Chemistry, a branch of physical science, is the study of
the composition, properties and change of matter.Chemistry is chiefly concerned
with atoms and their interactions with other atoms - for example, the
properties of the chemical bonds formed between atoms to create chemical
compounds. As well as this, interactions including atoms and other phenomena -
electrons and various forms of energy - are considered, such as photo chemical
reactions, oxidation-reduction reactions, changes in phases of matter, and
separation of mixtures. Finally, properties of matter such as alloys or
polymers are considered.
Chemistry is sometimes called "the central
science" because it bridges other natural sciences like physics, geology
and biology with each other. Chemistry is a branch of physical science but
distinct from physics.
The etymology of the word chemistry has been much
disputed. The genesis of chemistry can be traced to certain practices, known as
alchemy, which had been practiced for several millennia in various parts of the
world, particularly the Middle East.
ETYMOLOGY
The word chemistry comes from the word alchemy, an
earlier set of practices that encompassed elements of chemistry, metallurgy,
philosophy, astrology, astronomy, mysticism and medicine; it is commonly
thought of as the quest to turn lead or another common starting material into
gold.Alchemy, which was practiced around 330, is the study of the composition
of waters, movement, growth, embodying, disembodying, drawing the spirits from
bodies and bonding the spirits within bodies (Zosimos).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".
The word alchemy in turn is derived from the Persian word
kīmīa (كيميا) which is already altered into its Arabic,
al-kīmīā (الکیمیاء), form. In origin, the term is borrowed from
the Greek χημία or χημεία.This may have Egyptian origins. Many believe that
al-kīmīā is derived from χημία, which is in turn derived from the word Chemi or
Kimi, which is the ancient name of Egypt in Egyptian.Alternately, al-kīmīā may
be derived from χημεία, meaning "cast together".
DEFINITION
In retrospect, the definition of chemistry has changed
over time, as new discoveries and theories add to the functionality of the
science. The term "chymistry", in the view of noted scientist Robert
Boyle in 1661, meant the subject of the material principles of mixed bodies.In
1663, "chymistry" meant a scientific art, by which one learns to
dissolve bodies, and draw from them the different substances on their
composition, and how to unite them again, and exalt them to a higher perfection
- this definition was used by chemist Christopher Glaser.
The 1730 definition of the word "chemistry", as
used by Georg Ernst Stahl, meant the art of resolving mixed, compound, or
aggregate bodies into their principles; and of composing such bodies from those
principles.In 1837, Jean-Baptiste Dumas considered the word
"chemistry" to refer to the science concerned with the laws and effects
of molecular forces. This definition further evolved until, in 1947, it came to
mean the science of substances: their structure, their properties, and the
reactions that change them into other substances - a characterization accepted
by Linus Pauling.[More recently, in 1998, the definition of
"chemistry" was broadened to mean the study of matter and the changes
it undergoes, as phrased by Professor Raymond Chang.
HISTORY
Early civilizations, such as the Egyptians and
Babylonians amassed practical knowledge concerning the arts of metallurgy,
pottery and dyes, but didn't develop a systematic theory.
A basic chemical hypothesis first emerged in Classical
Greece with the theory of four elements as propounded definitively by
Aristotle stating that that fire, air, earth and water were the fundamental
elements from which everything is formed as a combination. Greek atomism dates
back to 440 BC, arising in works by philosophers such as Democritus and
Epicurus. In 50 BC, the Roman philosopher Lucretius expanded upon the theory in
his book De Rerum Natura (On The Nature of Things). Unlike modern concepts of
science, Greek atomism was purely philosophical in nature, with little concern
for empirical observations and no concern for chemical experiments.
In the Hellenistic world the art of alchemy first
proliferated, mingling magic and occultism into the study of natural substances
with the ultimate goal of transmuting elements into gold and discovering the
elixir of eternal life. Alchemy was discovered and practised widely throughout
the Arab world after the Muslim Conquest, and from there, diffused into
medieval and Rennaissance Europe through Latin translations.
CHEMISTRY
AS SCIENCE
Under the influence of the new empirical methods
propounded by Sir Francis Bacon and others, a group of chemists at Oxford,
Robert Boyle, Robert Hooke and John Mayow began to reshape the old achemical
traditions into a scientific discipline. Boyle in particular is regarded as the
founding father of chemistry due to his most important work, the classic
chemistry text The Sceptical Chymist where the differentiation is made between
the claims of alchemy and the empirical scientific discoveries of the new
chemistry.He formulated Boyle's law, rejected the classical "four
elements" and proposed a mechanistic alternative of atoms and chemical
reactions that could be subject to rigorous experiment.
The theory of phlogiston (a substance at the root of all
combustion) was propounded by the German Georg Ernst Stahl in the early 18th
century and was only overturned by the end of the century by the French chemist
Antoine Lavoisier, the chemical analogue of Newton in physics; who did more
than any other to establish the new science on proper theoretical footing, by
elucidating the principle of conservation of mass and developing a new system
of chemical nomenclature used to this day.
Prior to his work, though, many important discoveries had
been made, specifically relating to the nature of 'air' which was discovered to
be composed of many different gases. The Scottish chemist Joseph Black (the
first experimental chemist) and the Dutchman J. B. van Helmont discovered
carbon dioxide, or what Black called 'fixed air' in 1754; Henry Cavendish
discovered hydrogen and elucidated its' properties and Joseph Priestley and,
independently, Carl Wilhelm Scheele isolated pure oxygen.
English scientist John Dalton proposed the modern theory
of atoms in his book (1803) Atomic Theory; that all substances are composed of
indivisible 'atoms' of matter and that different atoms have varying atomic
weights.
The development of the electrochemical theory of chemical
combinations occurred in the early 19th century as the result of the work of
two scientists in particular, J. J. Berzelius and Humphry Davy, made possible
by the prior invention of the voltaic pile by Alessandro Volta. Davy discovered
nine new elements including the alkali metals by extracting them from their oxides
with electric current.
British William Prout first proposed ordering all the
elements by their atomic weight as all atoms had a weight that was an exact
multiple of the atomic weight of hydrogen. J. A. R. Newlands devised an early
table of elements, which was then developed into the modern periodic table of
elements by the German Julius Lothar Meyer and the Russian Dmitri Mendeleev in
the 1860s.The inert gases, later called the noble gases were discovered by
William Ramsay in collaboration with Lord Rayleigh at the end of the century,
thereby filling in the basic structure of the table.
Organic chemistry was developed by Justus von Liebig and
others, following Friedrich Wohler's synthesis of urea which proved that living
organisms were, in theory, reducible to chemistry. Other crucial 19th century
advances were; an understanding of valence bonding (Edward Frankland in 1852)
and the application of thermodynamics to chemistry (J. W. Gibbs and Svante
Arrhenius in the 1870s).
CHEMICAL
STRUCTURE
At the turn of the twentieth century the theoretical
underpinnings of chemistry were finally understood due to a series of
remarkable discoveries that succeeded in probing and discovering the very
nature of the internal structure of atoms. In 1897, J. J. Thomson of Cambridge
University discovered the electron and soon after the French scientist
Becquerel as well as the couple Pierre and Marie Curie investigated the
phenomenon of radioactivity. In a series of pioneering scattering experiments
Ernest Rutherford at the University of Manchester discovered the internal
structure of the atom and the existence of the proton, classified and explained
the different types of radioactivity and successfully transmuted the first
element by bombarding nitrogen with alpha particles.
His work on atomic structure was improved on by his
students, the Danish physicist Niels Bohr and Henry Mosely. The electronic
theory of chemical bonds and molecular orbitals was developed by the American
scientists Linus Pauling and Gilbert N. Lewis.
The year 2011 was declared by the United Nations as the
International Year of Chemistry.It was an initiative of the International Union
of Pure and Applied Chemistry, and of the United Nations Educational,
Scientific, and Cultural Organization and involves chemical societies,
academics, and institutions worldwide and relied on individual initiatives to
organize local and regional activities.
PRINCIPLES
OF MODERN CHEMISTRY
The current model of atomic structure is the quantum mechanical
model. Traditional chemistry starts with the study of elementary particles,
atoms, molecules, substances, metals, crystals and other aggregates of matter.
This matter can be studied in solid, liquid, or gas states, in isolation or in
combination. The interactions, reactions and transformations that are studied
in chemistry are usually the result of interactions between atoms, leading to
rearrangements of the chemical bonds which hold atoms together. Such behaviors
are studied in a chemistry laboratory.
The chemistry laboratory stereotypically uses various
forms of laboratory glassware. However glassware is not central to chemistry,
and a great deal of experimental (as well as applied/industrial) chemistry is
done without it.
A chemical reaction is a transformation of some
substances into one or more different substances.The basis of such a chemical
transformation is the rearrangement of electrons in the chemical bonds between
atoms. It can be symbolically depicted through a chemical equation, which
usually involves atoms as subjects. The number of atoms on the left and the
right in the equation for a chemical transformation is equal (when unequal, the
transformation by definition is not chemical, but rather a nuclear reaction or
radioactive decay). The type of chemical reactions a substance may undergo and
the energy changes that may accompany it are constrained by certain basic
rules, known as chemical laws.
Energy and entropy considerations are invariably
important in almost all chemical studies. Chemical substances are classified in
terms of their structure, phase, as well as their chemical compositions. They
can be analyzed using the tools of chemical analysis, e.g. spectroscopy and
chromatography. Scientists engaged in chemical research are known as chemists.
Most chemists specialize in one or more sub-disciplines. SUBDISCIPLINES
Chemistry is typically
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.
Materials Chemistry Is The Preparation,
Characterization, And Understanding Of Substances With A Useful Function. The
Field Is A New Breadth Of Study In Graduate Programs, And It Integrates
Elements From All Classical Areas Of Chemistry With A Focus On Fundamental
Issues That Are Unique To Materials. Primary Systems Of Study Include The
Chemistry Of Condensed Phases (Solids, Liquids, Polymers) And Interfaces
Between Different Phases.
Neurochemistry Is The Study Of Neurochemicals;
Including Transmitters, Peptides, Proteins, Lipids, Sugars, And Nucleic Acids;
Their Interactions, And The Roles They Play In Forming, Maintaining, And
Modifying The Nervous System.
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.
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, Spectroscopy, And
More Recently, Astrochemistry. Physical Chemistry Has Large Overlap With
Molecular Physics. Physical Chemistry Involves The Use Of Infinitesimal
Calculus In Deriving Equations. It Is Usually Associated With Quantum Chemistry
And Theoretical Chemistry. Physical Chemistry Is A Distinct Discipline From
Chemical Physics, But Again, There Is Very Strong Overlap.
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.
Other Disciplines Within Chemistry Are Traditionally
Grouped By The Type Of Matter Being Studied Or The Kind Of Study. These Include
Inorganic Chemistry, The Study Of Inorganic Matter; Organic Chemistry, The Study
Of Organic (Carbon Based) Matter; Biochemistry, The Study Of Substances Found
In Biological Organisms; Physical Chemistry, The Study Of Chemical Processes
Using Physical Concepts Such As Thermodynamics And Quantum Mechanics; And
Analytical Chemistry, The Analysis Of Material Samples To Gain An Understanding
Of Their Chemical Composition And Structure.
Many More Specialized Disciplines
Have Emerged In Recent Years, E.G. Neurochemistry The Chemical Study Of The
Nervous System Other Fields Include Agrochemistry, Astrochemistry (And
Cosmochemistry), Atmospheric Chemistry, Chemical Engineering, Chemical Biology,
Chemo-Informatics, Electrochemistry, Environmental Chemistry, Femtochemistry,
Flavor Chemistry, Flow Chemistry, Geochemistry, Green Chemistry, Histochemistry,
History Of Chemistry, Hydrogenation Chemistry, Immunochemistry, Marine
Chemistry, Materials Science, Mathematical Chemistry, Mechanochemistry,
Medicinal Chemistry, Molecular Biology, Molecular Mechanics, Nanotechnology,
Natural Product Chemistry, Oenology, Organometallic Chemistry, Petrochemistry,
Pharmacology, Photochemistry, Physical Organic Chemistry, Phytochemistry,
Polymer Chemistry, Radiochemistry, Solid-State Chemistry, Sonochemistry,
Supramolecular Chemistry, Surface Chemistry, Synthetic Chemistry,
Thermochemistry, And Many Others.
PROFESSIONAL SOCIETIES
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Branches of Chemistry
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Physical
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Chemical kinetics
Chemical physics
Electrochemistry
Femto chemistry
Geochemistry
Photochemistry
Quantum chemistry
Solid-state chemistry
Spectroscopy
Surface science
Thermochemistry
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Organic
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Biochemistry
Bioorganic chemistry
Biophysical chemistry
Chemical biology
Fullerene chemistry
Medicinal chemistry
Neurochemistry
Organic chemistry
Organometallic
chemistry
Pharmacy
Physical organic
chemistry
Polymer chemistry
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Bioinorganic chemistry
Cluster chemistry
Inorganic chemistry
Materials science
Nuclear chemistry
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Others
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Analytical chemistry
Astrochemistry
Chemistry education
Click chemistry
Computational chemistry
Cosmochemistry
Environmental chemistry
Food chemistry
Green chemistry
Supramolecular
chemistry
Theoretical chemistry
Wet chemistry
And Many More......
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