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| '''Hydrogen''' is a ] in the ] that has the symbol H and ] 1. A colorless, odorless, ], univalent, highly flammable diatomic gas, hydrogen is the lightest and most abundant element in the ] and is present in ] and in all organic compounds and living organisms. Hydrogen is able to chemically react with most elements. ]s in their ] overwhelmingly composed of hydrogen in its ] state. This element is used as a lifting gas, an alternative fuel, the power-source of ]s | |||
| '''Hydrogen''' is a ] in the ] that has the symbol H and ] 1. | |||
| == Notable Characteristics == | == Notable Characteristics == | ||
| At ] conditions, hydrogen forms a ] ], H |
Hydrogen is the lightest chemical element with its most common isotope consisting of just a single ] and ]. At ] conditions, hydrogen forms a ] ], H<sub>2</sub>, with a boiling point of only 20.27 ] and a melting point of 14.02 K. Under exceedingly high pressures, like those found at the center of ]s, the molecules lose their identity and the hydrogen becomes a liquid ]. Under the exceedingly low pressure conditions found in space, hydrogen tends to exist as individual atoms, simply because there is no way for them to combine; clouds of H<sub>2</sub> form and are associated with ]. | ||
| ⚫ | == Applications == | ||
| ⚫ | Large quantities of hydrogen are needed industrially, notably in the ] for the production of ], the ] of ]s and ]s, and the production of ]. Other |
||
| This element plays a vital role in powering the universe through the ] and ] (these are ] processes that release huge amounts of energy through combining two hydrogen atom into one ]). | |||
| ⚫ | |||
| ⚫ | == Applications == | ||
| ⚫ | Large quantities of hydrogen are needed industrially, notably in the ] for the production of ], the ] of ]s and ]s, and the production of ]. Other uses that require hydrogen; | ||
| *hydrodealkylation, hydrodesulfurization, and hydrocracking. | |||
| *manufacture of ], ], ] ]s, and the reduction of metallic ]s. | |||
| *liquid hydrogen is used in ] research including ] studies, | |||
| *] is produced in ]s and is used in ] construction. | |||
| ⚫ | * It is fourteen and a half times lighter than air and at one time was widely used as a lifting agent in ]s and ]s. | ||
| ⚫ | *] is used in nuclear applications as a moderator to slow down ]s, and deuterium compounds have applications in ] and ] in studies of reaction ]s. | ||
| *Tritium is used as an isotopic label in the biosciences, as a ] source in luminous paints. | |||
| Hydrogen can be burned in ]s, and a fleet of hydrogen burning ]s is maintained by Chrysler-BMW. Hydrogen ]s are being looked into as a way to provide potentially cheap, ]- free ]. | Hydrogen can be burned in ]s, and a fleet of hydrogen burning ]s is maintained by Chrysler-BMW. Hydrogen ]s are being looked into as a way to provide potentially cheap, ]- free ]. | ||
| == History == | |||
| ⚫ | Hydrogen (] for ''water-maker'', from ] ''hudôr'', "water and ''gennen'' "generate") was first recognized as a distinct substance in ] by ]. ] gave the element its name. | ||
| ⚫ | == Occurrence == | ||
| Hydrogen is the most ] element in the universe, making up 75% of normal matter by ] and over 90% by number of ]s. This element is found in great abundance ]s and gas giant planets. Relative to its great abundance elsewhere, hydrogen is very rare in the ]'s atmosphere (1 ] by volume). The most common source for this element on earth is ] which is composed two parts hydrogen to one part ] (H<sub>2</sub>O). Other sources are; most forms of organic matter which includes all known life forms, ], ]s and ]. ] (]H<sub>4</sub>), which is a byproduct of organic decay, is an increasingly important source of hydrogen. | |||
| Hydrogen is prepared in several different ways; ] on heated ], ] decomposition with heat, action of ] or ] ] on ], water ], or by displacement from ]s with certain ]s. | |||
| ⚫ | Deuterium is used in nuclear applications as a moderator to slow down ]s, and deuterium compounds have applications in ] and ] in studies of reaction ]s. |
||
| == |
== Compounds == | ||
| ⚫ | The lightest of all gases, hydrogen combines with most other elements to form compounds. Hydrogen has an ] of 2.2, so it forms compounds where it is the more non-metallic and where it is the more metallic element. The former are called hydrides, where hydrogen either exists as H<sup>-</sup> ions or just as a solute within the other element (as in ] hydride). The latter tend to be ], since the H<sup>+</sup> ion would be a bare nucleus and so has a strong tendency to pull electrons to itself. Thus even in an ]ic solution one sees ions like H<sub>3</sub>O<sup>+</sup> as the protons latch on to something. | ||
| ⚫ | Hydrogen (] for ''water-maker'', from ] ''hudôr'', "water and ''gennen'' "generate") was first recognized as a distinct substance in ] by ]. ] gave the element its name. | ||
| ⚫ | == Occurrence == | ||
| Hydrogen is the most ] element in the universe, making up around 75% of normal matter (some sources claim 90%). Hydrogen is the lightest chemical element; its atoms consist of a single ] and ]. The most common ] has no ]s, although there are two others - ] with one, and radioactive ] with two neutrons. | |||
| == Compounds == | |||
| ⚫ | Hydrogen has an ] of 2.2, so it forms compounds where it is the more non-metallic and where it is the more metallic element. The former are called hydrides, where hydrogen either exists as H<sup>-</sup> ions or just as a solute within the other element (as in ] hydride). The latter tend to be ], since the H<sup>+</sup> ion would be a bare nucleus and so has a strong tendency to pull electrons to itself. Thus even in an ]ic solution one sees ions like H<sub>3</sub>O<sup>+</sup> as the protons latch on to something. | ||
| Hydrogen combines with oxygen to form ], H<sub>2</sub>O, and releases a lot of energy in doing so, burning ] in air. Deuterium oxide, or D<sub>2</sub>O, is commonly referred to as ]. | Hydrogen combines with oxygen to form ], H<sub>2</sub>O, and releases a lot of energy in doing so, burning ] in air. Deuterium oxide, or D<sub>2</sub>O, is commonly referred to as ]. | ||
| Hydrogen forms a vast array of compounds with ]. Because of their association with living things, these compounds are called ]s, and the study of the properties of these compounds is called ]. | Hydrogen forms a vast array of compounds with ]. Because of their association with living things, these compounds are called ]s, and the study of the properties of these compounds is called ]. | ||
| == |
== Forms == | ||
| Under normal conditions hydrogen gas is a mix of two different kinds of ]s which differ from one another by the "direction" that their ] spin. These two forms are known as ortho- and para-hydrogen (this is different than ]s, see below). | |||
| ⚫ | |||
| ⚫ | == Precautions == | ||
| ⚫ | <font color="red">Hydrogen is a highly ] gas. It also reacts violently with ] and ].</font> | ||
| At ]s normal hydrogen is comprised of 25% of the para form and 75% of the ortho form. The ortho form can't be prepared in its pure state. The two forms of hydrogen differ in energy and this results in slightly different physical properties. For example, the melting and boiling points of parahydrogen are about 0.1 ° K lower than orthohydrogen (the so-called "normal" form). | |||
| ⚫ | D<sub>2</sub>O, or ], is toxic to many species. The quantity required to kill a human, however, is substantial. | ||
| == Isotopes == | |||
| ⚫ | The most common hydrogen ], protium, has no ]s, although there are two others - deuterium with one, and radioactive tritium with two neutrons. The two stable isotopes are protium (H-1) and deuterium (H-2, D). Deuterium comprises 0.0184-0.0082% of all hydrogen (]); ratios of deuterium to protium are reported relative to the ] standard reference water. A radioactive isotope, tritium (T or H-3) is another isotope and has one proton and two neutrons. | ||
| Hydrogen is the only element that has different names for its isotopes. | |||
| ⚫ | == Precautions == | ||
| ⚫ | <font color="red">Hydrogen is a highly ] gas. It also reacts violently with ] and ].</font> | ||
| ⚫ | D<sub>2</sub>O, or ], is toxic to many species. The quantity required to kill a human, however, is substantial. | ||
| See also: ], ], ], ] | See also: ], ], ], ] | ||
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Revision as of 08:04, 14 October 2002
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Hydrogen is a chemical element in the periodic table that has the symbol H and atomic number 1. A colorless, odorless, non-metal, univalent, highly flammable diatomic gas, hydrogen is the lightest and most abundant element in the universe and is present in water and in all organic compounds and living organisms. Hydrogen is able to chemically react with most elements. Stars in their main sequence overwhelmingly composed of hydrogen in its plasma state. This element is used as a lifting gas, an alternative fuel, the power-source of fuel cells
Notable Characteristics
Hydrogen is the lightest chemical element with its most common isotope consisting of just a single proton and electron. At standard temperature and pressure conditions, hydrogen forms a diatomic gas, H2, with a boiling point of only 20.27 K and a melting point of 14.02 K. Under exceedingly high pressures, like those found at the center of gas giants, the molecules lose their identity and the hydrogen becomes a liquid metal. Under the exceedingly low pressure conditions found in space, hydrogen tends to exist as individual atoms, simply because there is no way for them to combine; clouds of H2 form and are associated with star formation.
This element plays a vital role in powering the universe through the proton-proton reaction and carbon-nitrogen cycle (these are nuclear fusion processes that release huge amounts of energy through combining two hydrogen atom into one helium).
Applications
Large quantities of hydrogen are needed industrially, notably in the Haber process for the production of ammonia, the hydrogenation of fats and oils, and the production of methanol. Other uses that require hydrogen;
- hydrodealkylation, hydrodesulfurization, and hydrocracking.
- manufacture of hydrochloric acid, welding, rocket fuels, and the reduction of metallic ores.
- liquid hydrogen is used in cryogenic research including superconductivity studies,
- tritium is produced in nuclear reactors and is used in hydrogen bomb construction.
- It is fourteen and a half times lighter than air and at one time was widely used as a lifting agent in balloons and zeppelins.
- Deuterium is used in nuclear applications as a moderator to slow down neutrons, and deuterium compounds have applications in chemistry and biology in studies of reaction isotope effects.
- Tritium is used as an isotopic label in the biosciences, as a radiation source in luminous paints.
Hydrogen can be burned in internal combustion engines, and a fleet of hydrogen burning cars is maintained by Chrysler-BMW. Hydrogen fuel cells are being looked into as a way to provide potentially cheap, pollution- free power.
History
Hydrogen (French for water-maker, from Greek hudôr, "water and gennen "generate") was first recognized as a distinct substance in 1776 by Henry Cavendish. Antoine Lavoisier gave the element its name.
Occurrence
Hydrogen is the most abundant element in the universe, making up 75% of normal matter by mass and over 90% by number of atoms. This element is found in great abundance stars and gas giant planets. Relative to its great abundance elsewhere, hydrogen is very rare in the earth's atmosphere (1 ppm by volume). The most common source for this element on earth is water which is composed two parts hydrogen to one part oxygen (H2O). Other sources are; most forms of organic matter which includes all known life forms, coal, fossil fuels and natural gas. Methane (CH4), which is a byproduct of organic decay, is an increasingly important source of hydrogen.
Hydrogen is prepared in several different ways; steam on heated carbon, hydrocarbon decomposition with heat, action of sodium or potassium hydroxide on aluminum, water electrolysis, or by displacement from acids with certain metals.
Compounds
The lightest of all gases, hydrogen combines with most other elements to form compounds. Hydrogen has an electronegativity of 2.2, so it forms compounds where it is the more non-metallic and where it is the more metallic element. The former are called hydrides, where hydrogen either exists as H ions or just as a solute within the other element (as in Palladium hydride). The latter tend to be covalent, since the H ion would be a bare nucleus and so has a strong tendency to pull electrons to itself. Thus even in an acidic solution one sees ions like H3O as the protons latch on to something.
Hydrogen combines with oxygen to form water, H2O, and releases a lot of energy in doing so, burning explosively in air. Deuterium oxide, or D2O, is commonly referred to as heavy water.
Hydrogen forms a vast array of compounds with carbon. Because of their association with living things, these compounds are called organic compounds, and the study of the properties of these compounds is called organic chemistry.
Forms
Under normal conditions hydrogen gas is a mix of two different kinds of molecules which differ from one another by the "direction" that their [[electron[[s' and nuclei spin. These two forms are known as ortho- and para-hydrogen (this is different than isotopes, see below).
At standard conditions normal hydrogen is comprised of 25% of the para form and 75% of the ortho form. The ortho form can't be prepared in its pure state. The two forms of hydrogen differ in energy and this results in slightly different physical properties. For example, the melting and boiling points of parahydrogen are about 0.1 ° K lower than orthohydrogen (the so-called "normal" form).
Isotopes
The most common hydrogen isotope, protium, has no neutrons, although there are two others - deuterium with one, and radioactive tritium with two neutrons. The two stable isotopes are protium (H-1) and deuterium (H-2, D). Deuterium comprises 0.0184-0.0082% of all hydrogen (IUPAC); ratios of deuterium to protium are reported relative to the VSMOW standard reference water. A radioactive isotope, tritium (T or H-3) is another isotope and has one proton and two neutrons.
Hydrogen is the only element that has different names for its isotopes.
Precautions
Hydrogen is a highly flammable gas. It also reacts violently with chlorine and fluorine. D2O, or heavy water, is toxic to many species. The quantity required to kill a human, however, is substantial.
See also: Periodic Table, hydrogen bond, hydrogen atom, Antihydrogen