Chemistry

Chemistry (from Egyptian kēme (chem), meaning "earth" See: Chemistry (etymology) for possible origins of this word. is the science concerned with the composition, structure, and properties of matter, as well as the changes it undergoes during chemical reactions. Chemistry. (n.d.). Merriam-Webster's Medical Dictionary. Retrieved August 19, 2007. Chemistry is a physical science related to studies of various atoms, molecules, crystals and other aggregates of matter whether in isolation or combination, which incorporates the concepts of energy and entropy in relation to the spontaneity of chemical processes.

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 matter; biochemistry, the study of substances found in biological organisms; physical chemistry, the energy related studies of chemical systems at macro, molecular and submolecular scales; 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 mind (see subdisciplines).

Historically, modern chemistry evolved out of alchemy following the chemical revolution (1773) (see History).

Overview

Chemistry is the scientific study of interaction of substances called chemical substances What is Chemistry? that are constituted of atoms or the subatomic components that make up atoms: protons, electrons and neutrons. Atoms combine to produce ions, molecules or crystals. Chemistry can be called "the central science" because it connects the other natural sciences, such as astronomy, physics, material science, biology, and geology. Most chemists specialize in one or more sub-disciplines.

History

The genesis of chemistry can be traced to the widely observed phenomenon of burning that led to metallurgy- the art and science of processing ores to get metals (e.g. metallurgy in ancient India). The greed for gold led to the discovery of the process for its purification, even though, the underlying principles were not well understood -- it was thought to be a transformation rather than purification. Many scholars in those days thought it reasonable to believe that there exist means for transforming cheaper (base) metals into gold. This gave way to alchemy, and the search for the Philosopher's Stone, which was believed to bring about such a transformation by mere touch.

Some consider medieval Muslims to be the earliest chemists, who introduced precise observation and controlled experimentation into the field, and discovered numerous chemical substances. Will Durant (1980), The Age of Faith (The Story of Civilization, Volume 4), p. 162-186, Simon & Schuster, ISBN 0671012002:
Template:Quote The most influential Muslim chemists were Geber (d. 815), al-Kindi (d. 873), al-Razi (d. 925), and al-Biruni (d. 1048). The works of Geber became more widely known in Europe through Latin translations by a pseudo-Geber in 14th century Spain, who also wrote some of his own books under the pen name "Geber". The contribution of Indian alchemists and metallurgists in the development of chemistry was also quite significant. Will Durant (1935): Our Oriental Heritage: Simon & Schuster:
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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. Paracelsus (1493-1541), for example, rejected the 4-elemental theory and with only a vague understanding of his chemicals and medicines, formed a hybrid of alchemy and science in what was to be called iatrochemistry. Similarly, the influences of philosophers such as Sir Francis Bacon (1561-1626) and René Descartes (1596-1650), who demanded more rigor in mathematics and in removing bias from scientific observations, led to a scientific revolution. In chemistry, this began with Robert Boyle (1627-1691), who came up with an equations known as the Boyle's Law about the characteristics of gaseous state. and later discoveries of some synthetic elements.

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 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).
• Chymistry (1661) – the subject of the material principles of mixt bodies (Boyle).
• 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).
• Chemistry (1730) – the art of resolving mixt, compound, or aggregate bodies into their principles; and of composing such bodies from those principles (Stahl).
• Chemistry (1837) – the science concerned with the laws and effects of molecular forces (Dumas).
• Chemistry (1947) – the science of substances: their structure, their properties, and the reactions that change them into other substances (Pauling).
• Chemistry (1998) – the study of matter and the changes it undergoes (Chang).

Basic concepts

Several concepts are essential for the study of chemistry, some of them are: 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').

Energy

A chemical reaction is invariably accompanied by an increase or decrease of energy of the substances involved. Some energy is transferred between the surroundings and the reactants of the reaction in the form of heat or light, thus the products of a reaction may have more or less energy than the reactants. A reaction is said to be exothermic if the final state is lower on the energy scale than the initial state; in case of endothermic reactions the situation is otherwise.

Chemical reactions are invariably not possible unless the reactants surmount an energy barrier known as the activation energy. The speed of a chemical reaction (at given temperature T) is related to the activation energy E, by the Boltzmann's population factor <math>e^{-E/kT} </math> - that is the probability of molecule to have energy greater than or equal to E at the given temperature T. This exponential dependence of a reaction rate on temperature is 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. Reilly, Michael. (2007). Mechanical force induces chemical reaction, NewScientist.com news service, Reilly

A related concept free energy, which incorporates entropy considerations too, is a very useful means for predicting the feasibility of a reaction and determining the state of equilibrium of a chemical reaction, in chemical thermodynamics. A reaction is feasible only if the total change in the Gibbs free energy is negative, <math> \Delta G \le 0 \,</math>; if it is equal to zero the chemical reaction is said to be at 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 hydrogen bonds. Whereas hydrogen sulfide (H₂S) is a gas at room temperature and standard pressure, as its molecules are bound by weaker 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 chemical substances is useful for their identification by the analysis of spectral lines of different kinds of spectra often used in chemical spectroscopy e.g. IR, microwave, NMR, ESR etc. This is used to identify the composition of remote objects - like stars and far galaxies - by analyzing their radiation (see 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

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

• Law of conservation of mass, according to the modern physics it is actually energy that is conserved, and that energy and mass are related; a concept which becomes important in nuclear chemistry.
• Law of conservation of Energy leads to the important concepts of equilibrium, thermodynamics, and kinetics.
• Law of definite composition, although in many systems (notably biomacromolecules and minerals) the ratios tend to require large numbers, and are frequently represented as a fraction.
• Law of multiple proportions
• Hess's Law
• Beer-Lambert law
• Fick's law of diffusion
• Raoult's Law
• Henry's law
• Boyle's law (1662, relating pressure and volume)
• Charles's law (1787, relating volume and temperature)
• Gay-Lussac's law (1809, relating pressure and temperature)
• Avogadro's law

Subdisciplines

Chemistry is typically divided into several major sub-disciplines. There are also several main cross-disciplinary and more specialized fields of chemistry. The Canadian Encyclopedia: Chemistry Subdisciplines [1]

• 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.

• 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, 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. Physical chemistry is a distinct discipline from chemical physics.

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

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.<ref>Template:Cite journal]

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

• 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

External links

• International Union of Pure and Applied Chemistry
• IUPAC Nomenclature Home Page, see especially the "Gold Book" containing definitions of standard chemical terms
• Interactive Mind Map of Chemistry
• / Chemical energetics