chemistry

the science of matter

the branch of the natural sciences dealing with the composition of substances and their properties and reactions the chemical composition and properties of a substance or object

"the chemistry of soil" the way two individuals relate to each other

"their chemistry was wrong from the beginning -- they hated each other"

"a mysterious alchemy brought them together"

Chemistry (derived from the Arabic word ''chemia'' (alchemy)) is the science of matter that deals with the composition, structure, and properties of chemical substancesubstances and with the chemical transformationtranformations that they undergo. In the study of matter, chemistry also investigates its interactions with energy and itself (see physics, biology). Because of the diversity of matter, which is mostly in the form of atomatoms, chemists often study how atoms of different chemical elements interact to form molecules and how molecules interact with each other.

Introduction - Chemistry is a large field encompassing many subdisciplines that often overlap with significant portions of other sciences. The fundamental component of chemistry is that it involves matter in some way (this explains its broad reach). It may involve the interaction of matter with non-material phenomena such as energy. More central to chemistry is the interaction of matter with other matter such as in the classic chemical reaction where chemical bonds are broken and made, forming new molecules.Matter, such as the chair you are sitting in or the air you breathe, is known today to consist of molecules. Each molecule consists of small bits of matter known as atoms that are connected together through chemical bonds. Each atom consists of smaller bits of matter known as subatomic particles. The structure of the world we commonly experience and the properties of the matter we commonly interact with are determined by the nature of this matter on the chemical level. Steel is hard because of how the atoms are bound together. Wood will burn because it can react with oxygen in a chemical reaction. Water is a liquid at room temperature because of how each molecule of water interacts with its neighbors. In fact, you are a thinking, sentient being because of an on-going series of chemical reactions and other chemical interactions. You can see this text because of how light interacts with molecules called proteins in the back of your eye.Chemistry is often called the central science because it is what connects most of the other sciences together. Chemistry is in some ways physics on a larger scale and in some ways is biology or geology on a smaller scale. Chemistry is used to understand and make better materials for engineering. It is used to understand the chemical mechanisms of disease as well as to create pharmaceuticals to treat disease. Chemistry is somehow involved in almost every science, every technology and every "thing".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 knowledgable, experienced chemist only knows a very narrow area of chemistry better than others. Of course, most chemists have a broad general knowledge of many areas of chemistry as well. Chemistry is divided into many areas of study called subdisciplines 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 of extraordinary utility. Chemists regularly use these simple, elegant tools and explanations in their work when they suffice 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 millenia throughout the world. The word chemistry is directly derived from the word alchemy, however the etymology of alchemy is unclear (see alchemy).

Subdisciplines of chemistry - Chemistry typically is divided into several major sub-disciplines. There are also several main cross-disciplinary and more specialized fields of chemistry.; Analytical chemistry : ''Analytical chemistry'' is the analysis of material samples to gain an understanding of their chemical composition and structure.; Biochemistry : ''Biochemistry'' is the study of the chemical compoundchemicals, chemical reactions and chemical interactions that take place in living organisms. ; Inorganic chemistry : ''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 : ''Organic chemistry'' is the study of the structure, properties, composition, mechanisms, and chemical reactionreactions of organic compounds.; Physical chemistry : ''Physical chemistry'' or ''physicochemistry'' is the study of the physical basis of chemical systems and processes. In particular, the energetic description of diverse chemical transformations are of interest to physical chemists. Important areas of study include chemical thermodynamics, chemical kinetics, statistical mechanics, and spectroscopy. Physical chemistry has large overlap with molecular physics.; Theoretical chemistry : ''Theoretical chemistry'' is the study of chemistry via 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 molecular physics. ; Other fields : Astrochemistry, Atmospheric chemistry, Chemical Engineering, Electrochemistry, Environmental chemistry, Geochemistry, History of chemistry, Materials science, Medicinal chemistry, Molecular Biology, Molecular genetics, Nuclear chemistry, Organometallic chemistry, Petrochemistry, Pharmacology, Photochemistry, Phytochemistry, Polymer chemistry, Supramolecular chemistry, Surface chemistry, and Thermochemistry.

Fundamental concepts -

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. ''See also: IUPAC nomenclature''

Atoms - ''Main article: Atom.''An ''atom'' is a collection of matter consisting of a positively charged core (the nucleus) which contains protons and neutrons, and which maintains a number of electrons to balance the positive charge in the nucleus.

Elements - ''Main article: Chemical element.''An ''element'' is a class of atoms which have the same number of protons in the atomic nucleusnucleus. 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 elements is in the periodic table, which groups elements with similar chemical properties together. Lists of the elements List of elements by nameby name, List of elements by symbolby symbol, and by List of elements by numberatomic number are also available.''See also: isotope''

Compounds - ''Main article: Chemical compound''A ''compound'' is a substance with a ''fixed ratio'' of chemical elements which determines the composition, and a particular organisation which determines chemical properties. For example, water (molecule)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 - ''Main article: Molecule.''A ''molecule'' is the smallest indivisible portion of a pure Chemical compoundcompound that retains a set of unique chemical properties. A molecule consists of two or more atoms covalently Chemical bondbonded together.

Ions - ''Main article: Ion (physics)Ion.'' An ''ion'' is a charged species, or an atom or a molecule that has lost or gained an electron. Positively charged cations (e.g. sodium cation Na⁺) and negatively charged anions (e.g. chloride Cl^-) can form neutral Saltsalts (e.g. sodium chloride NaCl). Examples of polyatomic ions that do not split up during Acid-base reaction theoriesacid-base reactions are hydroxide (OH^-), or phosphate !(PO₄< ;sup>3-).

Bonding - ''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 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 complex (chemistry) metal complexes, valence bond theory fails and alternative approaches which are based on quantum chemistry, such as molecular orbital theory, are necessary.

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 Plasma physicsplasmas, Bose-Einstein condensates and fermionic condensates and the paramagnetismparamagnetic and ferromagnetismferromagnetic 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.

Chemical reactions - ''Main article: Chemical reaction.''''Chemical reactions'' are transformations in the fine structure of molecules. 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.

Quantum chemistry - ''Main article: Quantum chemistry.''''Quantum chemistry'' describes the behavior of matter at the molecule 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 mechanics 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 atomic orbitalorbital approximation) can be understood and applied in simpler terms.

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 Einstein#Energy equivalencyrelated; a concept which becomes important in nuclear chemistry. Conservation of energy leads to the important concepts of Chemical equilibriumequilibrium, thermodynamics, and chemical kineticskinetics.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.John_DaltonDalton'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_CompoundNon-Stoichiometric CompoundsMore modern laws of chemistry define the relationship between energy and transformations.

In equilibrium, molecules exist in mixture defined by the transformations possible on the timescale of the equilibrium, and are in a ratio defined by the intrinsic energy of the molecules—the lower the intrinsic energy, the more abundant the molecule.

Transforming one structure to another requires the input of energy to cross an energy barrier; this can come from the intrinsic energy of the molecules themselves, or from an external source which will generally accelerate transformations. The higher the energy barrier, the slower the transformation occurs.

There is a hypothetical intermediate, or ''transition structure'', that corresponds to the structure at the top of the energy barrier. The Hammond-Leffler Postulate states that this structure looks most similar to the product or starting material which has intrinsic energy closest to that of the energy barrier. Stabilizing this hypothetical intermediate through chemical interaction is one way to achieve catalysis.

All chemical processes are reversible (law of microscopic reversibility) although some processes have such an energy bias, they are essentially irreversible.

History of chemistry -

Alchemy

Discovery of the chemical elements

History of chemistry

Nobel Prize in chemistry

Timeline of chemical element discovery

Etymology - Old French: ''alkemie;'' Arab ''al-kimia ''the art of transformation.'' See also: alchemy

See also -

American Chemical Society

Chemical engineering

Chemist and list of chemists

International Union of Pure and Applied Chemistry

List of chemistry topics

List of compounds

List of publications in chemistryList of important publications in chemistry

Periodic table

Chemistry resources

External links - wikibooks wikibooksparWikiversitySchool of Chemistry

allchemicals.info - Chemical Glossary

chem.sis.nlm.nih.gov - Chemistry Information Database includes basic information and some toxicity

chem.qmw.ac.uk - IUPAC Nomenclature Home Page, see especially the "Gold Book" containing definitions of standard chemical terms

cci.ethz.ch - Experiments videos and photos of the techniques and results

physchem.ox.ac.uk - Material safety data sheets for a variety of chemicals

flinnsci.com - Material Safety Data Sheets

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Primary professional organization for chemists and related occupations.
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