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Chemistry
Chemistry
is the scientific discipline involved with compounds composed of atoms, i.e. elements, and molecules, i.e. combinations of atoms: their composition, structure, properties, behavior and the changes they undergo during a reaction with other compounds.[1][2] Chemistry
Chemistry
addresses topics such as how atoms and molecules interact via chemical bonds to form new chemical compounds. There are four types of chemical bonds: covalent bonds, in which compounds share one or more electron(s); ionic bonds, in which a compound donates one or more electrons to another compound to produce ions: cations and anions; hydrogen bonds; and Van der Waals force
Van der Waals force
bonds. See glossary of chemistry. In the scope of its subject, chemistry occupies an intermediate position between physics and biology.[3] It is sometimes called the central science because it provides a foundation for understanding both basic and applied scientific disciplines at a fundamental level.[4] Examples include plant chemistry (botany), the formation of igneous rocks (geology), how atmospheric ozone is formed and how environmental pollutants are degraded (ecology), the properties of the soil on the moon (astrophysics), how medications work (pharmacology), and how to collect DNA evidence at a crime scene (forensics). The history of chemistry spans a period from very old times to the present. Since several millennia BC, civilizations were using technologies that would eventually form the basis of the various branches of chemistry. Examples include extracting metals from ores, making pottery and glazes, fermenting beer and wine, extracting chemicals from plants for medicine and perfume, rendering fat into soap, making glass, and making alloys like bronze. Chemistry
Chemistry
was preceded by its protoscience, alchemy, which is an intuitive but non-scientific approach to understanding the constituents of matter and their interactions. It was unsuccessful in explaining the nature of matter and its transformations, but, by performing experiments and recording the results, alchemists set the stage for modern chemistry. Chemistry
Chemistry
as a body of knowledge distinct from alchemy began to emerge when a clear differentiation was made between them by Robert Boyle
Robert Boyle
in his work The Sceptical Chymist
The Sceptical Chymist
(1661). While both alchemy and chemistry are concerned with matter and its transformations, the crucial difference was given by the scientific method that chemists employed in their work. Chemistry
Chemistry
is considered to have become an established science with the work of Antoine Lavoisier, who developed a law of conservation of mass that demanded careful measurement and quantitative observations of chemical phenomena. The history of chemistry is intertwined with the history of thermodynamics, especially through the work of Willard Gibbs.[5]

Contents

1 Etymology 2 Modern principles

2.1 Matter

2.1.1 Atom 2.1.2 Element 2.1.3 Compound 2.1.4 Molecule 2.1.5 Substance and mixture 2.1.6 Mole and amount of substance

2.2 Phase 2.3 Bonding 2.4 Energy 2.5 Reaction 2.6 Ions and salts 2.7 Acidity and basicity 2.8 Redox 2.9 Equilibrium 2.10 Chemical laws

3 History

3.1 Of definition 3.2 Of discipline

4 Practice

4.1 Subdisciplines 4.2 Industry 4.3 Professional societies

5 See also 6 References 7 Bibliography 8 Further reading 9 External links

Etymology The word chemistry comes from alchemy, which referred to an earlier set of practices that encompassed elements of chemistry, metallurgy, philosophy, astrology, astronomy, mysticism and medicine. It is often seen as linked to the quest to turn lead or another common starting material into gold,[6] though in ancient times the study encompassed many of the questions of modern chemistry being defined as the study of the composition of waters, movement, growth, embodying, disembodying, drawing the spirits from bodies and bonding the spirits within bodies by the early 4th century Greek-Egyptian alchemist Zosimos.[7] 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". The modern word alchemy in turn is derived from the Arabic word al-kīmīā (الكیمیاء). In origin, the term is borrowed from the Greek χημία or χημεία.[8][9] This may have Egyptian origins since al-kīmīā is derived from the Greek χημία, which is in turn derived from the word Kemet, which is the ancient name of Egypt
Egypt
in Egyptian.[8] Alternately, al-kīmīā may derive from χημεία, meaning "cast together".[10] Modern principles

Laboratory, Institute of Biochemistry, University of Cologne
University of Cologne
in Germany.

The current model of atomic structure is the quantum mechanical model.[11] Traditional chemistry starts with the study of elementary particles, atoms, molecules,[12] substances, metals, crystals and other aggregates of matter. This matter can be studied in solid, liquid, or gas states, in isolation or in combination. The interactions, reactions and transformations that are studied in chemistry are usually the result of interactions between atoms, leading to rearrangements of the chemical bonds which hold atoms together. Such behaviors are studied in a chemistry laboratory. The chemistry laboratory stereotypically uses various forms of laboratory glassware. However glassware is not central to chemistry, and a great deal of experimental (as well as applied/industrial) chemistry is done without it.

Solutions of substances in reagent bottles, including ammonium hydroxide and nitric acid, illuminated in different colors

A chemical reaction is a transformation of some substances into one or more different substances.[13] The basis of such a chemical transformation is the rearrangement of electrons in the chemical bonds between atoms. It can be symbolically depicted through a chemical equation, which usually involves atoms as subjects. The number of atoms on the left and the right in the equation for a chemical transformation is equal. (When the number of atoms on either side is unequal, the transformation is referred to as a nuclear reaction or radioactive decay.) The type 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
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 analyzed using the tools of chemical analysis, e.g. spectroscopy and chromatography. Scientists engaged in chemical research are known as chemists.[14] Most chemists specialize in one or more sub-disciplines. Several concepts are essential for the study of chemistry; some of them are:[15] Matter Main article: Matter In chemistry, matter is defined as anything that has rest mass and volume (it takes up space) and is made up of particles. The particles that make up matter have rest mass as well – not all particles have rest mass, such as the photon. Matter
Matter
can be a pure chemical substance or a mixture of substances.[16] Atom Main article: Atom

A diagram of an atom based on the Bohr model

The atom is the basic unit of chemistry. It consists of a dense core called the atomic nucleus surrounded by a space hosting an electron cloud. The nucleus is made up of positively charged protons and uncharged neutrons (together called nucleons), while the electron cloud consists of negatively charged electrons which orbit the nucleus. In a neutral atom, the negatively charged electrons balance out the positive charge of the protons. The nucleus is dense; the mass of a nucleon is appromixately 1,836 times that of an electron, yet the radius of an atom is about 10,000 times that of its nucleus.[17][18] The atom is also the smallest entity that can be envisaged to retain the chemical properties of the element, such as electronegativity, ionization potential, preferred oxidation state(s), coordination number, and preferred types of bonds to form (e.g., metallic, ionic, covalent). Element

Standard form of the periodic table of chemical elements. The colors represent different categories of elements

Main article: Chemical element A chemical element is a pure substance which is composed of a single type of atom, characterized by its particular number of protons in the nuclei of its atoms, known as the atomic number and represented by the symbol Z. The mass number is the sum of the number of protons and neutrons in a nucleus. Although all the nuclei of all atoms belonging to one element will have the same atomic number, they may not necessarily have the same mass number; atoms of an element which have different mass numbers are known as isotopes. For example, all atoms with 6 protons in their nuclei are atoms of the chemical element carbon, but atoms of carbon may have mass numbers of 12 or 13.[18] The standard presentation of the chemical elements is in the periodic table, which orders elements by atomic number. The periodic table is arranged in groups, or columns, and periods, or rows. The periodic table is useful in identifying periodic trends.[19] Compound

Carbon
Carbon
dioxide (CO2), an example of a chemical compound

Main article: Chemical compound A compound is a pure chemical substance composed of more than one element. The properties of a compound bear little similarity to those of its elements.[20] The standard nomenclature of compounds is set by the International Union of Pure and Applied Chemistry
International Union of Pure and Applied Chemistry
(IUPAC). Organic compounds are named according to the organic nomenclature system.[21] The names for Inorganic compounds are created according to the inorganic nomenclature system. When a compound has more than one component, then they are divided into two classes, the electropositive and the electronegative components.[22] In addition the Chemical Abstracts Service has devised a method to index chemical substances. In this scheme each chemical substance is identifiable by a number known as its CAS registry number. Molecule Main article: Molecule

A ball-and-stick representation of the caffeine molecule (C8H10N4O2).

A molecule is the smallest indivisible portion of a pure chemical substance that has its unique set of chemical properties, that is, its potential to undergo a certain set of chemical reactions with other substances. However, this definition only works well for substances that are composed of molecules, which is not true of many substances (see below). Molecules
Molecules
are typically a set of atoms bound together by covalent bonds, such that the structure is electrically neutral and all valence electrons are paired with other electrons either in bonds or in lone pairs. Thus, molecules exist as electrically neutral units, unlike ions. When this rule is broken, giving the "molecule" a charge, the result is sometimes named a molecular ion or a polyatomic ion. However, the discrete and separate nature of the molecular concept usually requires that molecular ions be present only in well-separated form, such as a directed beam in a vacuum in a mass spectrometer. Charged polyatomic collections residing in solids (for example, common sulfate or nitrate ions) are generally not considered "molecules" in chemistry. Some molecules contain one or more unpaired electrons, creating radicals. Most radicals are comparatively reactive, but some, such as nitric oxide (NO) can be stable.

A 2-D skeletal model of a benzene molecule (C6H6)

The "inert" or noble gas elements (helium, neon, argon, krypton, xenon and radon) are composed of lone atoms as their smallest discrete unit, but the other isolated chemical elements consist of either molecules or networks of atoms bonded to each other in some way. Identifiable molecules compose familiar substances such as water, air, and many organic compounds like alcohol, sugar, gasoline, and the various pharmaceuticals. However, not all substances or chemical compounds consist of discrete molecules, and indeed most of the solid substances that make up the solid crust, mantle, and core of the Earth are chemical compounds without molecules. These other types of substances, such as ionic compounds and network solids, are organized in such a way as to lack the existence of identifiable molecules per se. Instead, these substances are discussed in terms of formula units or unit cells as the smallest repeating structure within the substance. Examples of such substances are mineral salts (such as table salt), solids like carbon and diamond, metals, and familiar silica and silicate minerals such as quartz and granite. One of the main characteristics 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. Substance and mixture

Examples of pure chemical substances. From left to right: the elements tin (Sn) and sulfur (S), diamond (an allotrope of carbon), sucrose (pure sugar), and sodium chloride (salt) and sodium bicarbonate (baking soda), which are both ionic compounds.

A chemical substance is a kind of matter with a definite composition and set of properties.[23] A collection of substances is called a mixture. Examples of mixtures are air and alloys.[24] Mole and amount of substance Main article: Mole The mole is a unit of measurement that denotes an amount of substance (also called chemical amount). The mole is defined as the number of atoms found in exactly 0.012 kilogram (or 12 grams) of carbon-12, where the carbon-12 atoms are unbound, at rest and in their ground state.[25] The number of entities per mole is known as the Avogadro constant, and is determined empirically to be approximately 6.022×1023 mol−1.[26] Molar concentration
Molar concentration
is the amount of a particular substance per volume of solution, and is commonly reported in moldm−3.[27] Phase

Diagram showing relationships among the phases and the terms used to describe phase changes.

Main article: Phase 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 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. Many substances exhibit multiple solid phases. For example, there are three phases of solid iron (alpha, gamma, and delta) that vary based on temperature and pressure. A principal difference between solid phases is the crystal structure, or arrangement, of the atoms. Another phase commonly encountered in the study of chemistry is the aqueous phase, which is the state of substances dissolved in aqueous solution (that is, in water). Less familiar phases include plasmas, Bose–Einstein condensates and fermionic condensates and the paramagnetic and ferromagnetic phases of 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. Bonding Main article: Chemical bond

An animation of the process of ionic bonding between sodium (Na) and chlorine (Cl) to form sodium chloride, or common table salt. Ionic bonding involves one atom taking valence electrons from another (as opposed to sharing, which occurs in covalent bonding)

Atoms
Atoms
sticking together in molecules or crystals are said to be bonded with one another. A chemical bond 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. A chemical bond can be a covalent bond, an ionic bond, a hydrogen bond or just because of Van der Waals force. Each of these kinds of bonds is ascribed to some potential. These potentials create the interactions which hold atoms together 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 explain molecular structure and composition. An ionic bond is formed when a metal loses one or more of its electrons, becoming a positively charged cation, and the electrons are then gained by the non-metal atom, becoming a negatively charged anion. The two oppositely charged ions attract one another, and the ionic bond is the electrostatic force of attraction between them. For example, sodium (Na), a metal, loses one electron to become an Na+ cation while chlorine (Cl), a non-metal, gains this electron to become Cl−. The ions are held together due to electrostatic attraction, and that compound sodium chloride (NaCl), or common table salt, is formed.

In the methane molecule (CH4), the carbon atom shares a pair of valence electrons with each of the four hydrogen atoms. Thus, the octet rule is satisfied for C-atom (it has eight electrons in its valence shell) and the duet rule is satisfied for the H-atoms (they have two electrons in their valence shells).

In a covalent bond, one or more pairs of valence electrons are shared by two atoms: the resulting electrically neutral group of bonded atoms is termed a molecule. Atoms
Atoms
will share valence electrons in such a way as to create a noble gas electron configuration (eight electrons in their outermost shell) for each atom. Atoms
Atoms
that tend to combine in such a way that they each have eight electrons in their valence shell are said to follow the octet rule. However, some elements like hydrogen and lithium need only two electrons in their outermost shell to attain this stable configuration; these atoms are said to follow the duet rule, and in this way they are reaching the electron configuration of the noble gas helium, which has two electrons in its outer shell. Similarly, theories from classical physics can be used to predict many ionic structures. With more complicated compounds, such as metal complexes, valence bond theory is less applicable and alternative approaches, such as the molecular orbital theory, are generally used. See diagram on electronic orbitals. Energy Main article: Energy In the context of chemistry, energy is an attribute of a substance as a consequence of its atomic, molecular or aggregate structure. Since a chemical transformation is accompanied by a change in one or more of these kinds of structures, it 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 exergonic if the final state is lower on the energy scale than the initial state; in the case of endergonic reactions the situation is the reverse. A reaction is said to be exothermic if the reaction releases heat to the surroundings; in the case of endothermic reactions, the reaction absorbs heat from the surroundings. 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

e

− E

/

k T

displaystyle e^ -E/kT

– that is the probability of a 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 to occur can be in the form of heat, light, electricity or mechanical force in the form of ultrasound.[29] A related concept free energy, which also incorporates entropy considerations, 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
Gibbs free energy
is negative,

Δ G ≤ 0

displaystyle Delta Gleq 0,

; if it is equal to zero the chemical reaction is said to be at equilibrium. There exist only 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 a 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, more amenable to chemical reactions. The phase of a substance is invariably determined by its energy and the energy of its surroundings. When the intermolecular forces of a substance are such that the 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.[30] 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 another depends on the size of energy quanta emitted from one substance. However, heat energy is often transferred more easily from almost any substance to another because the phonons responsible for vibrational and rotational energy levels in a substance have much less energy than photons invoked for the electronic energy transfer. Thus, because vibrational and rotational energy levels are more closely spaced than electronic energy levels, heat is more easily transferred between substances relative to light or other forms of electronic energy. For example, ultraviolet electromagnetic radiation is not transferred with as much efficacy from one substance to another as thermal or electrical energy. The existence of characteristic energy levels for different chemical substances is useful for their identification by the analysis of spectral lines. Different kinds of spectra are often used in chemical spectroscopy, e.g. IR, microwave, NMR, ESR, etc. Spectroscopy
Spectroscopy
is also used to identify the composition of remote objects – like stars and distant galaxies – by analyzing their radiation spectra.

Emission spectrum of iron

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

During chemical reactions, bonds between atoms break and form, resulting in different substances with different properties. In a blast furnace, iron oxide, a compound, reacts with carbon monoxide to form iron, one of the chemical elements, and carbon dioxide.

When a chemical substance is transformed as a result of its interaction with another substance or with energy, a chemical reaction is said to have occurred. A chemical reaction is therefore a concept related to the "reaction" of a substance when it comes in close contact with another, whether as a mixture or a solution; exposure to some form of energy, or both. It results in some energy exchange between the constituents of the reaction as well as with the system environment, which may be designed vessels—often laboratory glassware. Chemical reactions can result in the formation or dissociation of molecules, that is, 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. Oxidation, reduction, dissociation, acid-base neutralization and molecular 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.[31] 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 mechanism. A chemical reaction can be envisioned to take place in a number of steps, each of which may have a different speed. Many reaction intermediates with variable stability can thus be envisaged during the course of a reaction. Reaction mechanisms are proposed to explain the kinetics and the relative product mix of a reaction. Many physical chemists specialize in exploring and proposing the mechanisms of various chemical reactions. Several empirical rules, like the Woodward–Hoffmann rules
Woodward–Hoffmann rules
often come in handy while proposing a mechanism for a chemical reaction. According to the IUPAC
IUPAC
gold book, a chemical reaction is "a process that results in the interconversion of chemical species."[32] Accordingly, 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'). Ions and salts

The crystal lattice structure of potassium chloride (KCl), a salt which is formed due to the attraction of K+ cations and Cl− anions. Note how the overall charge of the ionic compound is zero.

Main article: Ion An ion is a charged species, an atom or a molecule, that has lost or gained one or more electrons. When an atom loses an electron and thus has more protons than electrons, the atom is a positively charged ion or cation. When an atom gains an electron and thus has more electrons than protons, the atom is a negatively charged ion or anion. Cations and anions can form a crystalline lattice of neutral salts, such as the Na+ and Cl− ions forming sodium chloride, or NaCl. Examples of polyatomic ions that do not split up during acid-base reactions are hydroxide (OH−) and phosphate (PO43−). Plasma is composed of gaseous matter that has been completely ionized, usually through high temperature. Acidity and basicity

When hydrogen bromide (HBr), pictured, is dissolved in water, it forms the strong acid hydrobromic acid

Main article: Acid–base reaction A substance can often be classified as an acid or a base. There are several different theories which explain acid-base behavior. The simplest is Arrhenius theory, which states than an acid is a substance that produces hydronium ions when it is dissolved in water, and a base is one that produces hydroxide ions when dissolved in water. According to Brønsted–Lowry acid–base theory, acids are substances that donate a positive hydrogen ion to another substance in a chemical reaction; by extension, a base is the substance which receives that hydrogen ion. A third common theory is Lewis acid-base theory, which is based on the formation of new chemical bonds. Lewis theory explains that an acid is a substance which is capable of accepting a pair of electrons from another substance during the process of bond formation, while a base is a substance which can provide a pair of electrons to form a new bond. According to this theory, the crucial things being exchanged are charges.[33] There are several other ways in which a substance may be classified as an acid or a base, as is evident in the history of this concept.[34] Acid strength is commonly measured by two methods. One measurement, based on the Arrhenius definition of acidity, is pH, which is a measurement of the hydronium ion concentration in a solution, as expressed on a negative logarithmic scale. Thus, solutions that have a low pH have a high hydronium ion concentration, and can be said to be more acidic. The other measurement, based on the Brønsted–Lowry definition, is the acid dissociation constant (Ka), which measures the relative ability of a substance to act as an acid under the Brønsted–Lowry definition of an acid. That is, substances with a higher Ka are more likely to donate hydrogen ions in chemical reactions than those with lower Ka values. Redox Main article: Redox Redox
Redox
(reduction-oxidation) reactions include all chemical reactions in which atoms have their oxidation state changed by either gaining electrons (reduction) or losing electrons (oxidation). Substances that have the ability to oxidize other substances are said to be oxidative and are known as oxidizing agents, oxidants or oxidizers. An oxidant removes electrons from another substance. Similarly, substances that have the ability to reduce other substances are said to be reductive and are known as reducing agents, reductants, or reducers. A reductant transfers electrons to another substance, and is thus oxidized itself. And because it "donates" electrons it is also called an electron donor. Oxidation and reduction properly refer to a change in oxidation number—the actual transfer of electrons may never occur. Thus, oxidation is better defined as an increase in oxidation number, and reduction as a decrease in oxidation number. Equilibrium Main article: Chemical equilibrium Although the concept of equilibrium is widely used across sciences, in the context of chemistry, it arises whenever a number of different states of the chemical composition are possible, as for example, in a mixture of several chemical compounds that can react with one another, or when a substance can be present in more than one kind of phase. A system of chemical substances at equilibrium, even though having an unchanging composition, is most often not static; molecules of the substances continue to react with one another thus giving rise to a dynamic equilibrium. Thus the concept describes the state in which the parameters such as chemical composition remain unchanged over time. Chemical laws Main article: Chemical law Chemical reactions are governed by certain laws, which have become fundamental concepts in chemistry. Some of them are:

Avogadro's law Beer–Lambert law Boyle's law
Boyle's law
(1662, relating pressure and volume) Charles's law
Charles's law
(1787, relating volume and temperature) Fick's laws of diffusion Gay-Lussac's law (1809, relating pressure and temperature) Le Chatelier's principle Henry's law Hess's law Law of conservation of energy leads to the important concepts of equilibrium, thermodynamics, and kinetics. Law of conservation of mass
Law of conservation of mass
continues to be conserved in isolated systems, even in modern physics. However, special relativity shows that due to mass–energy equivalence, whenever non-material "energy" (heat, light, kinetic energy) is removed from a non-isolated system, some mass will be lost with it. High energy losses result in loss of weighable amounts of mass, an important topic in nuclear chemistry. 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 Raoult's law

History Of definition The definition of chemistry has changed over time, as new discoveries and theories add to the functionality of the science. The term "chymistry", in the view of noted scientist Robert Boyle
Robert Boyle
in 1661, meant the subject of the material principles of mixed bodies.[35] In 1663 the chemist Christopher Glaser described "chymistry" as 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 a higher perfection.[36] The 1730 definition of the word "chemistry", as used by Georg Ernst Stahl, meant the art of resolving mixed, compound, or aggregate bodies into their principles; and of composing such bodies from those principles.[37] In 1837, Jean-Baptiste Dumas
Jean-Baptiste Dumas
considered the word "chemistry" to refer to the science concerned with the laws and effects of molecular forces.[38] This definition further evolved until, in 1947, it came to mean the science of substances: their structure, their properties, and the reactions that change them into other substances - a characterization accepted by Linus Pauling.[39] More recently, in 1998, Professor Raymond Chang broadened the definition of "chemistry" to mean the study of matter and the changes it undergoes.[40] Of discipline Main article: History of chemistry See also: Alchemy
Alchemy
and Timeline of chemistry

Democritus' atomist philosophy was later adopted by Epicurus (341–270 BCE).

Early civilizations, such as the Egyptians[41] Babylonians, Indians[42] amassed practical knowledge concerning the arts of metallurgy, pottery and dyes, but didn't develop a systematic theory. A basic chemical hypothesis first emerged in Classical Greece
Classical Greece
with the theory of four elements as propounded definitively by Aristotle stating that fire, air, earth and water were the fundamental elements from which everything is formed as a combination. Greek atomism dates back to 440 BC, arising in works by philosophers such as Democritus and Epicurus. In 50 BC, the Roman philosopher Lucretius
Lucretius
expanded upon the theory in his book De rerum natura
De rerum natura
(On The Nature of Things).[43][44] Unlike modern concepts of science, Greek atomism was purely philosophical in nature, with little concern for empirical observations and no concern for chemical experiments.[45] In the Hellenistic world
Hellenistic world
the art of alchemy first proliferated, mingling magic and occultism into the study of natural substances with the ultimate goal of transmuting elements into gold and discovering the elixir of eternal life.[46] Work, particularly the development of distillation, continued in the early Byzantine
Byzantine
period with the most famous practitioner being the 4th century Greek-Egyptian Zosimos of Panopolis.[47] Alchemy
Alchemy
continued to be developed and practised throughout the Arab world
Arab world
after the Muslim conquests,[48] and from there, and from the Byzantine
Byzantine
remnants,[49] diffused into medieval and Renaissance
Renaissance
Europe through Latin translations. Some influential Muslim chemists, Abū al-Rayhān al-Bīrūnī,[50] Avicenna[51] and Al-Kindi refuted the theories of alchemy, particularly the theory of the transmutation of metals; and al-Tusi described a version of the conservation of mass, noting that a body of matter is able to change but is not able to disappear.[52]

Jābir ibn Hayyān
Jābir ibn Hayyān
(Geber), a Perso-Arab alchemist whose experimental research laid the foundations of chemistry.

The development of the modern scientific method was slow and arduous, but an early scientific method for chemistry began emerging among early Muslim chemists, beginning with the 9th century Perso-Arab chemist Jābir ibn Hayyān
Jābir ibn Hayyān
(known as "Geber" in Europe), who is sometimes referred to as "the father of chemistry".[53][54][55][56] He introduced a systematic and experimental approach to scientific research based in the laboratory, in contrast to the ancient Greek and Egyptian alchemists whose works were largely allegorical and often unintelligble.[57] Under the influence of the new empirical methods propounded by Sir Francis Bacon
Sir Francis Bacon
and others, a group of chemists at Oxford, Robert Boyle, Robert Hooke
Robert Hooke
and John Mayow
John Mayow
began to reshape the old alchemical traditions into a scientific discipline. Boyle in particular is regarded as the founding father of chemistry due to his most important work, the classic chemistry text The Sceptical Chymist where the differentiation is made between the claims of alchemy and the empirical scientific discoveries of the new chemistry.[58] He formulated Boyle's law, rejected the classical "four elements" and proposed a mechanistic alternative of atoms and chemical reactions that could be subject to rigorous experiment.[59]

Antoine-Laurent de Lavoisier
Antoine-Laurent de Lavoisier
is considered the "Father of Modern Chemistry".[60]

The theory of phlogiston (a substance at the root of all combustion) was propounded by the German Georg Ernst Stahl
Georg Ernst Stahl
in the early 18th century and was only overturned by the end of the century by the French chemist Antoine Lavoisier, the chemical analogue of Newton in physics; who did more than any other to establish the new science on proper theoretical footing, by elucidating the principle of conservation of mass and developing a new system of chemical nomenclature used to this day.[61] Before his work, though, many important discoveries had been made, specifically relating to the nature of 'air' which was discovered to be composed of many different gases. The Scottish chemist Joseph Black (the first experimental chemist) and the Dutchman J. B. van Helmont discovered carbon dioxide, or what Black called 'fixed air' in 1754; Henry Cavendish
Henry Cavendish
discovered hydrogen and elucidated its properties and Joseph Priestley
Joseph Priestley
and, independently, Carl Wilhelm Scheele
Carl Wilhelm Scheele
isolated pure oxygen.

In his periodic table, Dmitri Mendeleev
Dmitri Mendeleev
predicted the existence of 7 new elements,[62] and placed all 60 elements known at the time in their correct places.[63]

English scientist John Dalton
John Dalton
proposed the modern theory of atoms; that all substances are composed of indivisible 'atoms' of matter and that different atoms have varying atomic weights. The development of the electrochemical theory of chemical combinations occurred in the early 19th century as the result of the work of two scientists in particular, J. J. Berzelius
J. J. Berzelius
and Humphry Davy, made possible by the prior invention of the voltaic pile by Alessandro Volta. Davy discovered nine new elements including the alkali metals by extracting them from their oxides with electric current.[64] British William Prout
William Prout
first proposed ordering all the elements by their atomic weight as all atoms had a weight that was an exact multiple of the atomic weight of hydrogen. J. A. R. Newlands
J. A. R. Newlands
devised an early table of elements, which was then developed into the modern periodic table of elements[65] in the 1860s by Dmitri Mendeleev
Dmitri Mendeleev
and independently by several other scientists including Julius Lothar Meyer.[66][67] The inert gases, later called the noble gases were discovered by William Ramsay
William Ramsay
in collaboration with Lord Rayleigh
Lord Rayleigh
at the end of the century, thereby filling in the basic structure of the table.

Top: Expected results: alpha particles passing through the plum pudding model of the atom undisturbed. Bottom: Observed results: a small portion of the particles were deflected, indicating a small, concentrated charge.

At the turn of the twentieth century the theoretical underpinnings of chemistry were finally understood due to a series of remarkable discoveries that succeeded in probing and discovering the very nature of the internal structure of atoms. In 1897, J. J. Thomson
J. J. Thomson
of Cambridge University
Cambridge University
discovered the electron and soon after the French scientist Becquerel
Becquerel
as well as the couple Pierre and Marie Curie investigated the phenomenon of radioactivity. In a series of pioneering scattering experiments Ernest Rutherford
Ernest Rutherford
at the University of Manchester discovered the internal structure of the atom and the existence of the proton, classified and explained the different types of radioactivity and successfully transmuted the first element by bombarding nitrogen with alpha particles. His work on atomic structure was improved on by his students, the Danish physicist Niels Bohr
Niels Bohr
and Henry Moseley. The electronic theory of chemical bonds and molecular orbitals was developed by the American scientists Linus Pauling
Linus Pauling
and Gilbert N. Lewis. The year 2011 was declared by the United Nations as the International Year of Chemistry.[68] It was an initiative of the International Union of Pure and Applied Chemistry, and of the United Nations Educational, Scientific, and Cultural Organization and involves chemical societies, academics, and institutions worldwide and relied on individual initiatives to organize local and regional activities. Organic chemistry
Organic chemistry
was developed by Justus von Liebig
Justus von Liebig
and others, following Friedrich Wöhler's synthesis of urea which proved that living organisms were, in theory, reducible to chemistry.[69] Other crucial 19th century advances were; an understanding of valence bonding ( Edward Frankland
Edward Frankland
in 1852) and the application of thermodynamics to chemistry ( J. W. Gibbs
J. W. Gibbs
and Svante Arrhenius
Svante Arrhenius
in the 1870s). Practice Subdisciplines

This article relies largely or entirely on a single source. Relevant discussion may be found on the talk page. Please help improve this article by introducing citations to additional sources. (September 2014)

Chemistry
Chemistry
is typically divided into several major sub-disciplines. There are also several main cross-disciplinary and more specialized fields of chemistry.[70]

Analytical 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 subdisciplines of chemistry, excluding purely theoretical chemistry. Biochemistry
Biochemistry
is the study of the chemicals, chemical reactions and chemical interactions that take place in living organisms. Biochemistry
Biochemistry
and organic chemistry are closely related, as in medicinal chemistry or neurochemistry. Biochemistry
Biochemistry
is also associated with molecular biology and genetics. 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. 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. Neurochemistry
Neurochemistry
is the study of neurochemicals; including transmitters, peptides, proteins, lipids, sugars, and nucleic acids; their interactions, and the roles they play in forming, maintaining, and modifying the nervous system. 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
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
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, spectroscopy, and more recently, astrochemistry.[71] Physical chemistry has large overlap with molecular physics. Physical chemistry involves the use of infinitesimal calculus in deriving equations. It is usually associated with quantum chemistry and theoretical chemistry. Physical chemistry
Physical chemistry
is a distinct discipline from chemical physics, but again, there is very strong overlap. 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 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 (carbon-based) matter; biochemistry, the study of substances found in biological organisms; physical chemistry, the study of chemical processes using physical concepts such as thermodynamics and quantum mechanics; and 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 nervous system (see subdisciplines). Other fields include agrochemistry, astrochemistry (and cosmochemistry), atmospheric chemistry, chemical engineering, chemical biology, chemo-informatics, electrochemistry, environmental chemistry, femtochemistry, flavor chemistry, flow chemistry, geochemistry, green chemistry, histochemistry, history of chemistry, hydrogenation chemistry, immunochemistry, marine chemistry, materials science, mathematical chemistry, mechanochemistry, medicinal chemistry, molecular biology, molecular mechanics, nanotechnology, natural product chemistry, oenology, organometallic chemistry, petrochemistry, pharmacology, photochemistry, physical organic chemistry, phytochemistry, polymer chemistry, radiochemistry, solid-state chemistry, sonochemistry, supramolecular chemistry, surface chemistry, synthetic chemistry, thermochemistry, and many others. Industry Main article: Chemical industry The chemical industry represents an important economic activity worldwide. The global top 50 chemical producers in 2013 had sales of US$980.5 billion with a profit margin of 10.3%.[72] Professional societies

American Chemical Society American Society for Neurochemistry Chemical Institute of Canada Chemical Society of Peru International Union of Pure and Applied Chemistry Royal Australian Chemical Institute Royal Netherlands Chemical Society Royal Society of Chemistry Society of Chemical Industry World Association of Theoretical and Computational Chemists List of chemistry societies

See also

Book: Chemistry

Chemistry
Chemistry
portal Science portal

Outline of chemistry Glossary of chemistry terms Common chemicals International Year of Chemistry List of chemists List of compounds List of important publications in chemistry Comparison of software for molecular mechanics modeling List of unsolved problems in chemistry Periodic systems of small molecules Philosophy of chemistry

References

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Lab. Retrieved 2011-06-12.  ^ Strathern, P. (2000). Mendeleyev's Dream – the Quest for the Elements. New York: Berkley Books. ^ a b "alchemy", entry in The Oxford
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Chemistry
IUPAC
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Recommendations 2005. RSCPublishing. pp. 5–12. ISBN 0-85404-438-8.  ^ Hill, J.W.; Petrucci, R.H.; McCreary, T.W.; Perry, S.S. (2005). General Chemistry
Chemistry
(4th ed.). Upper Saddle River, New Jersey: Pearson Prentice Hall. p. 37.  ^ M. M. Avedesian; Hugh Baker. Magnesium and Magnesium Alloys. ASM International. p. 59.  ^ "Official SI Unit definitions". Bipm.org. Retrieved 2011-06-12.  ^ Burrows et al. 2008, p. 16. ^ Atkins & de Paula 2009, p. 9. ^ Visionlearning. "Chemical Bonding by Anthony Carpi, Ph". visionlearning. Retrieved 2011-06-12.  ^ Reilly, Michael. (2007). Mechanical force induces chemical reaction, NewScientist.com news service, Reilly ^ Changing States of Matter
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Lucretius
(50 BCE). "de Rerum Natura (On the Nature of Things)". The Internet Classics Archive. Massachusetts Institute of Technology. Retrieved 9 January 2007.  Check date values in: date= (help) ^ Simpson, David (29 June 2005). " Lucretius
Lucretius
(c. 99 – c. 55 BCE)". The Internet History of Philosophy. Retrieved 2007-01-09.  ^ Strodach, George K. (2012). The Art of Happiness. New York: Penguin Classics. pp. 7–8. ISBN 0-14-310721-6.  ^ " International Year of Chemistry
International Year of Chemistry
– The History of Chemistry". G.I.T. Laboratory
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Mathematics
for the nonmathematician. Courier Dover Publications. p. 284. ISBN 0-486-24823-2 ^ Marcelin Berthelot, Collection des anciens alchimistes grecs (3 vol., Paris, 1887–1888, p. 161); F. Sherwood Taylor, "The Origins of Greek Alchemy," Ambix 1 (1937), 40. ^ Marmura, Michael E.; Nasr, Seyyed Hossein (1965). "An Introduction to Islamic Cosmological Doctrines. Conceptions of Nature and Methods Used for Its Study by the Ikhwan Al-Safa'an, Al-Biruni, and Ibn Sina by Seyyed Hossein Nasr". Speculum. 40 (4): 744–746. doi:10.2307/2851429. JSTOR 2851429.  ^ Robert Briffault (1938). The Making of Humanity, pp. 196–197. ^ Alakbarov, Farid (2001). "A 13th-Century Darwin? Tusi's Views on Evolution". Azerbaijan International. 9: 2.  ^ Derewenda, Zygmunt S.; Derewenda, ZS (2007). "On wine, chirality and crystallography". Acta Crystallographica Section A. 64 (Pt 1): 246–258 [247]. Bibcode:2008AcCrA..64..246D. doi:10.1107/S0108767307054293. PMID 18156689.  ^ John Warren (2005). "War and the Cultural Heritage of Iraq: a sadly mismanaged affair", Third World Quarterly, Volume
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26, Issue 4 & 5, pp. 815–830. ^ Dr. A. Zahoor (1997), Jâbir ibn Hayyân (Geber) ^ Paul Vallely, How Islamic inventors changed the world, The Independent, 10 March 2006 ^ Kraus, Paul, Jâbir ibn Hayyân, Contribution à l'histoire des idées scientifiques dans l'Islam. I. Le corpus des écrits jâbiriens. II. Jâbir et la science grecque,. Cairo (1942–1943). Repr. By Fuat Sezgin, (Natural Sciences in Islam. 67–68), Frankfurt. 2002:

"To form an idea of the historical place of Jabir's alchemy and to tackle the problem of its sources, it is advisable to compare it with what remains to us of the alchemical literature in the Greek language. One knows in which miserable state this literature reached us. Collected by Byzantine
Byzantine
scientists from the tenth century, the corpus of the Greek alchemists is a cluster of incoherent fragments, going back to all the times since the third century until the end of the Middle Ages."

"The efforts of Berthelot and Ruelle to put a little order in this mass of literature led only to poor results, and the later researchers, among them in particular Mrs. Hammer-Jensen, Tannery, Lagercrantz, von Lippmann, Reitzenstein, Ruska, Bidez, Festugiere and others, could make clear only few points of detail…

The study of the Greek alchemists is not very encouraging. An even surface examination of the Greek texts shows that a very small part only was organized according to true experiments of laboratory: even the supposedly technical writings, in the state where we find them today, are unintelligible nonsense which refuses any interpretation.

It is different with Jabir's alchemy. The relatively clear description of the processes and the alchemical apparatuses, the methodical classification of the substances, mark an experimental spirit which is extremely far away from the weird and odd esotericism of the Greek texts. The theory on which Jabir supports his operations is one of clearness and of an impressive unity. More than with the other Arab authors, one notes with him a balance between theoretical teaching and practical teaching, between the `ilm and the `amal. In vain one would seek in the Greek texts a work as systematic as that which is presented for example in the Book
Book
of Seventy."

(cf. Ahmad Y Hassan. "A Critical Reassessment of the Geber Problem: Part Three". Archived from the original on 2008-11-20. Retrieved 2008-08-09. )

^ "Robert Boyle, Founder of Modern Chemistry" Harry Sootin (2011) ^ "History – Robert Boyle
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Julius Lothar Meyer
and Dmitri Ivanovich Mendeleev". Science History Institute. Retrieved March 20, 2018.  ^ "What makes these family likenesses among the elements? In the 1860s everyone was scratching their heads about that, and several scientists moved towards rather similar answers. The man who solved the problem most triumphantly was a young Russian called Dmitri Ivanovich Mendeleev, who visited the salt mine at Wieliczka in 1859." Bronowski, Jacob (1973). The Ascent of Man. Little, Brown and Company. p. 322. ISBN 0-316-10930-4.  ^ "Chemistry". Chemistry2011.org. Retrieved 2012-03-10.  ^ Ihde, Aaron John (1984). The Development of Modern Chemistry. Courier Dover Publications. p. 164. ISBN 0-486-64235-6.  ^ W.G. Laidlaw; D.E. Ryan And Gary Horlick; H.C. Clark, Josef Takats, And Martin Cowie; R.U. Lemieux (1986-12-10). "Chemistry Subdisciplines". The Canadian Encyclopedia. Retrieved 2011-06-12. CS1 maint: Multiple names: authors list (link) ^ Herbst, Eric (May 12, 2005). " Chemistry
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Bibliography

Atkins, Peter; de Paula, Julio (2009) [1992]. Elements of Physical Chemistry
Chemistry
(5th ed.). New York: Oxford
Oxford
University Press. ISBN 978-0-19-922672-6.  Burrows, Andrew; Holman, John; Parsons, Andrew; Pilling, Gwen; Price, Gareth (2009). Chemistry3. Italy: Oxford
Oxford
University Press. ISBN 978-0-19-927789-6.  Housecroft, Catherine E.; Sharpe, Alan G. (2008) [2001]. Inorganic Chemistry
Chemistry
(3rd ed.). Harlow, Essex: Pearson Education. ISBN 978-0-13-175553-6. 

Further reading

Popular reading

Atkins, P.W. Galileo's Finger ( Oxford
Oxford
University Press) ISBN 0-19-860941-8 Atkins, P.W. Atkins' Molecules
Molecules
( Cambridge University
Cambridge University
Press) ISBN 0-521-82397-8 Kean, Sam. The Disappearing Spoon - and other true tales from the Periodic Table (Black Swan) London, 2010 ISBN 978-0-552-77750-6 Levi, Primo The Periodic Table (Penguin Books) [1975] translated from the Italian by Raymond Rosenthal (1984) ISBN 978-0-14-139944-7 Stwertka, A. A Guide to the Elements ( Oxford
Oxford
University Press) ISBN 0-19-515027-9 "Dictionary of the History of Ideas". Archived from the original on March 10, 2008.   "Chemistry". Encyclopædia Britannica. 6 (11th ed.). 1911. pp. 33–76. 

Introductory undergraduate text books

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 Chang, Raymond. Chemistry
Chemistry
6th ed. Boston: James M. Smith, 1998. ISBN 0-07-115221-0. Clayden, Jonathan; Greeves, Nick; Warren, Stuart; Wothers, Peter (2001). Organic Chemistry
Chemistry
(1st ed.). Oxford
Oxford
University Press. ISBN 978-0-19-850346-0.  Voet and Voet Biochemistry
Biochemistry
(Wiley) ISBN 0-471-58651-X

Advanced undergraduate-level or graduate text books

Atkins, P.W. Physical Chemistry
Chemistry
( Oxford
Oxford
University Press) ISBN 0-19-879285-9 Atkins, P.W. et al. Molecular Quantum Mechanics ( Oxford
Oxford
University Press) McWeeny, R. Coulson's Valence ( Oxford
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
Chemistry
(Dover Publications) ISBN 0-486-64871-0 Smart and Moore Solid
Solid
State Chemistry: An Introduction (Chapman and Hall) ISBN 0-412-40040-5 Stephenson, G. Mathematical Methods for Science Students (Longman) ISBN 0-582-44416-0

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