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Chemistry

2007 Schools Wikipedia Selection. Related subjects: General Chemistry

   Chemistry (from Greek χημεία khemeia meaning "alchemy") is the science
   of matter at the atomic to molecular scale, dealing primarily with
   collections of atoms, such as molecules, crystals, and metals.
   Chemistry deals with the composition and statistical properties of such
   structures, as well as their transformations and interactions to become
   materials encountered in everyday life. Chemistry also deals with
   understanding the properties and interactions of individual atoms with
   the purpose of applying that knowledge at the macroscopic level.
   According to modern chemistry, the physical properties of materials are
   generally determined by their structure at the atomic scale, which is
   itself defined by interatomic forces.
   Chemistry - the study of atoms and the structures they unite to form
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   Chemistry - the study of atoms and the structures they unite to form

Introduction

   Chemistry is often called the "central science" because it connects
   other sciences, such as physics, material science, nanotechnology,
   biology, pharmacy, medicine, bioinformatics, and geology. These
   connections are formed through various sub-disciplines that utilize
   concepts from multiple scientific disciplines. For example, physical
   chemistry involves applying the principles of physics to materials at
   the atomic and molecular level.

   Chemistry pertains to the interactions of matter. These interactions
   may be between two material substances or between matter and energy,
   especially in conjunction with the First Law of Thermodynamics.
   Traditional chemistry involves interactions between substances in
   chemical reactions, where one or more substances become one or more
   other substances. Sometimes these reactions are driven by energetic
   (enthalpic) considerations, such as when two highly energetic
   substances such as elemental hydrogen and oxygen react to form the less
   energetic substance water. Chemical reactions may be facilitated by a
   catalyst, which is generally another chemical substance present within
   the reaction media but unconsumed (such as sulfuric acid catalyzing the
   electrolysis of water) or a non-material phenomenon (such as
   electromagnetic radiation in photochemical reactions). Traditional
   chemistry also deals with the analysis of chemicals both in and apart
   from a reaction, as in spectroscopy.
   Laboratory, Institute of Biochemistry, University of Cologne
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   Laboratory, Institute of Biochemistry, University of Cologne

   All ordinary matter consists of atoms or the subatomic components that
   make up atoms; protons, electrons and neutrons. Atoms may be combined
   to produce more complex forms of matter such as ions, molecules or
   crystals. The structure of the world we commonly experience and the
   properties of the matter we commonly interact with are determined by
   properties of chemical substances and their interactions. Steel is
   harder than iron because its atoms are bound together in a more rigid
   crystalline lattice. Wood burns or undergoes rapid oxidation because it
   can react spontaneously with oxygen in a chemical reaction above a
   certain temperature.

   Substances tend to be classified in terms of their energy or phase as
   well as their chemical compositions. The three phases of matter at low
   energy are Solid, Liquid and Gas. Solids have fixed structures at room
   temperature which can resist gravity and other weak forces attempting
   to rearrange them, due to their tight bonds. Liquids have limited
   bonds, with no structure and flow with gravity. Gases have no bonds and
   act as free particles. Another way to view the three phases is by
   volume and shape: roughly speaking, solids have fixed volume and shape,
   liquids have fixed volume but no fixed shape, and gases have neither
   fixed volume nor fixed shape.

   Water (H[2]O) is a liquid at room temperature because its molecules are
   bound by intermolecular forces called Hydrogen bonds. Hydrogen sulfide
   (H[2]S) on the other hand is a gas at room temperature and standard
   pressure, as its molecules are bound by weaker dipole-dipole
   interactions. The hydrogen bonds in water have enough energy to keep
   the water molecules from separating from each other but not from
   sliding around, making it a liquid at temperatures between 0 ° C and
   100 °C at sea level. Lowering the temperature or energy further, allows
   for a tighter organization to form, creating a solid, and releasing
   energy. Increasing the energy (see heat of fusion) will melt the ice
   although the temperature will not change until all the ice is melted.
   Increasing the temperature of the water will eventually cause boiling
   (see heat of vaporization) when there is enough energy to overcome the
   polar attractions between individual water molecules (100 °C at 1
   atmosphere of pressure), allowing the H[2]O molecules to disperse
   enough to be a gas. Note that in each case there is energy required to
   overcome the intermolecular attractions and thus allow the molecules to
   move away from each other.

   Scientists who study chemistry are known as chemists. Most chemists
   specialize in one or more sub-disciplines. The chemistry taught at the
   high school or early college level is often called "general chemistry"
   and is intended to be an introduction to a wide variety of fundamental
   concepts and to give the student the tools to continue on to more
   advanced subjects. Many concepts presented at this level are often
   incomplete and technically inaccurate, yet they are of extraordinary
   utility. Chemists regularly use these simple, elegant tools and
   explanations in their work because they have been proven to accurately
   model a very wide array of chemical reactivity, are generally
   sufficient, and more precise solutions may be prohibitively difficult
   to obtain.

   The science of chemistry is historically a recent development but has
   its roots in alchemy which has been practiced for millennia throughout
   the world. The word chemistry is directly derived from the word
   alchemy; however, the etymology of alchemy is unclear (see alchemy).

History of chemistry

   Robert Boyle - founder of modern chemistry through use of controlled
   experiments, as contrasted with earlier rudimentary alchemical methods
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   Robert Boyle - founder of modern chemistry through use of controlled
   experiments, as contrasted with earlier rudimentary alchemical methods

   .

   The roots of chemistry can be traced to the phenomenon of burning. Fire
   was a mystical force that transformed one substance into another and
   thus was of primary interest to mankind. It was fire that led to the
   discovery of iron and glass. After gold was discovered and became a
   precious metal, many people were interested to find a method that could
   convert other substances into gold. This led to the protoscience called
   Alchemy. Alchemy was practiced by many cultures throughout history and
   often contained a mixture of philosophy, mysticism, and protoscience
   (see Alchemy).

   Alchemists discovered many chemical processes that led to the
   development of modern chemistry. As history progressed the more notable
   alchemists (esp. Geber and Paracelsus) evolved alchemy away from
   philosophy and mysticism and developed more systematic and scientific
   approaches. The first alchemist considered to apply the scientific
   method to alchemy and to distinguish chemistry from alchemy was Robert
   Boyle (1627–1691); however, chemistry as we know it today was invented
   by Antoine Lavoisier with his law of Conservation of mass in 1783. The
   discoveries of the chemical elements has a long history culminating in
   the creation of the periodic table of the chemical elements by Dmitri
   Mendeleyev.

   The Nobel Prize in Chemistry created in 1901 gives an excellent
   overview of chemical discovery in the past 100 years. In the early part
   of the 20th century the subatomic nature of atoms were revealed and the
   science of quantum mechanics began to explain the physical nature of
   the chemical bond. By the mid 20th century chemistry had developed to
   the point of being able to understand and predict aspects of biology
   spawning the field of biochemistry.

   The chemical industry represents an important economic activity. The
   global top 50 chemical producers in 2004 had sales of 587 billion US
   dollars with a profit margin of 8.1% and research and development
   spending of 2.1% of total chemical sales.

Subdisciplines of chemistry

   Lab pipettes
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   Lab pipettes

   Chemistry typically is divided into several major sub-disciplines.
   There are also several main cross-disciplinary and more specialized
   fields of chemistry.
     * Analytical chemistry is the analysis of material samples to gain an
       understanding of their chemical composition and structure.
       Analytical chemistry incorporates standardized experimental methods
       in chemistry. These methods may be used in all subdisciplines of
       chemistry, excluding purely theoretical chemistry.

     * Biochemistry is the study of the chemicals, chemical reactions and
       chemical interactions that take place in living organisms.
       Biochemistry and organic chemistry are closely related, as in
       medicinal chemistry or neurochemistry. Biochemistry is also
       associated with molecular biology and genetics.

     * Inorganic chemistry is the study of the properties and reactions of
       inorganic compounds. The distinction between organic and inorganic
       disciplines is not absolute and there is much overlap, most
       importantly in the sub-discipline of organometallic chemistry.

     * Organic chemistry is the study of the structure, properties,
       composition, mechanisms, and reactions of organic compounds. An
       organic compound is defined as any compound based on a carbon
       skeleton.

     * Physical chemistry is the study of the physical and fundamental
       basis of chemical systems and processes. In particular, the
       energetics and dynamics of such systems and processes are of
       interest to physical chemists. Important areas of study include
       chemical thermodynamics, chemical kinetics, electrochemistry,
       statistical mechanics, and spectroscopy. Physical chemistry has
       large overlap with molecular physics. Physical chemistry involves
       the use of calculus in deriving equations. It is usually associated
       with quantum chemistry and theoretical chemistry.

     * Theoretical chemistry is the study of chemistry via fundamental
       theoretical reasoning (usually within mathematics or physics). In
       particular the application of quantum mechanics to chemistry is
       called quantum chemistry. Since the end of the Second World War,
       the development of computers has allowed a systematic development
       of computational chemistry, which is the art of developing and
       applying computer programs for solving chemical problems.
       Theoretical chemistry has large overlap with (theoretical and
       experimental) condensed matter physics and molecular physics.
       Essentially from reductionism theoretical chemistry is just
       physics, just like fundamental biology is just chemistry and
       physics.

     * Nuclear chemistry is the study of how subatomic particles come
       together and make nuclei. Modern Transmutation is a large component
       of nuclear chemistry, and the table of nuclides is an important
       result and tool for this field.

   Other fields include Astrochemistry, Atmospheric chemistry, Chemical
   Engineering, Chemo-informatics, Electrochemistry, Environmental
   chemistry, Flow chemistry, Geochemistry, Green chemistry, History of
   chemistry, Materials science, Medicinal chemistry, Molecular Biology,
   Molecular genetics, Nanotechnology, Organometallic chemistry,
   Petrochemistry, Pharmacology, Photochemistry, Phytochemistry, Polymer
   chemistry, Solid-state chemistry, Sonochemistry, Supramolecular
   chemistry, Surface chemistry, and Thermochemistry.

Fundamental concepts

Nomenclature

   Nomenclature refers to the system for naming chemical compounds. There
   are well-defined systems in place for naming chemical species. Organic
   compounds are named according to the organic nomenclature system.
   Inorganic compounds are named according to the inorganic nomenclature
   system.

Atoms

   An atom is a collection of matter consisting of a positively charged
   core (the atomic nucleus) which contains protons and neutrons, and
   which maintains a number of electrons to balance the positive charge in
   the nucleus. The Atom is also the smallest portion into which an
   element can be divided and still retain its properties, made up of a
   dense, positively charged nucleus surrounded by a system of electrons.

Elements

   An element is a class of atoms which have the same number of protons in
   the nucleus. This number is known as the atomic number of the element.
   For example, all atoms with 6 protons in their nuclei are atoms of the
   chemical element carbon, and all atoms with 92 protons in their nuclei
   are atoms of the element uranium.

   The most convenient presentation of the chemical elements is in the
   periodic table of the chemical elements, which groups elements by
   atomic number. Due to its ingenious arrangement, groups, or columns,
   and periods, or rows, of elements in the table either share several
   chemical properties, or follow a certain trend in characteristics such
   as atomic radius, electronegativity, electron affinity, and etc. Lists
   of the elements by name, by symbol, and by atomic number are also
   available. In addition, several isotopes of an element may exist.

Ions

   An ion is a charged species, or an atom or a molecule that has lost or
   gained one or more electrons. Positively charged cations (e.g. sodium
   cation Na^+) and negatively charged anions (e.g. chloride Cl^−) can
   form neutral salts (e.g. sodium chloride NaCl). Examples of polyatomic
   ions that do not split up during acid-base reactions are hydroxide
   (OH^−) and phosphate (PO[4]^3−).

Compounds

   A compound is a substance with a fixed ratio of chemical elements which
   determines the composition, and a particular organization which
   determines chemical properties. For example, water is a compound
   containing hydrogen and oxygen in the ratio of two to one, with the
   oxygen between the hydrogens, and an angle of 104.5° between them.
   Compounds are formed and interconverted by chemical reactions.

Molecules

   A molecule is the smallest indivisible portion of a pure compound or
   element that retains a set of unique chemical properties.

Substance

   A chemical substance can be an element, compound or a mixture of
   compounds, elements or compounds and elements. Most of the matter we
   encounter in our daily life are one or another kind of mixtures, e.g.
   air, alloys, biomass etc.gg6tgvygyhgygtgfedtgffted

Bonding

   Electron atomic and molecular orbitals
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   Electron atomic and molecular orbitals

   A chemical bond is the multipole balance between the positive charges
   in the nuclei and the negative charges oscillating about them. More
   than simple attraction and repulsion, the energies and distributions
   characterize the availability of an electron to bond to another atom.
   These potentials create the interactions which holds together atoms in
   molecules or crystals. In many simple compounds, Valence Bond Theory,
   the Valence Shell Electron Pair Repulsion model ( VSEPR), and the
   concept of oxidation number can be used to predict molecular structure
   and composition. Similarly, theories from classical physics can be used
   to predict many ionic structures. With more complicated compounds, such
   as metal complexes, valence bond theory fails and alternative
   approaches, primarily based on principles of quantum chemistry such as
   the molecular orbital theory, are necessary. See diagram on electronic
   orbitals.

States of matter

   A phase is a set of states of a chemical system that have similar bulk
   structural properties, over a range of conditions, such as pressure or
   temperature. Physical properties, such as density and refractive index
   tend to fall within values characteristic of the phase. The phase of
   matter is defined by the phase transition, which is when energy put
   into or taken out of the system goes into rearranging the structure of
   the system, instead of changing the bulk conditions.

   Sometimes the distinction between phases can be continuous instead of
   having a discrete boundary, in this case the matter is considered to be
   in a supercritical state. When three states meet based on the
   conditions, it is known as a triple point and since this is invariant,
   it is a convenient way to define a set of conditions.

   The most familiar examples of phases are solids, liquids, and gases.
   Less familiar phases include plasmas, Bose-Einstein condensates and
   fermionic condensates and the paramagnetic and ferromagnetic phases of
   magnetic materials. Even the familiar ice has many different phases,
   depending on the pressure and temperature of the system. While most
   familiar phases deal with three-dimensional systems, it is also
   possible to define analogs in two-dimensional systems, which has
   received attention for its relevance to systems in biology.

Chemical reactions

   A Chemical reaction is a process that results in the interconversion of
   chemical substances. Such reactions can result in molecules attaching
   to each other to form larger molecules, molecules breaking apart to
   form two or more smaller molecules, or rearrangement of atoms within or
   across molecules. Chemical reactions usually involve the making or
   breaking of chemical bonds. For example, substances that react with
   oxygen to produce other substances are said to undergo oxidation;
   similarly a group of substances called acids or alkalis can react with
   one another to neutralize each other's effect, a phenomenon known as
   neutralization. Substances can also be dissociated or synthesized from
   other substances by various different chemical processes.

   A stricter definition exists that states "a Chemical Reaction is a
   process that results in the interconversion of chemical species". Under
   this definition, a chemical reaction may be an elementary reaction or a
   stepwise reaction. An additional caveat is made, in that this
   definition includes cases where the interconversion of conformers is
   experimentally observable. Such detectable chemical reactions normally
   involve sets of molecular entities as indicated by this definition, but
   it is often conceptually convenient to use the term also for changes
   involving single molecular entities (i.e. 'microscopic chemical
   events').

Quantum chemistry

   Quantum chemistry mathematically describes the fundamental behaviour of
   matter at the molecular scale. It is, in principle, possible to
   describe all chemical systems using this theory. In practice, only the
   simplest chemical systems may realistically be investigated in purely
   quantum mechanical terms, and approximations must be made for most
   practical purposes (e.g., Hartree-Fock, post Hartree-Fock or Density
   functional theory, see computational chemistry for more details). Hence
   a detailed understanding of quantum mechanics is not necessary for most
   chemistry, as the important implications of the theory (principally the
   orbital approximation) can be understood and applied in simpler terms.

   In quantum mechanics (several applications in computational chemistry
   and quantum chemistry), the Hamiltonian, or the physical state, of a
   particle can be expressed as the sum of two operators, one
   corresponding to kinetic energy and the other to potential energy. The
   Hamiltonian in the Schrödinger wave equation used in quantum chemistry
   does not contain terms for the spin of the electron.

   Solutions of the Schrödinger equation for the hydrogen atom gives the
   form of the wave function for atomic orbitals, and the relative energy
   of say the 1s,2s,2p and 3s orbitals. The orbital approximation can be
   used to understand the other atoms e.g. helium, lithium and carbon.

Chemical Laws

   The most fundamental concept in chemistry is the law of conservation of
   mass, which states that there is no detectable change in the quantity
   of matter during an ordinary chemical reaction. Modern physics shows
   that it is actually energy that is conserved, and that energy and mass
   are related; a concept which becomes important in nuclear chemistry.
   Conservation of energy leads to the important concepts of equilibrium,
   thermodynamics, and kinetics.

   Further laws of chemistry elaborate on the law of conservation of mass.
   Joseph Proust's law of definite composition says that pure chemicals
   are composed of elements in a definite formulation; we now know that
   the structural arrangement of these elements is also important.

   Dalton's law of multiple proportions says that these chemicals will
   present themselves in proportions that are small whole numbers (i.e.
   1:2 O:H in water); although in many systems (notably biomacromolecules
   and minerals) the ratios tend to require large numbers, and are
   frequently represented as a fraction. Such compounds are known as
   non-stoichiometric compounds.

Chemistry societies

     * American Chemical Society
     * Chemical Institute of Canada
     * Chemical Society of Peru
     * International Union of Pure and Applied Chemistry
     * Royal Australian Chemical Institute
     * Royal Society of Chemistry
     * Society of Chemical Industry
     * World Association of Theoretical and Computational Chemists

Interpersonal chemistry

   In the fields of sociology, behavioural psychology, and evolutionary
   psychology, with specific reference to intimate relationships or
   romantic relationships, interpersonal chemistry is a reaction between
   two people or the spontaneous reaction of two people to each other,
   especially a mutual sense of attraction or understanding. In a
   colloquial sense, it is often intuited that people can have either good
   chemistry or bad chemistry together. Other related terms are team
   chemistry, a phrase often used in sports, and business chemistry, as
   between two companies. Recent developments in neurochemistry have begun
   to shed light on the nature of the "chemistry of love", in terms of
   measurable changes neurotransmitters such as oxytocin, serotonin, and
   dopamine.

Etymology

   The word chemistry comes from the earlier study of alchemy, which is
   basically the quest to make gold from earthen starting materials. As to
   the origin of the word “alchemy” the question is a debatable one; it
   certainly has Greek origins, and some, following E. Wallis Budge, have
   also asserted Egyptian origins. Alchemy, generally, derives from the
   old French alkemie; and the Arabic al-kimia: "the art of
   transformation." The Arabs borrowed the word “kimia” from the Greeks
   when they conquered Alexandria in the year 642 AD. A tentative outline
   is as follows:
    1. Egyptian alchemy [5,000 BC – 400 BC], Alexandria has the world’s
       largest library
    2. Greek alchemy [332 BC – 642 AD], the Greeks take over Alexandria
    3. Arabian alchemy [642 AD – 1200], the Arabs take over Alexandria,
       e.g. Jabir is the main chemist.
    4. European alchemy [1300 – Present], Gerber builds on Arabic
       chemistry
    5. Chemistry [1661], Boyle writes his classic chemistry text The
       Sceptical Chymist
    6. Chemistry [1787], Lavoisier writes his classic Elements of
       Chemistry
    7. Chemistry [1803], Dalton publishes his Atomic Theory

   Thus, an alchemist was called a 'chemist' in popular speech, and later
   the suffix "-ry" was added to this to describe the art of the chemist
   as "chemistry".

Reading list for university students

     * Atkins,P.W. Physical Chemistry (Oxford University Press) ISBN
       0-19-879285-9
     * Atkins,P.W. et al. Molecular Quantum Mechanics (Oxford University
       Press)
     * McWeeny, R. Coulson's Valence (Oxford Science Publications) ISBN
       0-19-855144-4
     * Stephenson, G. Mathematical Methods for Science Students (Longman)
       ISBN 0-582-44416-0
     * Smart and Moore Solid State Chemistry: An Introduction (Chapman and
       Hall) ISBN 0-412-40040-5
     * Atkins,P.W., Overton,T., Rourke,J., Weller,M. and Armstrong,F.
       Shriver and Atkins inorganic chemistry(4th edition) 2006(Oxford
       University Press) ISBN 0-19-926463-5
     * Clayden,J., Greeves,N., Warren,S., Wothers,P. Organic Chemistry
       2000 (Oxford University Press) ISBN 0-19-850346-6
     * Voet and Voet Biochemistry (Wiley) ISBN 0-471-58651-X

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