Chemistry

For other uses, see Chemistry (disambiguation).

Chemistry (derived from alchemy) is the science of matter at or near the atomic scale. In this pursuit, chemistry deals with the structure and properties of such matter, the transformations of matter and the interactions of matter with other matter and with energy. Chemistry primarily studies atoms and collections of atoms such as molecules, crystals or metals that make up ordinary matter. According to modern chemistry it is the structure of matter at the atomic scale that is determinant of the nature of any given matter (See reductionism and quantum mechanics). It is, with physics, one of the most fundamental of all natural science.

Contents [hide] 1 Introduction 2 History of chemistry 3 Subdisciplines of chemistry 4 Fundamental concepts 4.1 Nomenclature 4.2 Atoms 4.3 Elements 4.4 Compounds 4.5 Molecules 4.6 Ions 4.7 Substance 4.8 Bonding 4.9 States of matter 4.10 Chemical reactions 4.11 Quantum chemistry 4.12 Chemical Laws 5 Etymology 6 See also 7 External links 8 Further reading 9 Reading list for university students

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Introduction

Laboratory, Institute of Biochemistry, University of Cologne

Chemistry is often called the central science because it connects other sciences, such as physics, material science, nanotechnology, biology and geology. Chemistry encompasses many specific specialized sub-disciplines that often overlap with significant portions of other sciences. Sub-disciplines, however, are very specific to chemistry, for example, they allow the manufacturing and testing of stronger materials, the synthesis of pharmaceuticals to treat disease, and determination of the mechanisms behind life processes.

A fundamental component of chemistry is that matter is involved. Chemistry may involve the interaction of matter with matter, or, involve matter with non-material phenomena such as energy. Most central and traditional to chemistry is the interaction of one substance with another such as in a chemical reaction where one substance or substances is transformed into another. This may involve electromagnetic radiation (as in photochemistry) where a chemical reaction is driven by the stimulation of light energy. However the chemical reaction is only part of a larger field that also studies matter in other ways. Chemical spectroscopists for example study the interaction of light with matter often without any reaction occurring.

Scientists who profess chemistry are known as chemists. According to contemporary chemists all ordinary matter consists of atoms or the sub atomic components that make up atoms. 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 hard because its atoms are bound together in a crystalline lattice. Wood burns because it can react spontaneously with oxygen in a chemical reaction above a certain temperature. Water is a liquid at room temperature because its molecules move about more than in a solid but less than in a gas. One can see because of the interaction of light with protein molecules in the back of ones eye.

With such a large area of study, it is impossible to know everything about chemistry and very difficult to summarize the field concisely. Even the most knowledgeable, experienced chemist only knows a very narrow area of chemistry better than others, though most chemists have a general knowledge of many areas of chemistry. Chemistry is divided into many areas of study called sub-disciplines in which chemists specialize. 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 the best solution possible is often so overwhelmingly difficult and the true solution is usually unobtainable.

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).

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History of chemistry

Linus Pauling, as a pioneer of the valence bond theory

Main article: History of chemistry

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. Alchemists discovered many chemical processes that led to the development of modern chemistry. 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 Mendeleev. The Nobel Prize in Chemistry created in 1901 gives an excellent overview of chemical discovery in the past 100 years.

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Subdisciplines of chemistry

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 subdiciplines 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. 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. In other words, it is the study of those substances that contain carbon.

• 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, Geochemistry, Green chemistry, History of chemistry, Materials science, Medicinal chemistry, Molecular Biology, Molecular genetics, Nanotechnology, Organometallic chemistry, Petrochemistry, Pharmacology, Photochemistry, Phytochemistry, Polymer chemistry, Sonochemistry, Supramolecular chemistry, Surface chemistry, and Thermochemistry.

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Fundamental concepts

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Nomenclature

Main article: IUPAC 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.

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Atoms

Main article: Atom

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.

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Elements

Main article: Chemical element

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.

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Compounds

Main article: Chemical compound

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.

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Molecules

Main article: Molecule

A molecule is the smallest indivisible portion of a pure compound or element that retains a set of unique chemical properties. A molecule consists of two or more atoms covalently bonded together.

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Ions

Main article: Ion

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⁻), or phosphate (PO₄³⁻).

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Substance

Main article: Chemical 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.

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Bonding

Electron atomic and molecular orbitals

Main article: Chemical bond

A chemical bond is an interaction 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.

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States of matter

Main article: Phase (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 is getting a lot of attention because of its relevance to biology.

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Chemical reactions

Main article: Chemical reaction

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.

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Quantum chemistry

Main article: Quantum chemistry

Quantum chemistry mathematically describes the fundamental behavior 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.

Schrödinger wave equation

In quantum mechanics (several applications in computational chemistry and quantum chemistry), the Hamiltonian 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 of a particle with no electric charge and no spin in this case is:

This is a commonly encountered form of the Schrödinger wave equation, though not the most general one. The corresponding time-independent equation is:

The relativistic generalisations of this wave equation are the Dirac equation. See Hydrogen atom for more details. Solutions of the Schrödinger equation for the hydrogen atom gives the form of the wavefunction 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 etc.

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Chemical Laws

Main article: Chemical law

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

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Etymology

Main article: Etymology of chemistry

The Etymology of the word chemistry comes directly from the Greek word χημεια, and can be also met in the old French alkemie; or the Arabic al-kimia: the art of transformation.

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See also

• List of chemists
• List of chemistry topics
• List of compounds
• List of important publications in chemistry
• Royal Society of Chemistry
• Chemistry resources
• Unsolved problems in chemistry
• Perfection ("Perfection in physics and chemistry")

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External links

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• International Union of Pure and Applied Chemistry
• IUPAC Nomenclature Home Page, see especially the "Gold Book" containing definitions of standard chemical terms
• Experiments videos and photos of the techniques and results
• More experiments - lots of information about the elements too.
• Material safety data sheets for a variety of chemicals
• Material Safety Data Sheets

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Further reading

• Chang, Raymond. Chemistry 6th ed. Boston: James M. Smith, 1998. ISBN 0071152210.
• Pauling, L. The Nature of the chemical bond (Cornell University Press) ISBN 0801403332
• Pauling, L., and Wilson, E. B. Introduction to Quantum Mechanics with Applications to Chemistry (Dover Publications) ISBN 0486648710
• Pauling, L. General Chemistry (Dover Publications) ISBN 0486656225
• Atkins, P.W. Galileo's Finger (Oxford University Press)

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Reading list for university students

• Atkins,P.W. Physical Chemistry (Oxford University Press) ISBN 0198792859
• Atkins,P.W. et al. Molecular Quantum Mechanics (Oxford University Press)
• McWeeny, R. Coulson's Valence (Oxford Science Publications) ISBN 0198551444
• Stephenson, G. Mathematical Methods for Science Students (Longman)ISBN 0582444160
• Smart and Moore Solid State Chemistry: An Introduction (Chapman and Hall) ISBN 0412400405
• Atkins,P.W., Overton,T., Rourke,J., Weller,M. and Armstrong,F. Shriver and Atkins inorganic chemistry(4th edition) 2006(Oxford University Press) ISBN 0199264635
• Clayden,J., Greeves,N., Warren,S., Wothers,P. Organic Chemistry 2000 (Oxford University Press) ISBN 0198503466
• Voet and Voet Biochemistry (Wiley) ISBN 047158651-X