Glossary of chemistry

This glossary of chemistry terms is a list of terms and definitions relevant to chemistry, including chemical laws, diagrams and formulae, laboratory tools, glassware, and equipment. Chemistry is a physical science concerned with the composition, structure, and properties of matter, as well as the changes it undergoes during chemical reactions; it features an extensive vocabulary and a significant amount of jargon.

Note: All periodic table references refer to the IUPAC Style of the Periodic Table.

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• Avogadro's number Also Avogadro constant. The number of discrete constituent particles (such as molecules, atoms, or ions) in one mole of a substance, defined as exactly 6.02214076Template:E such particles.
• Boyle's law For a given mass of gas at constant temperature, the volume varies inversely with the pressure.  
• Brønsted–Lowry acid Any chemical species that readily donates a proton.  
• Brønsted–Lowry base Any chemical species that readily accepts a proton.  
• Charles's law When the pressure on a sample of a dry gas is held constant, the Kelvin temperature is directly proportional to its volume.  
• Commission on Isotopic Abundances and Atomic Weights (CIAAW)  
• Dewar flask See vacuum flask.  
• Eppendorf tube A generalized and trademarked name used to refer to a microcentrifuge tube.  
• Erlenmeyer flask [[]]   A 500-milliliter Erlenmeyer flask  
• Faraday constant A unit of electric charge widely used in electrochemistry which represents 1 mole of electrons: 6.022 × 1023 electrons. It is equal to approximately 96,500 coulombs (F = 96 485.339 9(24) C/mol).  
• Faraday's laws of electrolysis A set of two laws pertaining to electrolysis which hold that: a) the mass of a substance altered at an electrode during electrolysis is directly proportional to the quantity of electricity transferred at that electrode; and b) the mass of an elemental material altered at an electrode is directly proportional to the element's equivalent weight.

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G-K

• Gay-Lussac's law A chemical law used for each of the two relationships derived by French chemist Joseph Louis Gay-Lussac and which concern the properties of gases, though the name is more usually applied to his law of combining volumes.  
• Gibbs energy A value that indicates the spontaneity of a reaction. Usually symbolized as G.  
• Hess' law of constant heat summation Also simply called Hess' law. A law of physical chemistry which states that the total enthalpy change during the course of a chemical reaction is the same whether the reaction is completed in one step or in multiple steps.  
• International Union of Pure and Applied Chemistry (IUPAC) An international federation of chemists that is recognized as the world authority in developing standards for chemical nomenclature and other methodologies in chemistry.

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L-N

• London dispersion forces A type of weak intermolecular force.  
• Raoult's law A law of thermodynamics which states that the partial pressure of each gaseous component of an ideal mixture of liquids is equal to the vapor pressure of the pure component multiplied by its molar fraction in the mixture.  
• Schrödinger equation A quantum state equation which represents the behaviour of an electron around an atom.  
• Tyndall effect The effect of light scattering by colloidal or suspended particles.  
• UN number A four-digit code used to note hazardous and flammable substances.  
• X-ray diffraction a method for establishing structures of crystalline solids using single wavelength X-rays and looking at diffraction pattern.  
• X-ray photoelectron spectroscopy A spectroscopic technique used to measure the composition of a material.
• X-ray A form of ionizing, electromagnetic radiation between gamma and UV rays in the electromagnetic spectrum.  
• absolute zero A theoretical condition concerning a system at the lowest limit of the thermodynamic temperature scale, or zero kelvins, at which the system does not emit or absorb energy (i.e. all atoms are at rest). By extrapolating the ideal gas law, the internationally agreed-upon value for absolute zero has been determined as −273.15 °C (−459.67 °F; 0.00 K).  
• absorption 1.  The physical or chemical process by which a substance in one state becomes incorporated into and retained by another substance of a different state. Absorption differs from adsorption in that the first substance permeates the entire bulk of the second substance, rather than just adhering to the surface.2.  The process by which matter (typically electrons bound in atoms) takes up the energy of electromagnetic radiation and transforms it into any of various types of internal energy, such as thermal energy. This type of absorption is the principle on which spectrophotometry is based.

More terms

• accuracy How close a measured value is to the actual or true value. Compare precision.  
• acid anhydride A compound with two acyl groups bound to a single oxygen atom.  
• acid dissociation constant (Ka) Also acid ionization constant or acidity constant. A quantitative measure of the strength of an acid in solution expressed as an equilibrium constant for a chemical dissociation reaction in the context of acid-base reactions. It is often given as its base-10 cologarithm, pKa.  
• acid A compound which, when dissolved in water, gives a pH of less than 7.0, or donates a hydrogen ion.  
• actinides Also actinoids. The periodic series of metallic elements with atomic numbers 89 to 103, from actinium through lawrencium.  
• activated complex A structure that forms because of a collision between molecules while new bonds are formed.  
• activation energy The minimum energy which must be available to a chemical system with potential reactants in order to result in a chemical reaction.  
• activity series See reactivity series.
• acyclic Containing only linear structures of atoms (particularly in hydrocarbons).  
• addition reaction In organic chemistry, when two or more molecules combine to make a larger one.   The tendency of dissimilar particles or surfaces to cling to one another as a result of intermolecular forces. Contrast cohesion.  
• adsorption The chemical adhesion of atoms, ions, or molecules of one substance (either a gas, liquid, or dissolved solid) to the surface of another substance, resulting in a film of the first substance being weakly bonded to the interface between the two substances. Adsorption differs from absorption in that it is exclusively a surface phenomenon, while absorption involves entire volumes of materials.  
• aeration The mixing of air into a liquid or a solid.  
• alcohol Any organic compound consisting of a hydroxyl functional group attached to a saturated carbon atom.  
• aldehyde Any organic compound consisting of a carbonyl group attached to a hydrogen atom and any other R-group.  
• alkali metal Any of the metallic elements belonging to Group 1 of the periodic table: lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs), and francium (Fr).  
• alkaline earth metal Any of the metallic elements belonging to Group 2 of the periodic table: beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra).  
• alkane Any saturated acyclic hydrocarbon.  
• alkene An unsaturated hydrocarbon containing at least one pair of double-bonded carbons.  
• alkyl group A functional group consisting of an alkane missing a hydrogen atom.  
• alkyne An unsaturated hydrocarbon containing at least one pair of triple-bonded carbons.  
• allomer A substance that differs in chemical composition but has the same crystalline structure as another substance.  
• allotrope Elements that can have different structures (and therefore different forms), such as carbon (diamonds, graphite, and fullerene).  
• alloy A mixture of metals or of a metal and another element which in combination exhibit a metallic bonding character. Common examples include bronze, brass, and pewter.  
• amalgam Any alloy of mercury with another metal.  
• amount of substance Also enplethy, chemical amount, or simply amount. The number of discrete particles (such as molecules, atoms, ions, electrons, or any other atomic-scale entity) in a given sample of matter, divided by the Avogadro constant. The SI base unit for amount of substance is the mole (mol).  
• analytical chemistry The branch of chemistry which studies and makes use of instruments and methods to separate, quantify, and identify chemical substances, both by classical wet chemistry techniques such as precipitation, extraction, distillation, and observational analysis, and by modern instrumental techniques such as chromatography, spectroscopy, and electrochemistry.  
• anion A negatively charged ion. I.e. an atom that has an excess of electrons compared to protons.  
• anode 1.  An electrode through which the conventional electric current (the flow of positive charges) enters into a polarized electrical circuit.2.  The wire or plate of an electrochemical cell having an excess positive charge. Negatively charged anions always move toward the anode. Contrast cathode.  
• aqueous solution A solution in which the solvent is water. It is denoted in chemical equations by appending (aq) to a chemical formula.  
• aromaticity A chemical property of conjugated rings of atoms, such as benzene, which results in unusually high stability. Such rings are said to be aromatic.  
• aryl Any functional group or substituent derived from an aromatic ring, such as phenyl or naphthyl. The symbol Ar is often used as a placeholder for a generic aryl group in structural diagrams.  
• atom A chemical element in its smallest form, made up of protons and neutrons within the nucleus and electrons circling the nucleus. [[]]   An atom with protons, neutrons, and electrons labelled  
• atomic mass unit See unified atomic mass unit.  
• atomic mass The mass of an atom, typically expressed in unified atomic mass units and nearly equivalent to the mass number.  
• atomic number (Z) Also proton number. The number of protons found in the nucleus of an atom of a given chemical element. It is identical to the charge number of the nucleus and is used in the periodic table to uniquely identify each chemical element.  
• atomic orbital Any region in which one or more electrons may be found in an individual atom (as opposed to that within a molecule).  
• azeotrope A mixture of liquids whose composition is unchanged by distillation.
• barometer A device used to measure atmospheric pressure.  
• base anhydride Oxides of group I and II metal elements.  
• base A substance that accepts a proton and has a pH above 7.0. A common example is sodium hydroxide (NaOH).  
• beaker A cylindrical vessel or container with a flat bottom, most commonly a type of glassware, widely used in laboratories for a variety of purposes, such as preparing, holding, containing, collecting, or volumetrically measuring chemicals, samples, or solutions, or as a chamber in which a chemical reaction occurs. Beakers are distinguished from flasks by having straight rather than sloping sides; most beakers also have a small spout in the rim to aid pouring.  
• biochemistry The study of the chemistry of biological systems and organisms.  
• boiling point Also vaporization point. The temperature at which a substance changes state from a liquid to a gas (or vapor). It depends on pressure and is usually specified for a given substance under standard conditions.  
• boiling-point elevation the process where the boiling point is elevated by adding a substance  
• boiling See vaporization.  
• bond Any persistent attraction between atoms, ions, or molecules that enables the formation of chemical compounds. Bonds are created as a result of a wide variety of electrochemical forces, whose strengths can vary considerably; they are broken when these forces are overcome by other forces. The types, strengths, and quantities of bonds holding together chemical substances dictate the structure and bulk properties of matter.  
• buffered solution Also simply called a buffer. An aqueous solution consisting of a weak acid and its conjugate base or a weak base and its conjugate acid that resists changes in pH when strong acids or bases are added.  
• bumping A phenomenon in which a homogeneous liquid raised to its boiling point becomes superheated and, upon nucleation, rapidly boils to the gas phase, resulting in a violent expulsion of the liquid from the container; in extreme cases, the container itself may shatter. Frequent stirring, the use of an appropriate container, and the use of boiling chips can help prevent bumping.  
• burette Also spelled buret. Glassware used to dispense specific amounts of liquid when precision is necessary (e.g. during titrations and resource-dependent reactions).  
• calorimeter A device used to measure heat.  
• catalyst Any element or compound that facilitates an increase in the speed of a chemical reaction but which is not consumed or destroyed during the reaction. It is considered both a reactant and a product of the reaction.  
• cathode An electrode from which the conventional electric current (the flow of positive charges) exits a polarized electrical circuit. Positively charged cations always move toward the cathode, though the cathode's polarity can be positive or negative depending on the type of electrical device and how it is being operated. Contrast anode.  
• cation A positively charged ion.  
• cell potential The force in a galvanic cell that pulls electrons through a reducing agent to an oxidizing agent.  
• centrifugation A laboratory technique which involves the application of centrifugal force to separate particles from a solution according to their size, shape, and density. Larger and/or denser substances migrate away from the axis of a centrifuge, while smaller and/or less dense substances migrate towards the axis.  
• centrifuge A device used to separate substances based on size, shape, and density by centrifugation, or the rotation of vessels containing the substances around a centred axis at extremely high velocities.  
• charge number A quantized value of electric charge calculated as the electric charge in coulombs divided by the elementary-charge constant, or z = q/e. Charge numbers for ions are denoted in superscript (e.g. Na+ indicates a sodium ion with a charge number of positive one). Atomic numbers are charge numbers of atomic nuclei.  
• chelation A type of bonding involving the formation of two separate coordinate covalent bonds between a polydentate ligand and a single central metal ion. The ligand is usually an organic compound called a chelant or chelating agent.  
• chemical composition The identity and relative number of the elements that make up a chemical compound, which can often be expressed with a chemical formula.  
• chemical decomposition The breakdown of a single particle or entity (such as a molecule or reactive intermediate) into two or more fragments, or a chemical reaction in which two or more products are formed from a single reactant. Contrast chemical synthesis.  
• chemical formula Any of various means of concisely displaying information about the chemical composition of a compound or molecule using letters, numbers, and/or typographical symbols. Chemical formulas, such as empirical and molecular formulas, can only indicate the identities and numerical proportions of the atoms in a compound and are therefore more limited in descriptive power than chemical names and structural formulas.  
• chemical law A law of nature relevant to chemistry, such as the law of conservation of mass.  
• chemical process 1.  Any method or means of changing one or more chemicals or chemical compounds in any way, either naturally or artificially, spontaneously or by the actions of external forces.2.  In chemical engineering, any method used on an industrial scale (especially in manufacturing) to change the composition of one or more chemicals or materials.  
• chemical reaction The change of one or more substances into one or more different substances.  
• chemical species Also simply called a chemical. A chemical substance or ensemble of substances composed of chemically identical molecular entities which can explore the same set of molecular energy levels on a characteristic or delineated time scale.
• chemical substance Also pure substance or simply substance. A form of matter that has constant chemical composition and characteristic properties and which cannot be separated into simpler components by purely physical methods (i.e. without breaking chemical bonds). It is often called a pure substance to distinguish it from a mixture.  
• chemical synthesis The artificial execution of one or more chemical reactions in order to obtain one or more products. In modern laboratory contexts, specific chemical syntheses are both reliable and reproducible.  
• chemistry The scientific discipline that studies chemical substances, compounds, and molecules composed of atoms of various chemical elements, as well as their compositions, structures, properties, behaviors, and the changes they undergo during reactions with other substances.  
• cohesion The tendency of similar particles or surfaces to cling to one another as a result of intermolecular forces. Contrast adhesion.  
• colligative property Any property of a solution that depends upon the ratio of the number of solute particles to the number of solvent particles in the solution, and not on the nature of the chemical species present.  
• colloid A mixture of evenly dispersed substances, such as many milks.  
• combustion An exothermic reaction between an oxidant and a fuel that produces large amounts of heat and often light. [[]]   An example of combustion  
• compound A substance that is made up of two or more chemically bonded elements.  
• compression An area in a longitudinal wave where the particles are closer and pushed in.  
• concentration The abundance of a constituent of a mixture divided by the total volume of the mixture. Several different definitions of concentration are widely used in chemistry, including mass concentration, volume concentration, and molar concentration.  
• condensation The phase transition of a substance from a gas to a liquid.  
• condosity A comparative measurement of the electrical conductivity of a solution defined as the molar concentration of a sodium chloride (NaCl) solution that has the same specific electrical conductance as the solution under test. It is typically expressed in units of moles per litre (or per some other unit of volume).  
• conductor Any object or material that allows the flow of an electric current in one or more directions. Contrast insulator.  
• conformation The spatial arrangement of atoms affording distinction between stereoisomers which can be interconverted by rotations about formally single bonds.  
• corrosion An irreversible interfacial chemical reaction of a material with its environment which results in consumption of the material or dissolution into the material of an external component of the environment.  
• coulomb The SI unit of electric charge (symbol: C), defined as the charge transported by a constant current of one ampere in one second.  
• covalent bond Also molecular bond. A bond that involves the sharing of electron pairs between atoms. The stable balance of attractive and repulsive forces that occurs between atoms when they share electrons is known as covalent bonding. [[]]   The diatomic hydrogen molecule, H2 (right), is formed by a covalent bond when two single hydrogen atoms share two electrons  
• critical point The end point of a phase equilibrium curve or pressure-temperature curve at which conditions are such that phase boundaries vanish and a substance's different phases, such as liquid and vapor, can coexist. The critical point is defined by the intersection of a critical temperature, Tc, and a critical pressure, pc; above this temperature and pressure, all distinction between phases disappears and the substance becomes a supercritical fluid.  
• crystal A solid whose constituent particles (such as atoms, ions, or molecules) are arranged in an orderly periodic microscopic structure, forming a lattice that extends in all directions. Such materials are often described as crystalline.  
• crystallography The branch of chemistry concerned with determining the arrangement of atoms within crystalline solids.  
• cuvette A type of glassware used in spectroscopic experiments. It is usually made of plastic, glass, or quartz and should be as clean and clear as possible.
• deionization The removal of ions, and in water's case, mineral ions such as sodium, iron, and calcium.  
• deliquescence A substance's affinity for water, often characterized as its tendency to absorb moisture from the atmosphere to form aqueous solutions. Most strongly deliquescent substances are salts, such as calcium chloride and potassium carbonate.  
• delocalized electron Any electron in a molecule, ion, or solid metal that is not associated with an individual atom or covalent bond. The term may refer to electrons involved in resonance in conjugated systems or aromatic compounds; to free electrons which facilitate electrical conductivity; or to electrons within delocalized molecular orbitals encompassing several adjacent atoms.  
• density An intensive property of a substance defined as mass per unit volume and expressed by the equation d = m/V.  
• denticity The number of donor groups in a single ligand that bind to a central atom in a coordination complex.  
• deposition The settling of particles within a solution or mixture.  
• diatomic molecule Any molecule composed of only two atoms, of the same or different elements.  
• diatomic Composed of two atoms, of the same or different elements. Contrast monatomic and polyatomic.  
• diffusion The net movement of atoms or molecules from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in chemical potential of the diffusing species and depends on the random walk of particles; hence it results in mixing or mass transport without required directed bulk motion.  
• dimer An oligomer consisting of two monomers joined by chemical bonds that may variably be strong or weak, covalent or intermolecular. A homodimer consists of two identical molecules; a heterodimer consists of two different molecules.  
• dipole moment The polarity of a polar covalent bond.  
• dipole The electric or magnetic separation of charge.  
• dispersion A system in which particles of one material are distributed within a continuous phase of another material; the two phases may be in the same or different states of matter. Dispersions of particles sufficiently large for sedimentation are called suspensions, while those of smaller particles are called colloids or solutions.  
• dissolution Also solvation. The interaction of a solvent with the molecules or ions of a solute, involving bond formation, hydrogen bonding, and van der Waals forces. [[]]   A sodium ion (Na+) forms a solvation complex with water molecules when dissolved in an aqueous solution  
• distillation The process of separating the component substances of a liquid mixture by exploiting differences in the relative volatility of the mixture's components through selective boiling and subsequent condensation. The apparatus used to distill a substance is called a still, and the re-condensed substance yielded by the process is called the distillate.  
• double bond A bond involving the covalent sharing of two pairs of electrons.  
• ductility Also malleability. A measure of a material's ability to undergo significant plastic deformation before rupturing, typically expressed as percent elongation or percent area reduction from a tensile test and popularly characterized by the material's ability to be stretched into a wire.
• earth metal See alkaline earth metal.  
• electric charge A measured property (coulombs) that determines electromagnetic interaction.  
• electrochemical cell Using a chemical reaction's current, electromotive force is made.  
• electrolyte A solution that conducts a certain amount of electric current and can be split categorically into weak and strong electrolytes.  
• electromagnetic radiation A type of wave that can go through vacuums as well as material and is classified as a self-propagating wave.  
• electromagnetism Fields with an electric charge and electrical properties that change the way that particles move and interact.  
• electron configuration The distribution of the electrons of an atom or molecule within atomic or molecular orbitals. An extensive system of notation is used to concisely and uniquely display information about the electron configuration of each atomic species. Knowledge of the specific arrangements of electrons in different atoms is useful for understanding chemical bonds and the organization of the periodic table of the elements.  
• electron pair Two electrons which occupy the same molecular orbital but have opposite spins. Electron pairs form chemical bonds or occur as lone pairs of valence electrons; it is also possible for electrons to occur individually as unpaired electrons.  
• electron shell An orbital around the nucleus of an atom which contains a fixed number of electrons (usually two or eight).  
• electron A type of subatomic particle with a net charge that is negative.  
• electronegativity A chemical property that describes the tendency of an atom to attract a shared pair of electrons (or electron density) towards itself. An atom's electronegativity is affected both by its nuclear charge (which is proportional to the number of protons in its nucleus) and the number and location of the electrons present in its atomic shells (which influences the distance of the nucleus from the valence electrons). The higher an atom or substituent's electronegativity, the more it attracts electrons towards itself. As it is usually calculated, electronegativity is not a property of an atom alone but rather of an atom within a molecule; it therefore varies with an element's chemical environment, though it is generally considered a transferable property.
• electrophile Any atom or molecule which can accept an electron pair. Most electrophiles carry a net positive charge, include an atom carrying a partial positive charge, or include a neutral atom that does not have a complete octet of electrons, and therefore they attract electron-rich regions of other species; an electrophile with vacant orbitals can accept an electron pair donated by a nucleophile, creating a chemical bond between the two species. Because they accept electrons, electrophiles are Lewis acids by definition.  
• element A species of atoms having the same number of protons in their atomic nuclei and hence the same atomic number. Chemical elements constitute all of the ordinary matter in the universe; 118 elements have been identified and are organized by their various chemical properties in the periodic table of the elements.  
• elementary reaction Any chemical reaction in which one or more chemical species react directly to form products in a single reaction step and with a single transition state, i.e. without any intermediates. Contrast stepwise reaction.
• empirical formula Gives the simplest whole-number ratio of the atoms of each element present in a compound.  
• energy A system's ability to do work.  
• enplethy See amount of substance.  
• enthalpy A measure of the total internal energy of a thermodynamic system, usually symbolized by H.  
• entropy The amount of energy not available for work in a closed thermodynamic system, usually symbolized by S.  
• enzyme A biological protein catalyst that speeds up a chemical reaction.  
• equilibrium Universally, it is the condition of a system in which all competing influences are balanced. Chemical equilibrium is the state in which the concentrations of the reactants and products have stopped changing in time.  
• extensive property A physical quantity whose value is proportional to the size of the system it describes or to the quantity of matter in the system. Examples include mass, volume, enthalpy, and entropy. Contrast intensive property.
• filtration Any physical, biological, or chemical operation that separates large particles (often solid matter) from smaller particles (often a fluid) by passing the mixture through a complex lattice structure through which only particles of a sufficiently small size can pass, called a filter. The fluid and small particles which successfully pass through the filter are called the filtrate.  
• flask A vessel or container, most commonly a type of glassware, widely used in laboratories for a variety of purposes, such as preparing, holding, containing, collecting, or volumetrically measuring chemicals, samples, or solutions, or as a chamber in which a chemical reaction occurs. Flasks come in a number of shapes and sizes but are typically characterized by a wider vessel "body" and one or more narrower tubular sections with an opening at the top.  
• formal charge (FC) {{{content}}}  
• free radical See radical.    
• freezing point Also crystallization point. The temperature at which a substance changes state from a liquid to a solid. Because freezing is the reverse of melting, the freezing point of a substance is identical to its melting point, but by convention only the melting point is referred to as a characteristic property of a substance.  
• freezing The phase transition of a substance from a liquid to a solid.  
• frequency A measurement of the number of cycles of a given process per unit of time. The SI unit for measuring frequency is the hertz (Hz), with 1 Hz = 1 cycle per second.  
• galvanic cell A type of battery made up of electrochemicals with two different metals connected by a salt bridge.  
• gas chromatography A type of chromatography commonly used in analytical chemistry to isolate and analyze chemical compounds that can be vaporized without decomposition. Gas chromatography is often used to test the purity of substances, to identify unknown substances, and to measure the relative amounts of the different components of mixtures.  
• gas One of the four fundamental states of matter, characterized by high-energy particles which fill their container but have no definite shape or volume.  
• geochemistry The study of the chemistry and chemical composition of the Earth and geological processes.  
• gram-atom One gram-atom of an element is defined as a collection of 6.023X10^23 atoms.  
• ground glass joint An apparatus designed to quickly and easily fit two pieces of leak-tight glassware together, featuring ground glass surfaces and typically a custom-made conical taper.  
• group Also family. A vertical column of the periodic table of the elements and the elements that share it. Contrast period.  
• hadron A subatomic particle of a type including the baryons and mesons that can take part in the strong interaction.
• halogen Any of the five non-metallic elements of Group 17 of the periodic table: fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At).  
• heat of fusion See enthalpy of fusion.
• heat Energy transferred from one system to another by thermal interaction.  
• hydrate Any substance that contains water or its constituent elements, or any compound formed by the addition of water or its elements to another molecule.  
• hydrogen bond A form of electrostatic interaction between an electronegative atom and a hydrogen atom bound to a second electronegative atom. Hydrogen bonding is unique because the small size of the hydrogen atoms permits proximity of the interacting electrical charges, and may occur as an intermolecular or intramolecular force.  
• hydrolysis The cleavage of a chemical bond by the addition of water.  
• ideal gas constant Also universal gas constant. The proportionality constant in the ideal gas law, defined as 0.08206 L·atm/(K·mol).  
• ideal gas law A chemical law which states that the volume of a gas is proportional to the amount of gas and its Kelvin temperature and inversely proportional to its pressure.  
• ideal solution A solution for which the gas phase exhibits thermodynamic properties analogous to those of a mixture of ideal gases.  
• indicator A special compound added to a solution that changes color depending on the acidity of the solution. Different indicators have different colors and are effective within different pH ranges.  
• induced radioactivity radioactivity caused by bombarding a stable isotope with elemental particles, forming a radioactive isotope  
• inorganic chemistry The branch of chemistry concerning the chemical properties and reactions of inorganic compounds. Contrast organic chemistry.  
• inorganic compound Any chemical compound that does not contain carbon, though there are exceptions. Contrast organic compound.  
• insulator Any material that resists the flow of an electric current. Contrast conductor.  
• intensive property A physical quantity whose value does not depend on the size of the system or the quantity of matter for which it is measured. Examples include density, temperature, and pressure. Contrast extensive property.  
• ion A molecule that has gained or lost one or more electrons from its neutral state and therefore possesses a negative or positive electric charge.  
• ionic bond An electrostatic attraction between oppositely charged ions. [[]]   An ionic bond between a sodium atom (Na) and a fluorine atom (F). The sodium atom loses its sole valence electron (leaving the atom with a positive electrical charge), and the fluorine atom gains this same electron via an exothermic process (giving the atom a negative electrical charge). The oppositely charged ions are then attracted to each other to form a new compound called sodium fluoride.  
• ionization The breaking up of a chemical compound into separate ions.  
• isoelectronicity The phenomenon of two or more chemical species (atoms, molecules, ions, etc.) being composed of different elements but having the same number of valence electrons and the same structural arrangement (i.e. the same number of atoms with the same connectivity). Isoelectronic species typically show useful consistency and predictability in their chemical properties.  
• isomers Ions or molecules with identical chemical formulas but distinct structures or spatial arrangements. Isomers do not necessarily share similar properties. The two main types of isomers are structural isomers and stereoisomers.  
• isotope A variant of a particular chemical element which differs in the number of neutrons present in the nucleus. All isotopes of a given element have the same number of protons in each atom.  
• joule (J) The SI unit of energy (symbol: J). One joule is defined as one Newton-meter.  
• kelvin (K) The SI base unit of temperature (symbol: K). The Kelvin scale is an absolute thermodynamic temperature scale that uses absolute zero as its null point.  
• ketone An organic compound with a carbonyl group between two carbon atoms. [[]]   The skeletal formula for a generic ketone, with R and R' denoting variable carbon-containing substituent groups  
• kinetic energy The energy of an object due to its motion.  
• kinetics A subfield of chemistry specializing in reaction rates.  
• lanthanides Also lanthanoids. The periodic series of metallic elements with atomic numbers 57 through 71, from lanthanum through lutetium.  
• lattice The unique arrangement of atoms or molecules in a crystalline liquid or solid.  
• leveling effect The effect of a solvent on the chemical properties of acids or bases which are dissolved in the solvent. The strength of a strong acid is limited or "leveled" by the basicity of the solvent, and likewise the strength of a strong base is limited by the acidity of the solvent, such that the effective pH of the solution is higher or lower than might be suggested by the acid's or base's dissociation constant.  
• ligand An ion, functional group, or other molecule that binds to a central metal atom to form a coordination complex. Such bonding can range from covalent to ionic, but generally involves formal donation of one or more of the ligand's electron pairs to the metal.  
• light Also referred to as visible light. The portion of the electromagnetic spectrum which is visible to the unaided human eye.  
• liquid One of the four fundamental states of matter, characterized by nearly incompressible fluid particles that retain a definite volume but no fixed shape.  
• malleability See ductility.  
• manometer An instrument used to measure pressure invented by Evangelista Torricelli in 1643.  
• mass number (A) Also atomic mass number or nucleon number. The total number of protons and neutrons (together known as nucleons) within the nucleus of an atom. It determines the atomic mass of the atom. Mass number varies between different isotopes of the same chemical element, and is often included either after the element's name (as in carbon-12) or as a superscript to the left of the element's symbol (as in 12C) to identify a specific isotope.  
• mass spectrometry (MS) An analytical technique that measures the mass-to-charge ratio of ions in a chemical sample by bombarding the sample with electrons to the point of ionization and then separating the charged fragments by subjecting them to an electric or magnetic field, typically in order to determine the elemental or isotopic signatures of an unknown substance, the masses of its constituent particles, and/or the identities or structures of the molecules within it. The results are presented as a mass spectrum, a plot of the intensity of ion signals as a function of the mass-to-charge ratio.  
• mass A property of physical matter that is a measure of its resistance to acceleration when a net force is applied. The SI base unit for mass is the kilogram (kg).  
• matter Any substance that has mass and takes up space by having volume.  
• melting point Also liquefaction point. The temperature at which a substance changes state from a solid to a liquid. It depends on pressure and is usually specified for a given substance under standard conditions. The melting point of a substance is identical to its freezing point.  
• melting The phase transition of a substance from a solid to a liquid.  
• metal Any chemical element which is a good conductor of both electricity and heat and which readily forms cations and ionic bonds with non-metals.  
• metalloid A chemical element or substance possessing properties of both metals and non-metals.  
• methylene blue A heterocyclic aromatic compound with the molecular formula C16H18N3SCl.  
• microcentrifuge tube A small plastic, sealable container that is used to store small volumes of liquid, generally less than 2 milliliters. [[]]   A 1.7-milliliter microcentrifuge tube or Eppendorf tube containing Coomassie Blue solution  
• mixture A material made up of two or more different substances which are mixed physically but are not combined chemically (i.e. a chemical reaction has not taken place which has changed the molecules of the substances into new substances).  
• moiety Any named characteristic group, branch, or other part of a large molecule that may be identified within other kinds of molecules as well. Functional groups are typically smaller and more generic than moieties, whereas substituents and side chains may often be classified as moieties and vice versa.  
• molality Also molal concentration. A measure of the concentration of a solute in a solution in terms of the amount of the solute per unit mass of the solvent. Molality is typically expressed in units of moles per kilogram (mol/kg); a solution with a concentration of exactly 1 mol/kg is sometimes said to be 1 molal. Contrast molarity.  
• molar concentration Also molarity, amount concentration, or substance concentration. A measure of the concentration of a chemical species, especially of a solute in a solution, in terms of the amount of the species per unit volume of solution. Molarity is typically expressed in units of moles per litre (mol/L); a solution with a concentration of exactly 1 mol/L is commonly said to be 1 molar, symbolized as 1 M. Contrast molality.  
• molar fraction Also mole fraction.  
• mole (mol) A unit (symbol: mol) that measures the amount of a substance in terms of the absolute number of particles or entities composing the substance. A single mole contains approximately 6.022×1023 particles or entities.  
• molecular orbital (MO) Any region in which one or more electrons may be found in a molecule (as opposed to that within an individual atom).  
• molecule A number of atoms that are chemically bonded together and collectively electrically neutral.  
• monatomic Having only one atom, as opposed to a molecule composed of more than one. Virtually all elements are monatomic in the gas phase at sufficiently high temperatures. Contrast diatomic and polyatomic.  
• neat Conditions with a liquid reagent or gas performed with no added solvent or cosolvent.  
• neutron A type of subatomic particle that is electrically neutral, having no net charge.  
• noble gas Also inert gas. Any of the six non-metallic elements of Group 18 of the periodic table: helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn). All of the noble gases have outer electron shells that are completely filled in their naturally occurring states, giving them very low chemical reactivity.  
• non-metal Any chemical element which is not a metal.  
• nuclear chemistry The branch of chemistry that studies the various processes and properties relevant to atomic nuclei, including radioactivity.  
• nuclear magnetic resonance spectroscopy A technique that exploits the magnetic properties of certain nuclei, useful for identifying unknown compounds. Nuclear magnetic resonance is often abbreviated NMR.  
• nuclear Of or pertaining to the atomic nucleus.  
• nucleon Either a proton or a neutron, considered in its role as a component of an atomic nucleus.  
• nucleophile Any atom or molecule which can donate an electron pair to another atom or molecule. All molecules or ions with a free pair of electrons or at least one pi bond can act as nucleophiles, by which they are attracted to electron-deficient regions of other species; a chemical reaction involving a nucleophile donating an electron pair to an electrophile may be referred to as nucleophilic attack. Because they donate electrons, nucleophiles are Lewis bases by definition.  
• nucleus The centre of an atom, made up of neutrons and protons and possessing a net positive electric charge.  
• nuclide A species of atom characterized by its mass number, atomic number, and nuclear energy state, provided that the mean life in that state is long enough to be observable.  
• number density A measure of the concentration of countable objects (atoms, molecules, etc.) in space, expressed as the number per unit volume.
• octet rule Also Lewis octet rule. A classical rule for describing the electron configuration of atoms in certain molecules: the maximum number of electron pairs that can be accommodated in the valence shell of an element in the first row of the periodic table is four (or eight total electrons). For elements in the second and subsequent rows, there are many exceptions to this rule.  
• olefin A trivial (non-IUPAC) name for any alkene.  
• orbital Any region of an atom or molecule in which one or more electrons can be found. The term may refer to either an atomic orbital or a molecular orbital.  
• organic acid Any organic compound with acidic properties. Contrast organic base.  
• organic base Any organic compound with basic properties. Contrast organic acid.  
• organic chemistry The branch of chemistry concerned with the chemical properties and reactions of organic compounds. Contrast inorganic chemistry.  
• organic compound Any chemical compound that contains one or more carbon atoms. Contrast inorganic compound.  
• other metal Any of the metallic elements in the p-block, which are characterized by having a combination of relatively low melting points (all less than 950 K) and relatively high electronegativity values (all more than 1.6, revised Pauling).  
• oxidation state Also oxidation number. 1.  The degree of oxidation of an individual atom in a chemical compound, measured as the decrease in the number of electrons relative to the atom's naturally occurring elemental state.2.  The hypothetical electric charge (positive, negative, or zero) that an atom would have if all bonds to atoms of different elements were 100% ionic, with no covalent component.  
• oxoacid Also oxyacid or oxacid. 1.  Any acid having oxygen in the acidic group.2.  Any compound which contains oxygen, at least one other element, and at least one hydrogen atom bound to oxygen, and which produces a conjugate base by the loss of positive hydrogen ions.  
• pH A logarithmic scale used to specify the acidity or basicity of an aqueous solution. The pH scale approximates the negative of the base-10 logarithm of the molar concentration of hydrogen ions in a solution. At room temperature, pure water is neutral (pH = 7); solutions with a pH less than 7 are acidic and those with a pH greater than 7 are basic.  
• paraffin 1.  A trivial (non-IUPAC) name for any alkane.2.  Another name for kerosene.  
• period A horizontal row of the periodic table of the elements and the elements that share it. Contrast group.  
• periodic table of the elements Also simply called the periodic table. A tabular arrangement of the [[chemical elements organized by their atomic number, electron configuration, and other chemical properties, whose adopted structure shows periodic trends and is used by chemists to derive relationships between various elements as well as predict the properties and behaviors of undiscovered or newly synthesized elements. The first periodic table of the elements was published by Russian chemist Dmitri Mendeleev in 1869. [[]]   The modern periodic table of the elements. The horizontal rows are called periods and the vertical columns are called groups or families.  
• phase transition 1.  A transformation of a chemical substance between solid, liquid, and gaseous states of matter and, in rare cases, plasma.2.  The measurable values of the external conditions at which such a transformation occurs. [[]]   This diagram shows the nomenclature commonly used for each of the different phase transitions  
• phase A region of space throughout which all physical properties of a substance are essentially uniform, or a region of material that is chemically uniform, physically distinct, and often mechanically separable. The term phase may have several different uses in chemistry contexts; colloquially, it is often used interchangeably with state of matter, but many distinct phases may exist within a single state of matter.  
• photon A carrier of electromagnetic radiation of all wavelengths (such as gamma rays and radio waves).  
• physical chemistry The branch of chemistry that studies chemical systems in terms of the principles, practices, and concepts of physics, such as motion, energy, force, time, thermodynamics, chemical equilibrium, and statistical mechanics, among others. In contrast to chemical physics, physical chemistry is predominantly (though not entirely) a macroscopic science that studies the physical and chemical interactions of bulk quantities of matter.  
• pipette Also spelled pipet. A laboratory tool commonly used in chemistry, biology, and medicine to transfer and dispense a precisely measured volume of liquid.  
• plasma One of the four fundamental states of matter, in which very high-energy particles are partially or fully ionized to the point that they display unique properties and behaviors unlike those of the other three states. Plasma does not exist freely on the Earth's surface under natural conditions.  
• polyatomic ion A molecule composed of two or more covalently bonded atoms which collectively bear a net electric charge and therefore act as an ion.  
• polyatomic Composed of two or more atoms, of the same or different elements. Contrast monatomic and diatomic.  
• potential energy The stored energy in a body or in a system due to its position in a force field or due to its configuration.
• precipitate The formation of a solid in a solution or inside another solid during a chemical reaction or by diffusion in a solid.  
• precision How close the results of multiple experimental trials or observations are to each other. Compare accuracy.  
• pressure The force applied perpendicular to the surface of an object per unit area. The SI unit for pressure is the pascal (Pa), though many other units of pressure are also commonly used in chemistry.  
• proton A subatomic particle with a positive electric charge that is found in the nucleus of an atom. Often denoted with the symbol H+.  
• protonation The addition of a proton (H+) to an atom, molecule, or ion.
• pure substance See chemical substance.
• pyrolysis The thermal decomposition of materials at elevated temperatures in an inert atmosphere such as a vacuum gas.  
• quantum mechanics The study of how atoms, molecules, subatomic particles, etc. behave and are structured.  
• quark An elementary particle and a fundamental constituent of matter.  
• racemate An equimolar mixture of a pair of enantiomers which does not exhibit optical activity. The chemical name or formula of a racemate is distinguished from those of the enantiomers by the prefix (±)- or by the symbols RS and SR.  
• radiation Energy released in the form of waves or subatomic particles when there is a change from high-energy to low-energy states.  
• radical Also free radical. Any atom, molecule, or ion that has at least one unpaired valence electron. With few exceptions, such unpaired electrons make radicals highly chemically reactive, and therefore organic radicals are usually short-lived.  
• radioactive decay The process of an unstable atomic nucleus losing energy by emitting radiation.  
• rate equation Also rate law.  
• reactant Sometimes used interchangeably with reagent. Any substance that is consumed in the course of a chemical reaction.  
• reaction mechanism The step-by-step sequence of elementary reactions by which a larger chemical reaction or overall change occurs. A complete mechanism must describe and explain which bonds are broken and which are formed (and in what order), as well as all reactants, products, and catalysts involved; the amounts of each; all intermediates, activated complexes, and transition states; and the stereochemistry of each chemical species. Because the detailed processes of a complex reaction are not observable in most cases, a reaction mechanism is often a theoretical conjecture based on thermodynamic feasibility and what little support can be gained from experiment.  
• reaction rate The speed at which reactants are converted into products in a chemical reaction.    
• reactive intermediate Also simply called an intermediate.  
• reactivity series Also activity series. An empirical, calculated, and structurally analytical progression of a series of metals, arranged by their general reactivity from highest to lowest and used to summarize information about their reactions with acids and water and the methods used to extract them from ores.  
• reagent Also another name for a reactant. A test substance that is added to a system in order to bring about a chemical reaction, or to see whether a reaction occurs.    
• retort A laboratory apparatus used for the distillation or dry distillation of chemical substances, traditionally consisting of a spherical vessel with a long, downward-pointing neck that conducts the condensed vapors produced by distillation into a separate collection vessel.
• s-block The collective name for the elements in Groups 1 and 2 of the periodic table (the alkali and alkaline metals), as well as hydrogen and helium.  
• saline solution A common term for a solution of sodium chloride (NaCl) dissolved in water (H2O).  
• salt bridge A device used to connect reduction with oxidation half-cells in an electrochemical cell.  
• salt Any ionic compound composed of one or more anions and one or more cations.  
• semiconductor An electrically conductive solid whose degree of conductivity lies somewhere between that of a conductor and that of an insulator.  
• side chain A chemical substituent group that is attached to the core part or "backbone" of a larger molecule, especially an oligomeric or polymeric hydrocarbon chain that branches off of the longer primary chain of a macromolecule, as used in biochemistry and organic chemistry.  
• single bond A bond that involves the sharing of one pair of electrons.  
• sol A suspension of solid particles in a liquid. Artificial examples include sol-gels.  
• solid One of the four fundamental states of matter, characterized by relatively low-energy particles packed closely together in rigid structures with definite shape and volume. See Young's modulus.  
• solubility The property of a solid, liquid, or gaseous solute to dissolve in a solid, liquid, or gaseous solvent. It is typically expressed as the proportion of solute dissolved in the solvent in a saturated solution.  
• solute The part of a solution that is dissolved into the solvent. For example, sodium chloride (NaCl) is the solute in a solution of saline water.  
• solution A homogeneous mixture made up of multiple substances generally referred to as solutes and solvents.  
• solvation See dissolution.    
• solvent The part of a solution that dissolves the solute. For example, water (H2O) is the solvent in a solution of saline water.  
• spectrometry See mass spectrometry.  
• spectroscopy The study of radiation and matter, such as X-ray absorption and emission spectroscopy.  
• standard conditions of temperature and pressure (STP) A standardisation of ambient temperature and pressure used in order to easily compare experimental results. Standard temperature is 25 degrees Celsius (°C) and standard pressure is 100.000 kilopascals (kPa). Standard conditions are often denoted with the abbreviation STP or SATP.  
• state of matter The condition of matter existing in a distinct, homogeneous, macroscopic form. Solid, liquid, gas, and plasma are the four traditional states of matter and the most well-known. See also phase.  
• stereoisomer Also spatial isomer. An isomer which possesses an identical chemical composition but which differs in the spatial arrangement of its atoms.  
• stoichiometry The calculation of quantities of reactants and products in chemical reactions. Stoichiometry is based on the law of conservation of mass and the observation that quantities of reactants and products typically exist in ratios of positive integers, implying that if the amounts of the separate reactants are known, then the amounts of the products can be calculated. 
• structural isomer Also constitutional isomer.  
• subatomic particle Any particle that is smaller than an atom. Examples include protons, neutrons, and electrons.  
• sublimation The phase transition of a substance from a solid to a limewater fuel or gas without an apparent intervening transition to a liquid in the process.
• substance See chemical substance.  
• suspension A heterogeneous mixture that contains solid particles which are sufficiently large for sedimentation to occur, by which such particles separate from and settle out of the fluid over time if left undisturbed. In a suspension, the solute does not dissolve but remains dispersed or suspended throughout the fluid solvent only transiently and with mechanical agitation. Contrast colloid and solution.  
• temperature A proportional measure of the average kinetic energy of the random motions of the constituent microscopic particles of a system. The SI base unit for temperature is the kelvin.  
• theoretical yield See yield.    
• thermal conductivity The property of a material that allows it to conduct thermal energy or heat (a quantity often denoted by k).  
• thermochemistry The study of the absorption or release of heat during a chemical reaction.  
• thermodynamic stability The condition of a system being in its lowest energy state with its environment (equilibrium).  
• thermodynamics The study of the effects of changing temperature, volume or pressure (or work, heat, and energy) on a macroscopic scale.  
• thermometer An instrument used to measure temperature.  
• titration Also titrimetry or volumetric analysis. A laboratory method of quantitative chemical analysis that is used to determine the concentration of an identified analyte. The procedure involves preparing a particular reagent as a standard solution of known concentration and volume (called the titrant or titrator) and allowing it to react with a solution of the analyte (called the titrand) to determine the latter's concentration.  
• torr A unit for measuring pressure, equivalent to 133.322 Pa or 1.3158×10−3 atm.  
• transition metal An element whose atoms naturally occur with incompletely filled "d" sub-shells. These elements are grouped as the so-called d-block elements in the periodic table.  
• transuranic element Any element with an atomic number greater than 92 (i.e. occurring after uranium in the periodic table). None of the transuranic elements are stable in natural conditions.  
• triple bond A bond that involves the covalent sharing of three pairs of electrons (for example, the diatomic nitrogen molecule, N2, is composed of two nitrogen atoms linked by a triple bond).  
• triple point The place where temperature and pressure of three phases are the same. Water has a special phase diagram. [[]]   A phase diagram showing the triple point and critical point of a substance  
• uncertainty principle Knowing the location of a particle makes the momentum uncertain, while knowing the momentum of a particle makes the location uncertain.
• uncertainty The notion that any measurement that involves estimation of any amount cannot be exactly reproducible.  
• unified atomic mass unit (u) Also Dalton (Da). A unit of mass approximately equal to the mass of one proton or neutron. It is sometimes equated with the technically distinct and obsolete atomic mass unit and abbreviated amu.  
• unit cell The smallest repeating unit of a crystalline lattice.  
• unit factor Statements used in converting between units.  
• vacuum flask Also Dewar flask or thermos. A storage vessel consisting of two flasks or other containers, placed one within the other and joined at the neck, and a space in between that is partially evacuated of air, creating a near-vacuum that significantly reduces the transfer of heat between the vessel's interior and its ambient environment. Vacuum flasks can greatly lengthen the time over which their contents remain warmer or cooler than the ambient environment.  
• valence bond theory A theory explaining the chemical bonding within molecules by discussing valencies, the number of chemical bonds formed by an atom.  
• valence electron Any of the outermost electrons of an atom, which are located in electron shells.  
• valency The combining capacity of an element.  
• van 't Hoff factor The ratio of moles of particles in solution to moles of solute dissolved.  
• van der Waals force One of the forces (attraction/repulsion) between molecules.  
• vapor pressure Also equilibrium vapor pressure. The pressure exerted by a vapor which is in thermodynamic equilibrium with its condensed phases (solid or liquid) at a given temperature in a closed system. It is commonly described as the tendency of particles to spontaneously escape from the liquid or solid state into the gaseous state and is used as an indication of a liquid's evaporation rate.  
• vapor When a substance is below the critical temperature while in the gas phase.  
• vaporization Also boiling. The phase transition of a substance from a liquid to a gas.  
• viscosity A measure of the resistance of a liquid to flow.  
• volatility A material quality which describes how readily a substance vaporizes. At a given temperature and pressure, a substance with high volatility is more likely to exist as a gas, while a substance with low volatility is more likely to exist as a liquid or solid; equivalently, less volatile substances will more readily condense from a gaseous state than highly volatile ones.  
• volt (V) A derived unit of electric potential, electric potential difference, and electromotive force, defined as one joule of work per coulomb.  
• voltmeter An instrument that measures electrical cell potential.  
• volume The quantity of three-dimensional space enclosed by a closed surface, or the space that a substance (solid, liquid, gas, or plasma) or shape occupies or contains. The SI unit for volume is the cubic metre (m3).  
• volumetric analysis See titration.  
• watch glass A circular, concave piece of glass commonly used in chemistry laboratories as a working surface for various purposes, such as evaporating liquids, holding solids while they are being weighed, heating small amounts of a substance, or as a cover for a beaker.  
• water A polar inorganic compound with the chemical formula H2O that is a tasteless, odorless, and generally colorless liquid at standard temperature and pressure, though it also occurs naturally as a solid and a gas at the Earth's surface. It is the most abundant substance on Earth and therefore an integral component of virtually all chemical and biological systems. Water is often described as the "universal solvent" for its inherent ability to dissolve many substances.  
• wave function A mathematical function describing the position of an electron in a three-dimensional space.  
• wet chemistry Also bench chemistry or classical chemistry. A form of analytical chemistry which uses classical laboratory methods such as simple observation and elementary chemical tests to study chemicals and chemical reactions, i.e. without the use of sophisticated instruments or automated or computerized analysis. It is often used in schools to teach the principles of chemistry to students.    
• work-up The series of manipulations required to isolate and purify the desired product or products of a chemical reaction.  
• yield The quantifiable amount of product produced during a chemical reaction.
• zinc A metallic chemical element with atomic number 30 and symbol Zn.
• zone melting A way to remove impurities from an element by melting it and slowly travel down an ingot (cast).  
• zwitterion A chemical compound whose net charge is zero and hence is electrically neutral. But there are some positive and negative charges in it, due to the formal charge, owing to the partial charges of its constituent atoms.  

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External links

IUPAC Compendium of Chemical Terminology