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Chemistry is the scientific discipline involved with compounds composed of atoms, i.e. elements, and molecules, i.e. combinations of atoms: their composition, structure, properties, behavior and the changes they undergo during a reaction with other compounds. Chemistry addresses topics such as how atoms and molecules interact via chemical bonds to form new chemical compounds. There are four types of chemical bonds: covalent bonds, in which compounds share one or more electron(s); ionic bonds, in which a compound donates one or more electrons to another compound to produce ions (cations and anions); hydrogen bonds; and Van der Waals force bonds.
In the scope of its subject, chemistry occupies an intermediate position between physics and biology. It is sometimes called the central science because it provides a foundation for understanding both basic and applied scientific disciplines at a fundamental level. Examples include plant chemistry (botany), the formation of igneous rocks (geology), how atmospheric ozone is formed and how environmental pollutants are degraded (ecology), the properties of the soil on the moon (astrophysics), how medications work (pharmacology), and how to collect DNA evidence at a crime scene (forensics).
The history of chemistry spans a period from very old times to the present. Since several millennia BC, civilizations were using technologies that would eventually form the basis of the various branches of chemistry. Examples include extracting metals from ores, making pottery and glazes, fermenting beer and wine, extracting chemicals from plants for medicine and perfume, rendering fat into soap, making glass, and making alloys like bronze. Chemistry was preceded by its protoscience, alchemy, which is an intuitive but non-scientific approach to understanding the constituents of matter and their interactions. It was unsuccessful in explaining the nature of matter and its transformations, but, by performing experiments and recording the results, alchemists set the stage for modern chemistry. Chemistry as a body of knowledge distinct from alchemy began to emerge when a clear differentiation was made between them by Robert Boyle in his work The Sceptical Chymist (1661). While both alchemy and chemistry are concerned with matter and its transformations, the crucial difference was given by the scientific method that chemists employed in their work. Chemistry is considered to have become an established science with the work of Antoine Lavoisier, who developed a law of conservation of mass that demanded careful measurement and quantitative observations of chemical phenomena. The history of chemistry is intertwined with the history of thermodynamics, especially through the work of Willard Gibbs. Read more...
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is a silvery metallic chemical element
in the actinide
series of the periodic table
that has the symbol U
and atomic number
92. The heaviest naturally occurring element, uranium is nearly twice as dense as lead
and weakly radioactive
. It occurs naturally in low concentrations (a few parts per million) in soil, rock and water, and is commercially extracted from uranium-bearing minerals
such as uraninite
(see uranium mining
In nature, uranium atoms exist as uranium-238 (99.275%), uranium-235 (0.72%), and a very small amount of uranium-234 (0.0058%). Uranium decays slowly by emitting an alpha particle. The half-life of uranium-238 is about 4.5 billion years and that of uranium-235 is 700 million years, making them useful in dating the age of the Earth (see uranium–thorium dating, uranium–lead dating and uranium–uranium dating). Along with thorium and plutonium, it is one of the three fissile elements, meaning it can easily break apart to become lighter elements. This property of uranium-235 and to a lesser degree uranium-233 generates the heat needed to run nuclear reactors and provides the explosive material for nuclear weapons. Both uses rely on the ability of uranium to produce a sustained nuclear chain reaction. Depleted uranium (uranium-238) is used in kinetic energy penetrators and armor plating.
Research by Enrico Fermi and others starting in 1934 led to its use as a fuel in the nuclear power industry and in the first nuclear weapon used in war (see Little Boy and atomic bombings of Hiroshima and Nagasaki). An ensuing arms race during the Cold War between the United States and the Soviet Union produced tens of thousands of nuclear weapons that used enriched uranium and uranium-derived plutonium. The security of those weapons and their fissile material following the breakup of the Soviet Union in 1991 along with the legacy of nuclear testing and nuclear accidents is a concern for public health and safety.
History and Philosophy of Chemistry
Wikipedia:WikiProject Chemicals/Data is a collection of links and references that are useful for chemistry-related works. This includes free online chemical databases, publications, patents, computer programs, and various tools.
Science is Fun University of Wisconsin–Madison Chemistry Professor Bassam Z. Shakhashiri, shares the fun of science.
unit-conversion.info A good place to figure out what equals what.
General Chemistry Online Clear text and comprehensive coverage of general chemistry topics by Fred Senese, Dept. of Chemistry Frostburg State University
General Chemistry Demonstration at Purdue Video clips (and descriptions) of lecture demonstrations.
Intota Chemistry Experts A large online listing of real-world chemistry expert biographies provides examples of the many areas of expertise and careers in chemistry.
Chemistry Webercises Directory A large listing of chemistry resources maintained by Steven Murov, Emeritus Chemistry Professor Modesto Junior College.
MathMol MathMol (Mathematics and Molecules) is a good starting point for those interested in the field of molecular modeling.
Chemistry Educational Resources and Essential References from Wiley, the world's largest chemistry publisher
ABC-Chemistry A directory of free full-text journals in chemistry, biochemistry and related subjects.
The Element Song A goofy little song about all of the elements.
Techniques used by chemists
Equipment used by chemists
Chemistry in society
Chemistry in industry
Background color shows subcategory in the metal–metalloid–nonmetal trend:
Note: Nihonium, moscovium, tennessine, and oganesson have only recently been named.
Things you can do
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Collaboration of the Month
Every month a different chemistry-related topic, stub or non-existent article may be picked. Please improve the article any way you can.