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Compounds of hydrogen are often called hydrides, a term that is used fairly loosely. The term "hydride" suggests that the H atom has acquired a negative or anionic character, denoted H−, and is used when hydrogen forms a compound with a more electropositive element. The existence of the hydride anion, suggested by Gilb...
Although hydrides can be formed with almost all main-group elements, the number and combination of possible compounds varies widely; for example, there are over 100 binary borane hydrides known, but only one binary aluminium hydride. Binary indium hydride has not yet been identified, although larger complexes exist.
In inorganic chemistry, hydrides can also serve as bridging ligands that link two metal centers in a coordination complex. This function is particularly common in group 13 elements, especially in boranes (boron hydrides) and aluminium complexes, as well as in clustered carboranes.
Oxidation of hydrogen removes its electron and gives H+, which contains no electrons and a nucleus which is usually composed of one proton. That is why H+ is often called a proton. This species is central to discussion of acids. Under the Bronsted-Lowry theory, acids are proton donors, while bases are proton acceptors.
A bare proton, H+, cannot exist in solution or in ionic crystals, because of its unstoppable attraction to other atoms or molecules with electrons. Except at the high temperatures associated with plasmas, such protons cannot be removed from the electron clouds of atoms and molecules, and will remain attached to them. H...
To avoid the implication of the naked "solvated proton" in solution, acidic aqueous solutions are sometimes considered to contain a less unlikely fictitious species, termed the "hydronium ion" (H 3O+). However, even in this case, such solvated hydrogen cations are more realistically conceived as being organized into cl...
Although exotic on Earth, one of the most common ions in the universe is the H+ 3 ion, known as protonated molecular hydrogen or the trihydrogen cation.
Hydrogen has three naturally occurring isotopes, denoted 1H, 2H and 3H. Other, highly unstable nuclei (4H to 7H) have been synthesized in the laboratory but not observed in nature.
Hydrogen is the only element that has different names for its isotopes in common use today. During the early study of radioactivity, various heavy radioactive isotopes were given their own names, but such names are no longer used, except for deuterium and tritium. The symbols D and T (instead of 2H and 3H) are sometime...
In 1671, Robert Boyle discovered and described the reaction between iron filings and dilute acids, which results in the production of hydrogen gas. In 1766, Henry Cavendish was the first to recognize hydrogen gas as a discrete substance, by naming the gas from a metal-acid reaction "flammable air". He speculated that "...
Lavoisier produced hydrogen for his experiments on mass conservation by reacting a flux of steam with metallic iron through an incandescent iron tube heated in a fire. Anaerobic oxidation of iron by the protons of water at high temperature can be schematically represented by the set of following reactions:
Hydrogen was liquefied for the first time by James Dewar in 1898 by using regenerative cooling and his invention, the vacuum flask. He produced solid hydrogen the next year. Deuterium was discovered in December 1931 by Harold Urey, and tritium was prepared in 1934 by Ernest Rutherford, Mark Oliphant, and Paul Harteck. ...
The first hydrogen-filled balloon was invented by Jacques Charles in 1783. Hydrogen provided the lift for the first reliable form of air-travel following the 1852 invention of the first hydrogen-lifted airship by Henri Giffard. German count Ferdinand von Zeppelin promoted the idea of rigid airships lifted by hydrogen t...
The first non-stop transatlantic crossing was made by the British airship R34 in 1919. Regular passenger service resumed in the 1920s and the discovery of helium reserves in the United States promised increased safety, but the U.S. government refused to sell the gas for this purpose. Therefore, H2 was used in the Hinde...
In the same year the first hydrogen-cooled turbogenerator went into service with gaseous hydrogen as a coolant in the rotor and the stator in 1937 at Dayton, Ohio, by the Dayton Power & Light Co.; because of the thermal conductivity of hydrogen gas, this is the most common type in its field today.
The nickel hydrogen battery was used for the first time in 1977 aboard the U.S. Navy's Navigation technology satellite-2 (NTS-2). For example, the ISS, Mars Odyssey and the Mars Global Surveyor are equipped with nickel-hydrogen batteries. In the dark part of its orbit, the Hubble Space Telescope is also powered by nick...
Because of its simple atomic structure, consisting only of a proton and an electron, the hydrogen atom, together with the spectrum of light produced from it or absorbed by it, has been central to the development of the theory of atomic structure. Furthermore, the corresponding simplicity of the hydrogen molecule and th...
One of the first quantum effects to be explicitly noticed (but not understood at the time) was a Maxwell observation involving hydrogen, half a century before full quantum mechanical theory arrived. Maxwell observed that the specific heat capacity of H2 unaccountably departs from that of a diatomic gas below room tempe...
Hydrogen, as atomic H, is the most abundant chemical element in the universe, making up 75% of normal matter by mass and over 90% by number of atoms (most of the mass of the universe, however, is not in the form of chemical-element type matter, but rather is postulated to occur as yet-undetected forms of mass such as d...
Throughout the universe, hydrogen is mostly found in the atomic and plasma states whose properties are quite different from molecular hydrogen. As a plasma, hydrogen's electron and proton are not bound together, resulting in very high electrical conductivity and high emissivity (producing the light from the Sun and oth...
Under ordinary conditions on Earth, elemental hydrogen exists as the diatomic gas, H2. However, hydrogen gas is very rare in the Earth's atmosphere (1 ppm by volume) because of its light weight, which enables it to escape from Earth's gravity more easily than heavier gases. However, hydrogen is the third most abundant ...
A molecular form called protonated molecular hydrogen (H+ 3) is found in the interstellar medium, where it is generated by ionization of molecular hydrogen from cosmic rays. This charged ion has also been observed in the upper atmosphere of the planet Jupiter. The ion is relatively stable in the environment of outer sp...
H 2 is produced in chemistry and biology laboratories, often as a by-product of other reactions; in industry for the hydrogenation of unsaturated substrates; and in nature as a means of expelling reducing equivalents in biochemical reactions.
The electrolysis of water is a simple method of producing hydrogen. A low voltage current is run through the water, and gaseous oxygen forms at the anode while gaseous hydrogen forms at the cathode. Typically the cathode is made from platinum or another inert metal when producing hydrogen for storage. If, however, the ...
An alloy of aluminium and gallium in pellet form added to water can be used to generate hydrogen. The process also produces alumina, but the expensive gallium, which prevents the formation of an oxide skin on the pellets, can be re-used. This has important potential implications for a hydrogen economy, as hydrogen can ...
Hydrogen can be prepared in several different ways, but economically the most important processes involve removal of hydrogen from hydrocarbons. Commercial bulk hydrogen is usually produced by the steam reforming of natural gas. At high temperatures (1000–1400 K, 700–1100 °C or 1300–2000 °F), steam (water vapor) reacts...
This reaction is favored at low pressures but is nonetheless conducted at high pressures (2.0 MPa, 20 atm or 600 inHg). This is because high-pressure H 2 is the most marketable product and Pressure Swing Adsorption (PSA) purification systems work better at higher pressures. The product mixture is known as "synthesis ga...
Consequently, steam reforming typically employs an excess of H 2O. Additional hydrogen can be recovered from the steam by use of carbon monoxide through the water gas shift reaction, especially with an iron oxide catalyst. This reaction is also a common industrial source of carbon dioxide:
Hydrogen is sometimes produced and consumed in the same industrial process, without being separated. In the Haber process for the production of ammonia, hydrogen is generated from natural gas. Electrolysis of brine to yield chlorine also produces hydrogen as a co-product.
There are more than 200 thermochemical cycles which can be used for water splitting, around a dozen of these cycles such as the iron oxide cycle, cerium(IV) oxide–cerium(III) oxide cycle, zinc zinc-oxide cycle, sulfur-iodine cycle, copper-chlorine cycle and hybrid sulfur cycle are under research and in testing phase to...
Under anaerobic conditions, iron and steel alloys are slowly oxidized by the protons of water concomitantly reduced in molecular hydrogen (H 2). The anaerobic corrosion of iron leads first to the formation of ferrous hydroxide (green rust) and can be described by the following reaction:
In its turn, under anaerobic conditions, the ferrous hydroxide (Fe(OH) 2 ) can be oxidized by the protons of water to form magnetite and molecular hydrogen. This process is described by the Schikorr reaction:
In the absence of atmospheric oxygen (O 2), in deep geological conditions prevailing far away from Earth atmosphere, hydrogen (H 2) is produced during the process of serpentinization by the anaerobic oxidation by the water protons (H+) of the ferrous (Fe2+) silicate present in the crystal lattice of the fayalite (Fe 2S...
From all the fault gases formed in power transformers, hydrogen is the most common and is generated under most fault conditions; thus, formation of hydrogen is an early indication of serious problems in the transformer's life cycle.
Large quantities of H 2 are needed in the petroleum and chemical industries. The largest application of H 2 is for the processing ("upgrading") of fossil fuels, and in the production of ammonia. The key consumers of H 2 in the petrochemical plant include hydrodealkylation, hydrodesulfurization, and hydrocracking. H 2 h...
Hydrogen is highly soluble in many rare earth and transition metals and is soluble in both nanocrystalline and amorphous metals. Hydrogen solubility in metals is influenced by local distortions or impurities in the crystal lattice. These properties may be useful when hydrogen is purified by passage through hot palladiu...
Apart from its use as a reactant, H 2 has wide applications in physics and engineering. It is used as a shielding gas in welding methods such as atomic hydrogen welding. H2 is used as the rotor coolant in electrical generators at power stations, because it has the highest thermal conductivity of any gas. Liquid H2 is u...
In more recent applications, hydrogen is used pure or mixed with nitrogen (sometimes called forming gas) as a tracer gas for minute leak detection. Applications can be found in the automotive, chemical, power generation, aerospace, and telecommunications industries. Hydrogen is an authorized food additive (E 949) that ...
Hydrogen's rarer isotopes also each have specific applications. Deuterium (hydrogen-2) is used in nuclear fission applications as a moderator to slow neutrons, and in nuclear fusion reactions. Deuterium compounds have applications in chemistry and biology in studies of reaction isotope effects. Tritium (hydrogen-3), pr...
Hydrogen is commonly used in power stations as a coolant in generators due to a number of favorable properties that are a direct result of its light diatomic molecules. These include low density, low viscosity, and the highest specific heat and thermal conductivity of all gases.
Hydrogen is not an energy resource, except in the hypothetical context of commercial nuclear fusion power plants using deuterium or tritium, a technology presently far from development. The Sun's energy comes from nuclear fusion of hydrogen, but this process is difficult to achieve controllably on Earth. Elemental hydr...
The energy density per unit volume of both liquid hydrogen and compressed hydrogen gas at any practicable pressure is significantly less than that of traditional fuel sources, although the energy density per unit fuel mass is higher. Nevertheless, elemental hydrogen has been widely discussed in the context of energy, a...
Hydrogen is employed to saturate broken ("dangling") bonds of amorphous silicon and amorphous carbon that helps stabilizing material properties. It is also a potential electron donor in various oxide materials, including ZnO, SnO2, CdO, MgO, ZrO2, HfO2, La2O3, Y2O3, TiO2, SrTiO3, LaAlO3, SiO2, Al2O3, ZrSiO4, HfSiO4, an...
H2 is a product of some types of anaerobic metabolism and is produced by several microorganisms, usually via reactions catalyzed by iron- or nickel-containing enzymes called hydrogenases. These enzymes catalyze the reversible redox reaction between H2 and its component two protons and two electrons. Creation of hydroge...
Water splitting, in which water is decomposed into its component protons, electrons, and oxygen, occurs in the light reactions in all photosynthetic organisms. Some such organisms, including the alga Chlamydomonas reinhardtii and cyanobacteria, have evolved a second step in the dark reactions in which protons and elect...
Hydrogen poses a number of hazards to human safety, from potential detonations and fires when mixed with air to being an asphyxiant in its pure, oxygen-free form. In addition, liquid hydrogen is a cryogen and presents dangers (such as frostbite) associated with very cold liquids. Hydrogen dissolves in many metals, and,...
Even interpreting the hydrogen data (including safety data) is confounded by a number of phenomena. Many physical and chemical properties of hydrogen depend on the parahydrogen/orthohydrogen ratio (it often takes days or weeks at a given temperature to reach the equilibrium ratio, for which the data is usually given). ...
A web browser (commonly referred to as a browser) is a software application for retrieving, presenting, and traversing information resources on the World Wide Web. An information resource is identified by a Uniform Resource Identifier (URI/URL) and may be a web page, image, video or other piece of content. Hyperlinks p...
Although browsers are primarily intended to use the World Wide Web, they can also be used to access information provided by web servers in private networks or files in file systems.
The first web browser was invented in 1990 by Sir Tim Berners-Lee. Berners-Lee is the director of the World Wide Web Consortium (W3C), which oversees the Web's continued development, and is also the founder of the World Wide Web Foundation. His browser was called WorldWideWeb and later renamed Nexus.
In 1993, browser software was further innovated by Marc Andreessen with the release of Mosaic, "the world's first popular browser", which made the World Wide Web system easy to use and more accessible to the average person. Andreesen's browser sparked the internet boom of the 1990s. The introduction of Mosaic in 1993 –...
Microsoft responded with its Internet Explorer in 1995, also heavily influenced by Mosaic, initiating the industry's first browser war. Bundled with Windows, Internet Explorer gained dominance in the web browser market; Internet Explorer usage share peaked at over 95% by 2002.
Opera debuted in 1996; it has never achieved widespread use, having less than 2% browser usage share as of February 2012 according to Net Applications. Its Opera-mini version has an additive share, in April 2011 amounting to 1.1% of overall browser use, but focused on the fast-growing mobile phone web browser market, b...
In 1998, Netscape launched what was to become the Mozilla Foundation in an attempt to produce a competitive browser using the open source software model. That browser would eventually evolve into Firefox, which developed a respectable following while still in the beta stage of development; shortly after the release of ...
Apple's Safari had its first beta release in January 2003; as of April 2011, it had a dominant share of Apple-based web browsing, accounting for just over 7% of the entire browser market.
The most recent major entrant to the browser market is Chrome, first released in September 2008. Chrome's take-up has increased significantly year by year, by doubling its usage share from 8% to 16% by August 2011. This increase seems largely to be at the expense of Internet Explorer, whose share has tended to decrease...
Internet Explorer, on the other hand, was bundled free with the Windows operating system (and was also downloadable free), and therefore it was funded partly by the sales of Windows to computer manufacturers and direct to users. Internet Explorer also used to be available for the Mac. It is likely that releasing IE for...
In January 2009, the European Commission announced it would investigate the bundling of Internet Explorer with Windows operating systems from Microsoft, saying "Microsoft's tying of Internet Explorer to the Windows operating system harms competition between web browsers, undermines product innovation and ultimately red...
Safari and Mobile Safari were likewise always included with OS X and iOS respectively, so, similarly, they were originally funded by sales of Apple computers and mobile devices, and formed part of the overall Apple experience to customers.
Today, most commercial web browsers are paid by search engine companies to make their engine default, or to include them as another option. For example, Google pays Mozilla, the maker of Firefox, to make Google Search the default search engine in Firefox. Mozilla makes enough money from this deal that it does not need ...
The primary purpose of a web browser is to bring information resources to the user ("retrieval" or "fetching"), allowing them to view the information ("display", "rendering"), and then access other information ("navigation", "following links").
This process begins when the user inputs a Uniform Resource Locator (URL), for example http://en.wikipedia.org/, into the browser. The prefix of the URL, the Uniform Resource Identifier or URI, determines how the URL will be interpreted. The most commonly used kind of URI starts with http: and identifies a resource to ...
In the case of http, https, file, and others, once the resource has been retrieved the web browser will display it. HTML and associated content (image files, formatting information such as CSS, etc.) is passed to the browser's layout engine to be transformed from markup to an interactive document, a process known as "r...
Information resources may contain hyperlinks to other information resources. Each link contains the URI of a resource to go to. When a link is clicked, the browser navigates to the resource indicated by the link's target URI, and the process of bringing content to the user begins again.
Available web browsers range in features from minimal, text-based user interfaces with bare-bones support for HTML to rich user interfaces supporting a wide variety of file formats and protocols. Browsers which include additional components to support e-mail, Usenet news, and Internet Relay Chat (IRC), are sometimes re...
All major web browsers allow the user to open multiple information resources at the same time, either in different browser windows or in different tabs of the same window. Major browsers also include pop-up blockers to prevent unwanted windows from "popping up" without the user's consent.
A browser extension is a computer program that extends the functionality of a web browser. Every major web browser supports the development of browser extensions.
Most web browsers can display a list of web pages that the user has bookmarked so that the user can quickly return to them. Bookmarks are also called "Favorites" in Internet Explorer. In addition, all major web browsers have some form of built-in web feed aggregator. In Firefox, web feeds are formatted as "live bookmar...
Most browsers support HTTP Secure and offer quick and easy ways to delete the web cache, download history, form and search history, cookies, and browsing history. For a comparison of the current security vulnerabilities of browsers, see comparison of web browsers.
Early web browsers supported only a very simple version of HTML. The rapid development of proprietary web browsers led to the development of non-standard dialects of HTML, leading to problems with interoperability. Modern web browsers support a combination of standards-based and de facto HTML and XHTML, which should be...
Web browsers consist of a user interface, layout engine, rendering engine, JavaScript interpreter, UI backend, networking component and data persistence component. These components achieve different functionalities of a web browser and together provide all capabilities of a web browser.
Boston (pronounced i/ˈbɒstən/) is the capital and largest city of the Commonwealth of Massachusetts in the United States. Boston also served as the historic county seat of Suffolk County until Massachusetts disbanded county government in 1999. The city proper covers 48 square miles (124 km2) with an estimated populatio...
One of the oldest cities in the United States, Boston was founded on the Shawmut Peninsula in 1630 by Puritan settlers from England. It was the scene of several key events of the American Revolution, such as the Boston Massacre, the Boston Tea Party, the Battle of Bunker Hill, and the Siege of Boston. Upon American ind...
The area's many colleges and universities make Boston an international center of higher education and medicine, and the city is considered to be a world leader in innovation. Boston's economic base also includes finance, professional and business services, biotechnology, information technology, and government activitie...
Boston's early European settlers had first called the area Trimountaine (after its "three mountains"—only traces of which remain today) but later renamed it Boston after Boston, Lincolnshire, England, the origin of several prominent colonists. The renaming, on September 7, 1630 (Old Style),[b] was by Puritan colonists ...
In 1629, the Massachusetts Bay Colony's first governor, John Winthrop, led the signing of the Cambridge Agreement, a key founding document of the city. Puritan ethics and their focus on education influenced its early history; America's first public school was founded in Boston in 1635. Over the next 130 years, the city...
Many of the crucial events of the American Revolution—the Boston Massacre, the Boston Tea Party, Paul Revere's midnight ride, the battles of Lexington and Concord and Bunker Hill, the Siege of Boston, and many others—occurred in or near Boston. After the Revolution, Boston's long seafaring tradition helped make it one ...
The Embargo Act of 1807, adopted during the Napoleonic Wars, and the War of 1812 significantly curtailed Boston's harbor activity. Although foreign trade returned after these hostilities, Boston's merchants had found alternatives for their capital investments in the interim. Manufacturing became an important component ...
During this period Boston flourished culturally as well, admired for its rarefied literary life and generous artistic patronage, with members of old Boston families—eventually dubbed Boston Brahmins—coming to be regarded as the nation's social and cultural elites.
Boston was an early port of the Atlantic triangular slave trade in the New England colonies, but was soon overtaken by Salem, Massachusetts and Newport, Rhode Island. Eventually Boston became a center of the abolitionist movement. The city reacted strongly to the Fugitive Slave Law of 1850, contributing to President Fr...
In 1822, the citizens of Boston voted to change the official name from "the Town of Boston" to "the City of Boston", and on March 4, 1822, the people of Boston accepted the charter incorporating the City. At the time Boston was chartered as a city, the population was about 46,226, while the area of the city was only 4....
In the 1820s, Boston's population grew rapidly, and the city's ethnic composition changed dramatically with the first wave of European immigrants. Irish immigrants dominated the first wave of newcomers during this period, especially following the Irish Potato Famine; by 1850, about 35,000 Irish lived in Boston. In the ...
Between 1631 and 1890, the city tripled its area through land reclamation by filling in marshes, mud flats, and gaps between wharves along the waterfront. The largest reclamation efforts took place during the 19th century; beginning in 1807, the crown of Beacon Hill was used to fill in a 50-acre (20 ha) mill pond that ...
By the early and mid-20th century, the city was in decline as factories became old and obsolete, and businesses moved out of the region for cheaper labor elsewhere. Boston responded by initiating various urban renewal projects under the direction of the Boston Redevelopment Authority (BRA), which was established in 195...
The BRA subsequently reevaluated its approach to urban renewal in its future projects, including the construction of Government Center. In 1965, the first Community Health Center in the United States opened, the Columbia Point Health Center, in the Dorchester neighborhood. It mostly served the massive Columbia Point pu...
Boston is an intellectual, technological, and political center but has lost some important regional institutions, including the acquisition of The Boston Globe by The New York Times, and the loss to mergers and acquisitions of local financial institutions such as FleetBoston Financial, which was acquired by Charlotte-b...
On April 15, 2013, two Chechen Islamist brothers exploded two bombs near the finish line of the Boston Marathon, killing three people and injuring roughly 264.
Boston has an area of 89.6 square miles (232.1 km2)—48.4 square miles (125.4 km2) (54.0%) of land and 41.2 square miles (106.7 km2) (46.0%) of water. The city's official elevation, as measured at Logan International Airport, is 19 ft (5.8 m) above sea level. The highest point in Boston is Bellevue Hill at 330 feet (100...
Boston is surrounded by the "Greater Boston" region and is contiguously bordered by the cities and towns of Winthrop, Revere, Chelsea, Everett, Somerville, Cambridge, Newton, Brookline, Needham, Dedham, Canton, Milton, and Quincy. The Charles River separates Boston from Watertown and the majority of Cambridge, and the ...
Boston is sometimes called a "city of neighborhoods" because of the profusion of diverse subsections; the city government's Office of Neighborhood Services has officially designated 23 neighborhoods.
More than two-thirds of inner Boston's modern land area did not exist when the city was founded, but was created via the gradual filling in of the surrounding tidal areas over the centuries, notably with earth from the leveling or lowering of Boston's three original hills (the "Trimountain", after which Tremont Street ...
Boston has a continental climate with some maritime influence, and using the −3 °C (27 °F) coldest month (January) isotherm, the city lies within the transition zone from a humid subtropical climate (Köppen Cfa) to a humid continental climate (Köppen Dfa), although the suburbs north and west of the city are significant...
Boston's coastal location on the North Atlantic moderates its temperature, but makes the city very prone to Nor'easter weather systems that can produce much snow and rain. The city averages 43.8 inches (1,110 mm) of precipitation a year, with 43.8 inches (111 cm) of snowfall per season. Snowfall increases dramatically ...
Fog is fairly common, particularly in spring and early summer, and the occasional tropical storm or hurricane can threaten the region, especially in late summer and early autumn. Due to its situation along the North Atlantic, the city often receives sea breezes, especially in the late spring, when water temperatures ar...
In 2010, Boston was estimated to have 617,594 residents (a density of 12,200 persons/sq mile, or 4,700/km2) living in 272,481 housing units— a 5% population increase over 2000. The city is the third most densely populated large U.S. city of over half a million residents. Some 1.2 million persons may be within Boston's ...
In the city, the population was spread out with 21.9% at age 19 and under, 14.3% from 20 to 24, 33.2% from 25 to 44, 20.4% from 45 to 64, and 10.1% who were 65 years of age or older. The median age was 30.8 years. For every 100 females, there were 92.0 males. For every 100 females age 18 and over, there were 89.9 males...
The median household income in Boston was $51,739, while the median income for a family was $61,035. Full-time year-round male workers had a median income of $52,544 versus $46,540 for full-time year-round female workers. The per capita income for the city was $33,158. 21.4% of the population and 16.0% of families are ...
In 1950, whites represented 94.7% of Boston's population. From the 1950s to the end of the 20th century, the proportion of non-Hispanic whites in the city declined; in 2000, non-Hispanic whites made up 49.5% of the city's population, making the city majority-minority for the first time. However, in recent years the cit...
People of Irish descent form the largest single ethnic group in the city, making up 15.8% of the population, followed by Italians, accounting for 8.3% of the population. People of West Indian and Caribbean ancestry are another sizable group, at 6.0%, about half of whom are of Haitian ancestry. Over 27,000 Chinese Ameri...
The city has a sizable Jewish population with an estimated 25,000 Jews within the city and 227,000 within the Boston metro area; the number of congregations in Boston is estimated at 22. The adjacent communities of Brookline and Newton are both approximately one-third Jewish.