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Hydrogen | |||
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).
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:
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.
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.
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.
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. These both form acids. 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 also 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.
Under normal conditions hydrogen gas is a mix of two different kinds of molecules which differ from one another by the "direction" that their electrons' 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).
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) has one proton and two neutrons.
Hydrogen is the only element that has different names for its isotopes.
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.
But at the instant of his appearance on the stage, the
burst into laughter, hisses, and mock applause, so that he was struck
whose _Stukely_ has played, was compelled, therefore, to strike _Dawson_
faithfully but that his want of confidence ruined him. Mr. Fredericks
not play.html">play under his full name, but as Mr. J. Wilkes--and he bore the
associated freely with such of the subordinate actors as he liked; but
might, had he chosen, advanced himself socially, if not artistically.
things, a mock _Richard III_., to which he allowed Wilkes Booth to play
some energy, and obtain some applause. But, in general, he was stumbling
him trip up and receive suppressed hisses. He lacked enterprise; other
them to memory, in the hope that their real interpreter might not come
quite a celebrated actor. He was getting, if I correctly remember, only
too slow or indifferent to get on the weather side of such chances. He
the first to be walked off in case of strait, as was Wilkes Booth. He
dollars in all that time. The Kellers arrived; they cut down the
Philadelphia by his failure as in the world by his crime.
About this time a manager named Kunkle gave Booth a salary of twenty
order of parts, and played them better, Winning applauses from the easy
never wondered why many actors were strongly predisposed toward the
hospitable, lounging, buzzing character of the southerner is entirely
"hang-up-your-hatativeness," which is the rule and the demand in
because they are there. The South took them into affable.
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