms in the universe are hydrogen atoms. In space, hydrogen occurs in two forms, in stars and in the "empty" space between stars. In stars, hydrogen is the raw material used for the nuclear reactions by which stars make their energy. In the interstellar medium, hydrogen atoms occur at a very low density and very low temperature.
Hydrogen is also common on the Earth. It is present in the atmosphere, hydrosphere, and lithosphere in the form of water and other compounds and is the third most abundant element on the Earth after oxygen and silicon. About 15% of all the atoms found on Earth are hydrogen atoms.
Three isotopes of hydrogen exist, hydrogen-1, hydrogen-2, and hydrogen-3. The three isotopes are sometimes known by the names of protium, deuterium, and tritium. Protium is by far the most common of the isotopes, making up about 99.9488% of all hydrogen in nature. Deuterium makes up an additional 0.0156%, while tritium accounts for the final small fraction of the hydrogen found naturally. Tritium is a radioactive element that decays by the loss of a beta particle to become a helium-3 isotope. The isotopes of hydrogen are of considerable research interest because their mass differences are so large. That is, deuterium has twice the atomic mass of protium, and tritium has three times the atomic mass of protium. Such mass differences are most unusual among other sets of isotopes.
The simplest way to prepare hydrogen is by electrolyzing water: 2H2O --electric current: 2H2 + O2. The cost of electricity is too high to make this process commercially feasible, however, and the element is usually prepared by some other method, such as the reaction between hot charcoal and steam: H2O + C CO + H2, or by the reaction between steam and hot methane: H2O + CH4 CO + 3H2, or by the reaction between carbon monoxide and steam: CO + H2O --heat CO2 + H2.
Discovery and Naming
Hydrogen was probably "discovered" many times by early chemists, although none recognized the significance of his discovery. In 1671, for example, the English chemist Robert Boyle described experiments in which he added iron to hydrochloric acid (HCl) and to sulfuric acid (H2SO4) and got a gas that burned easily with a pale blue flame. The gas was obviously hydrogen.
The first person to appreciate the meaning of such experiments was the English chemist and physicist Henry Cavendish. Cavendish, like his predecessors, obtained a flammable gas when he added iron to acids, but he recognized the gas as a new element. The element was named not by Cavendish but by Antoine-Laurent Lavoisier, sometimes called the father of modern chemistry. Lavoisier suggested the name hydrogen after the Greek words meaning "water former."
Uses
The most important use for elemental hydrogen is in the production of ammonia (NH3). Ammonia is made by combining hydrogen and nitrogen under high pressure and high temperature in the presence of a suitable catalyst. The reaction is known as the Haber-Bosch process after the two German scientists who developed it, Fritz Haber and Karl Bosch. The primary use of ammonia, in turn, is in the manufacture of synthetic fertilizers.
Hydrogen is also the starting point in the synthesis of other essential compounds. For example, it can be combined with carbon monoxide to produce methanol (methyl alcohol; CH3OH) which, like ammonia, is used as a raw material in the production of many other important industrial compounds. Another use of hydrogen is in the manufacture of pure metals. Hydrogen gas is passed over hot metal oxides, reducing the oxide to the pure metal. For example: MoO2 + 2H2 --heat 2H2O + Mo.
Hydrogen is also used by the food products industry to convert liquid oils to solid fats in a process known as hydrogenation. The purpose of the reaction is to convert oils into a form that makes them easier to pack and transport. Hydrogen is also used in oxyhydrogen and atomic hydrogen torches that produce flames with temperatures of a few thousand degrees. Such torches are used to cut through metals and to weld two metals to each other.
A once-important use of hydrogen is in lighter-than-air craft, such as dirigibles. This use was largely abandoned because of the dangers in handling gaseous hydrogen. The gas catches fire or explodes relatively easy, a property that led to some horrible airship disasters in the past. Improved methods of handling hydrogen may make it possible for this use to become important once more in the future.
Some people think that hydrogen may be the "fuel of the future." As the world's supplies of fossil fuels diminish, some other fuel will have to be found to take their place. Hydrogen could be that fuel. It burns with a very hot flame, producing only water as a waste product. Imaginative inventors foresee buildings being heated by hydrogen stoves, cars being driven by hydrogen engines, and industrial operations being powered by hydrogen furnaces. The primary factor preventing the "hydrogen economy" from becoming a reality is the high cost of producing pure hydrogen gas in the first place. If and when that problem is solved, service stations of the future may be dispensing hydrogen gas rather than gasoline to keep the nation's economy on the move.
Millions of hydrogen compounds are known. In fact, hydrogen forms more different compounds than any other element. For example, nearly all organic and biochemical compounds containing hydrogen. One of the most important groups of hydrogen compounds is the acids. Each year, acids rank near the top of the list of the top 10 chemicals produced in the United States. Among the most important industrial acids are hydrochloric acid (HCl), sulfuric acid (H2SO4), nitric acid (HNO3), phosphoric acid (H3PO4), acetic acid (HC2H3O4 ), and hydrofluoric acid (HF). These acids are used directly for cleaning metals and other purposes as well as being used as the first step in many different synthetic chemical reactions.
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