Chemistry



   

Chemistry (from Egyptian kēme (chem), meaning chemical processes.

Disciplines within chemistry are traditionally grouped by the type of matter being studied or the kind of study. These include neurochemistry the chemical study of the mind (see subdisciplines).

Overview

Chemistry is the scientific study of interaction of substances called material science, biology, and geology.[5][6]

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.[7]

The structure of objects we commonly use and the properties of the matter we commonly interact with, are a consequence of the properties of chemical substances and their interactions. For example, temperature; sugar and salt dissolve in water because their molecular/ionic properties are such that dissolution is preferred under the ambient conditions.

The transformations that are studied in chemistry are a result of interaction either between different chemical substances or between matter and energy. Traditional chemistry involves study of chemical equation. The number of atoms on the left and the right in the equation for a chemical transformation is most often equal. The nature 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 analysed using the tools of chemical analysis, e.g. chromatography.

Chemistry is an integral part of the science curriculum both at the high school as well as the early college level. At these levels, it is often called 'general chemistry' which is an introduction to a wide variety of fundamental concepts that enable the student to acquire tools and skills useful at the advanced levels, whereby chemistry is invariably studied in any of its various sub-disciplines. Scientists, engaged in chemical research are known as chemists.[9] Most chemists specialize in one or more sub-disciplines.

History

Main article: History of chemistry
See also: Nobel Prize in Chemistry

The genesis of chemistry can be traced to the widely observed phenomenon of burning that led to Philosopher's Stone, which was believed to bring about such a transformation by mere touch.[10]

Some consider Indian alchemists and metallurgists in the development of chemistry was also quite significant.[13]

The emergence of chemistry in Europe was primarily due to the recurrent incidence of the plague and blights there during the so called Dark Ages. This gave rise to a need for medicines. It was thought that there exists a universal medicine called the Elixir of Life that can cure all diseases, but like the Philosopher's Stone, it was never found.

For some practitioners, alchemy was an intellectual pursuit, over time, they got better at it. organic compounds, can indeed be synthesized in a chemistry laboratory also helped the modern chemistry to mature from its infancy.

The synthetic elements.

Etymology

Main article: Chemistry (etymology)

The word chemistry comes from the earlier study of alchemy, which is basically the quest to make gold from earthen starting materials.[16] As to the origin of the word "alchemy" the question is a debatable one; it certainly can be traced back to the Greeks, and some, following E. Wallis Budge, have also asserted Egyptian origins. Alchemy, generally, derives from the old French alkemie from 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 BCE – 400 BCE], formulate early "element" theories such as the Ogdoad.
  2. Greek alchemy [332 BCE – 642 CE], the Greek king Alexander the Great conquers Egypt and founds Alexandria, having the world's largest library, where scholars and wise men gather to study.
  3. Arabian alchemy [642 CE – 1200], the Arabs take over Alexandria; Jabir is the main chemist
  4. European alchemy [1300 – present], Pseudo-Geber 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".

Definitions

In retrospect, the definition of chemistry seems to invariably change per decade, as new discoveries and theories add to the functionality of the science. Shown below are some of the standard definitions used by various noted chemists:

  • Alchemy (330) – the study of the composition of waters, movement, growth, embodying and disembodying, drawing the spirits from bodies and bonding the spirits within bodies (Zosimos).[17]
  • Chymistry (1661) – the subject of the material principles of mixt bodies (Boyle).[18]
  • Chymistry (1663) – 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 an higher perfection (Glaser).[19]
  • Chemistry (1730) – the art of resolving mixt, compound, or aggregate bodies into their principles; and of composing such bodies from those principles (Stahl).[20]
  • Chemistry (1837) – the science concerned with the laws and effects of molecular forces (Dumas).[21]
  • Chemistry (1947) – the science of substances: their structure, their properties, and the reactions that change them into other substances (Pauling).[22]
  • Chemistry (1998) – the study of matter and the changes it undergoes (Chang).[23]

Basic concepts

Several concepts are essential for the study of chemistry, some of them are:[24]

Atom

Main article: Atom

An atom is the basic unit of an element. It is a collection of matter consisting of a positively charged core (the covalent.

Element

Main article: Chemical element

The concept of chemical element is related to that of chemical substance. A chemical element is characterized by a particular number of isotopes of an element, that differ from one another in the number of neutrons present in the nucleus, may exist.

The most convenient presentation of the chemical elements is in the atomic number are also available.

Compound

Main article: Chemical compound

A compound is a substance with a particular ratio of atoms of particular 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.

Substance

Main article: Chemical substance

A chemical substance is a kind of matter with a definite composition and set of properties. Strictly speaking, a mixture of compounds, elements or compounds and elements is not a chemical substance, but it may be called a chemical. Most of the substances we encounter in our daily life are some kind of mixture, e.g. biomass etc.

Nomenclature of substances is a critical part of the language of chemistry. Generally it refers to a system for naming CAS registry number.

Molecule

Main article: Molecule

A molecule is the smallest indivisible portion, beside an atom, of a pure lone pairs.   One of the main characteristic of a molecule is its geometry often called its structure. While the structure of diatomic, triatomic or tetra atomic molecules may be trivial, (linear, angular pyramidal etc.) the structure of polyatomic molecules, that are constituted of more than six atoms (of several elements) can be crucial for its chemical nature.

Mole

Main article: Mole (unit)

A mole is the amount of a molecular structures.

The number of moles of a substance in one liter of a physical chemistry.

Ions and salts

Main article: Ion

An ion is a charged species, an atom or a molecule, that has lost or gained one or more electrons. Positively charged phosphate (PO43−).

Ions in the gaseous phase is often known as plasma.

Phase

Main article: Phase (matter)

In addition to the specific chemical properties that distinguish different chemical classifications chemicals can exist in several phases. For the most part, the chemical classifications are independent of these bulk phase classifications; however, some more exotic phases are incompatible with certain chemical properties. A phase is a set of states of a chemical system that have similar bulk structural properties, over a range of conditions, such as 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 magnetic materials. 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 bond

Main article: Chemical bond

 

A chemical bond is a concept for understanding how atoms stick together in molecules. It may be visualized as the multipole balance between the positive charges in the nuclei and the negative charges oscillating about them.[28] 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 quantum chemistry such as the molecular orbital theory, are necessary. See diagram on electronic orbitals.

Chemical reaction

Main article: Chemical reaction

Chemical reaction is a concept related to the transformation of a rearrangement are some of the commonly used kinds of chemical reactions.

A chemical reaction can be symbolically depicted through a chemical equation. While in a non-nuclear chemical reaction the number and kind of atoms on both sides of the equation are equal, for a nuclear reaction this holds true only for the nuclear particles viz. protons and neutrons.[29]

The sequence of steps in which the reorganization of chemical bonds may be taking place in the course of a chemical reaction is called its Woodward-Hoffmann rules often come handy while proposing a mechanism for a chemical reaction.

A stricter definition is that "a chemical reaction is a process that results in the interconversion of chemical species".[30] Under this definition, a chemical reaction may be an 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').

Energy

Main article: Energy

A chemical reaction is invariably accompanied by an endothermic reactions the situation is otherwise.

Chemical reactions are invariably not possible unless the reactants surmount an energy barrier known as the Arrhenius equation. The activation energy necessary for a chemical reaction can be in the form of heat, light, electricity or mechanical force in the form of ultrasound.[31]

A related concept equilibrium.

There are only a limited possible states of energy for electrons, atoms and molecules. These are determined by the rules of quantum mechanics, which require quantization of energy of a bound system. The atoms/molecules in an higher energy state are said to be excited. The molecules/atoms of substance in an excited energy state are often much more reactive, that is amenable to chemical reactions.

The phase of a substance is invariably determined by its energy and those of its surroundings. When the intermolecular forces of a substance are such that energy of the surroundings is not sufficient to overcome them, it occurs in a more ordered phase like liquid or solid as is the case with water (H2O), a liquid at room temperature because its molecules are bound by dipole-dipole interactions.

The transfer of energy from one chemical substance to other depend on the size of energy quanta emitted from one substance. However, heat energy is easily transferred from almost any substance to another mainly because the vibrational and rotational energy levels in a substance are very closely placed. Because, the electronic energy levels are not so closely spaced, ultraviolet electromagnetic radiation is not transferred with equal felicity, as is also the case with electrical energy.

The existence of characteristic energy levels for different spectroscopy).

 

The term chemical energy is often used to indicate the potential of a chemical substance to undergo a transformation through a chemical reaction or transform other chemical substances.

Chemical laws

Main article: Chemical law

Chemical reactions are governed by certain laws, which have become fundamental concepts in chemistry. Some of them are:

Subdisciplines

Chemistry is typically divided into several major sub-disciplines. There are also several main cross-disciplinary and more specialized fields of chemistry.[33]

  • structure. Analytical chemistry incorporates standardized experimental methods in chemistry. These methods may be used in all subdisciplines of chemistry, excluding purely theoretical chemistry.
  • neurochemistry. Biochemistry is also associated with molecular biology and genetics.
  • 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.
  • organic compounds. An organic compound is defined as any compound based on a carbon skeleton.
  • quantum chemistry and theoretical chemistry. Physical chemistry is a distinct discipline from chemical physics.

Other fields include Thermochemistry.

Chemical industry

Main article: chemical industry

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.[34]

References

  1. ^ See: Chemistry (etymology) for possible origins of this word.
  2. ^ Chemistry. (n.d.). Merriam-Webster's Medical Dictionary. Retrieved August 19, 2007.
  3. ^ What is Chemistry?
  4. ^ Matter: Atoms from Democritus to Dalton by Anthony Carpi, Ph.D.
  5. ^ Theodore L. Brown, H. Eugene Lemay, Bruce Edward Bursten, H. Lemay. Chemistry: The Central Science. Prentice Hall; 8 edition (1999). ISBN 0130103101. Pages 3-4.
  6. ^ It is sometimes called the central science because it is seen as occupying an intermediate position in a hierarchy of the sciences by "reductive level", between physics and biology. See Carsten Reinhardt. Chemical Sciences in the 20th Century: Bridging Boundaries. Wiley-VCH, 2001. ISBN 3527302719. Pages 1-2.
  7. ^ Dictionary of the History of Ideas: Alchemy [1]
  8. ^ IUPAC Gold Book Definition
  9. ^ California Occupational Guide Number 22: Chemists[2]
  10. ^ Alchemy Timeline - Chemical Heritage Society
  11. ^ Will Durant (1980), The Age of Faith (The Story of Civilization, Volume 4), p. 162-186, Simon & Schuster, ISBN 0671012002:

    "Chemistry as a science was almost created by the Muslims; for in this field, where the Greeks (so far as we know) were confined to industrial experience and vague hypothesis, the Saracens introduced precise observation, controlled experiment, and careful records. They invented and named the alembic (al-anbiq), chemically analyzed innumerable drugs. Alchemy, which the Muslims inherited from Egypt, contributed to chemistry by a thousand incidental discoveries, and by its method, which was the most scientific of all medieval operations."

  12. ^ Dr. K. Ajram (1992), Miracle of Islamic Science, Appendix B, Knowledge House Publishers, ISBN 0911119434.

    "Humboldt regards the Muslims as the founders of chemistry."

  13. ^ Will Durant (1935): Our Oriental Heritage: Simon & Schuster:

    "Something has been said about the chemical excellence of cast iron in ancient India, and about the high industrial development of the Gupta times, when India was looked to, even by Imperial Rome, as the most skilled of the nations in such chemical industries as dyeing, tanning, soap-making, glass and cement... By the sixth century the Hindus were far ahead of Europe in industrial chemistry; they were masters of calcinations, distillation, sublimation, steaming, fixation, the production of light without heat, the mixing of anesthetic and soporific powders, and the preparation of metallic salts, compounds and alloys. The tempering of steel was brought in ancient India to a perfection unknown in Europe till our own times; King Porus is said to have selected, as a specially valuable gift from Alexander, not gold or silver, but thirty pounds of steel. The Moslems took much of this Hindu chemical science and industry to the Near East and Europe; the secret of manufacturing "Damascus" blades, for example, was taken by the Arabs from the Persians, and by the Persians from India.""

  14. ^ BBC - History - Robert Boyle (1627 - 1691)
  15. ^ Timeline of Element Discovery - About.com
  16. ^ Alchemy Lab: History of Alchemy [3]
  17. ^ Strathern, P. (2000). Mendeleyev’s Dream – the Quest for the Elements. New York: Berkley Books.
  18. ^ Boyle, Robert (1661). The Sceptical Chymist. New York: Dover Publications, Inc. (reprint). ISBN 0486428257. 
  19. ^ Glaser, Christopher (1663). Traite de la chymie.  as found in: Kim, Mi Gyung (2003). Affinity, That Elusive Dream - A Genealogy of the Chemical Revolution. The MIT Press. ISBN 0-262-11273-6. 
  20. ^ Stahl, George, E. (1730). Philosophical Principles of Universal Chemistry. 
  21. ^ Dumas, J. B. (1837). 'Affinite' (lecture notes), vii, pg 4. “Statique chimique”, Paris: Academie des Sciences
  22. ^ Pauling, Linus (1947). General Chemistry. Dover Publications, Inc.. ISBN 0486656225. 
  23. ^ Chang, Raymond (1998). Chemistry, 6th Ed.. New York: McGraw Hill. ISBN 0-07-115221-0. 
  24. ^ General Chemistry Online - Companion Notes: Matter [4]
  25. ^ IUPAC Nomenclature of Organic Chemistry [5]
  26. ^ IUPAC Provisional Recommendations for the Nomenclature of Inorganic Chemistry (2004) [6]
  27. ^ Official SI Unit definitions
  28. ^ visionlearning: Chemical Bonding by Anthony Carpi, Ph. [7]
  29. ^ Chemical Reaction Equation- IUPAC Goldbook
  30. ^ Gold Book Chemical Reaction IUPAC Goldbook
  31. ^ Reilly, Michael. (2007). Mechanical force induces chemical reaction, NewScientist.com news service, Reilly
  32. ^ Changing States of Matter - Chemforkids.com
  33. ^ The Canadian Encyclopedia: Chemistry Subdisciplines [8]
  34. ^ (July 18, 2005) "Top 50 Chemical Producers". Chemical & Engineering News 83 (29): 20–23.

Further reading

Popular reading

  • Atkins, P.W. Galileo's Finger (Oxford University Press) ISBN 0198609418
  • Atkins, P.W. Atkins' Molecules (Cambridge University Press) ISBN 0521823978
  • Stwertka, A. A Guide to the Elements (Oxford University Press) ISBN 0195150279

Introductory undergraduate text books

  • Chang, Raymond. Chemistry 6th ed. Boston: James M. Smith, 1998. ISBN 0-07-115221-0.
  • 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

Advanced undergraduate-level or graduate text books

  • 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
  • Pauling, L. The Nature of the chemical bond (Cornell University Press) ISBN 0-8014-0333-2
  • Pauling, L., and Wilson, E. B. Introduction to Quantum Mechanics with Applications to Chemistry (Dover Publications) ISBN 0-486-64871-0
  • 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

Professional societies

See also

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hak:Fa-ho̍k   This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Chemistry". A list of authors is available in Wikipedia.