149 résultats pour "chemistry"

• Tantalum - chemistry.

• Selenium - chemistry.

• pH - chemistry.

• Manganese - chemistry.

• Radon - chemistry.

• Platinum - chemistry.

• Neon - chemistry.

• Boron - chemistry.

• Darmstadtium - chemistry.

• Zinc - chemistry.

• Deuterium - chemistry.

• Magnesium - chemistry.

• Radium - chemistry.

• Titanium - chemistry.

• Nitrogen - chemistry.

• Phosphorus - chemistry.

• Arsenic - chemistry.

• Fluorine - chemistry.

• Nickel - chemistry.

• Tin - chemistry.

• Potassium - chemistry.

• Oxygen - chemistry.

• Silicon - chemistry.

• Silver - chemistry.

• Aluminum - chemistry.

• Uranium - chemistry.

• Iron - chemistry.

• Lead - chemistry.

  compounds are considered serious hazards for children. Children are especially at hazard from lead, even at levels once thought safe. Lead can reduce intelligence,delay motor development, impair memory, and cause hearing problems and troubles in balance. In adults, one lead hazard at levels once thought safe is that ofincreased blood pressure. Present-day treatment of lead poisoning includes the administration of calcium disodium ethylenediaminetetraacidic acid, or EDTA, a chelatingagent; lead i...

• Sulfur - chemistry.

• Helium - chemistry.

  the bends. This synthetic atmosphere is also used in medicine to relieve sufferers of respiratory difficulties because helium moves more easily than nitrogen throughconstricted respiratory passages. In surgery, beams of ionized helium from synchrocyclotron sources are proving useful in treating eye tumors, by stabilizing or evenshrinking the tumors. Such beams are also used to shrink blood-vessel malformations in the brains of patients. Helium is used in inert-gas arc welding for light metals, s...

• Gold - chemistry.

  producers of gold during this period. Spain's domination in South America resulted, in the 16th century, in a large increase in gold produced in the New World; someresulted from simple seizure of gold from the Native Americans, who had long mined the metal. In the same century Mexico contributed about 9 percent of the totalworld production. Gold was discovered in Australia in February 1851, and rich fields were found there. By the middle of the 19th century the United States produced a considera...

• Air - chemistry.

  lighting systems, fertilizers, and semiconductors (substances used to make the chips in computers, calculators, televisions, microwave ovens, and many other electronicdevices). A Oxygen More than half of the oxygen produced in the United States is used by the steel industry, which injects the gas into basic oxygen furnaces to heat and produce steel(see Iron and Steel Manufacture: Basic Oxygen Process ). Metalworkers also combine oxygen with acetylene to produce high-temperature torch flames th...

• Water - chemistry.

  flourides in drinking water has been found to reduce tooth decay. See Fluorine. Seawater contains, in addition to concentrated amounts of sodium chloride, or salt, many other soluble compounds, as the impure waters of rivers and streams areconstantly feeding the oceans. At the same time, pure water is continually lost by the process of evaporation, and as a result the proportion of the impurities that givethe oceans their saline character is increased. See Ocean and Oceanography. VII WATER...

• Physical Constants - chemistry.

• Palladium (element) - chemistry.

• Element 112 - chemistry.

• Amino Acids - chemistry.

• Copper (element) - chemistry.

• Mercury (element) - chemistry.

• Periodic Table - chemistry.

• Acids and Bases - chemistry.

• Astrobiology - astronomy.

  water to help reactions along. American chemists Stanley Miller and Harold Urey tested part of Oparin and Haldane’s hypothesis in the early 1950s by simulating conditions of the early Earth. In whathas become known as the Miller-Urey experiment, the two scientists connected two flasks with a loop of glass tubing that allowed the gases to pass between the flasks.They filled the upper flask with methane, ammonia, and hydrogen—components thought to have been in the early atmosphere. They filled the...

• Electron I INTRODUCTION Models of the Atom Once scientists discovered the electron, they set out to explain how electrons behave in atoms.

  Electron Density and Orbital ShapesAtomic orbitals are mathematical descriptions of where the electrons in an atom (or molecule) are most likely to be found.These descriptions are obtained by solving an equation known as the Schrödinger equation, which expresses ourknowledge of the atomic world. As the angular momentum and energy of an electron increases, it tends to reside indifferently shaped orbitals. The orbitals corresponding to the three lowest energy states are s, p, and d, respectively....

• Geology.

  terminology. Today the geologic time scale is generally agreed upon and used by scientists around the world, dividing time into eons, eras, periods, and epochs. Everyfew years, the numerical time scale is refined based on new evidence, and geologists publish an update. Geologists use several methods to determine geologic time. These methods include physical stratigraphy, or the placement of events in the order of their occurrence,and biostratigraphy, which uses fossils to determine geologic time...

• Natural Satellite - astronomy.

  Titan, Saturn’s largest moon, also has few impact craters. Although icy volcanism from water and ammonia may occur along with some tectonic activity, Titan’s youngsurface is most likely the result of weather processes. Titan’s dense, cold atmosphere precipitates particles of complex organic molecules that accumulate as dunes andmountains. Methane rain erodes the surface and creates lakes at the moon’s poles. Triton’s young surface also may result from processes in its atmosphere, as well aserupt...

• Neutron I INTRODUCTION Neutron, electrically neutral elementary particle that is part of the nucleus of the atom.

  Beta DecayBeta decay can occur in two ways. As shown on the left, a neutron turns into a proton by emitting an antineutrino and anegatively charged beta particle. As shown on the right, a proton turns into a neutron by emitting a neutrino and apositively charged beta particle. Positive beta particles are called positrons and negative beta particles are called electrons.After the decay, the nucleus of the atom contains either one less or one more proton. Beta decay changes an atom of oneelement i...

• Colleges and Universities.

  and (3) large universities that include undergraduate programs in addition to graduate and professional schools. D Graduate and Professional Schools Professional schools are typically divisions of large universities. They offer specialized education in a variety of professional fields, such as education, business, medicine,law, social work, agriculture, journalism, architecture, fine arts, nursing, engineering, and music. Some professional schools offer four- or five-year programs leading toa b...

• Library (institution).

  rooms, special galleries for exhibitions, auditoriums for lectures or concerts, computer rooms, children’s rooms, photocopy rooms, and classrooms. A3 Lending Materials As part of their mission to provide information resources to the community, public libraries allow users to borrow items from their collections for limited amounts of time.To be eligible to borrow public library materials, a user must register her or his name, address, and other basic information with the local library’s circulat...

• The way in which companies frame themselves, their products and their clients