Chemistry
Chemistry (derived from
alchemy) is the
science of
matter at the
atomic to
molecular scale, dealing 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. According to modern chemistry, the physical properties of materials are generally determined by their structure at the atomic scale which is determined by the properties and energies of the interactions.
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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 study chemistry are known as
chemists. According to contemporary chemists all ordinary matter consists of
atoms or the sub atomic 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.
Water is a
liquid at room temperature because its molecules are bound by weak polar molecular interactions:
van der Waals force, which 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 tighter organized bonds to form, which requires work or
heat of fusion to disrupt, creating a solid. The organized structure actually increases the average interatomic spacing, which is why ice floats. Increasing the energy (see
heat of vaporization) enough to break the weak polar bonds at 100 degrees C, allows water to disperse enough to be a
gas. Note in each case, there is energy required to break the bonds, and more energy to move the molecules away from each other.
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).
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.
The
chemical industry represents an important economic activity. The global top 50 chemical producers in 2004 has sales of 587 billion
dollars with a profit margin of 8.1% and
research and development spending of 2.1% both against sales.
Chemistry typically is divided into several major sub-disciplines. There are also several main cross-disciplinary and more specialized fields of chemistry.
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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.
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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.
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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.
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Organic chemistry is the study of the structure, properties, composition, mechanisms, and
reactions of
organic compounds. An organic compound is formally defined as any compound bearing one or more covalent bonds between two or more carbon atoms.
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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.
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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.
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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.
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.
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
-), or
phosphate (PO
43-).
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.
Bonding
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.
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.
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.
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 of a particle with no
electric charge and no
spin is described by the
Schrödinger wave equation.
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.
Main article: Etymology of chemistry
The word chemistry comes from the
Greek word
chemeia (χημεία) meaning "cast together", "pour together", "weld", "alloy", etc. (from
khumatos, "that which is poured out, an ingot", or from
Persian Kimia meaning "gold." It can be also met in the old French
alkemie; or the Arabic
al-kimia: the art of transformation.*
List of chemistry topics*
List of chemists*
List of compounds*
List of important publications in chemistry*
Perfection (
"Perfection in physics and chemistry")
*
Royal Society of Chemistry*
Unsolved problems in chemistry*
Chemie-Wereld: Startpage (chemistry-world)*
MIT OpenCourseWare | Chemistry*
Chemportal - The navigator for the slovak and czech chemical industry (slovak)*
Wikidchem, The Free Chemistry Archive Wiki*
Chemical Glossary*
Chemical Portal*
Chemistry Information Database*
Chemistry Forum*
Chemistry Guide*
Chemistry Research*
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*
Chemical BlogsFor a full list of external links and suppliers see
Wikipedia:Chemical sources* 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)
*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
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