ChemEd DL Glossary

Glossary extended from the original PTL!

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a
absolute configuration
The spatial arrangement of the atomsThe smallest particle of an element that can be involved in chemical combination with another element; an atom consists of protons and neutrons in a tiny, very dense nucleus, surrounded by electrons, which occupy most of its volume. about a chiralRefers to an ion or molecule that cannot be superimposed on its mirror image. center.
absolute zero
The minimum possible temperatureA physical property that indicates whether one object can transfer thermal energy to another object.: 0 K, -273.15 °C, -459.67 °F.
absorbance
A measure of the quantity of light that does not pass through a sample. AbsorbanceA measure of the quantity of light that does not pass through a sample. Absorbance is the negative lograrithm of the transmittance. Transmittance is the fraction of incident light that passes through a sample. In the visible region of the spectrum, absorbance occurs when a material uses the energy from light to change the energy level of the material's electrons. Because different materials have different electronic energy states, they absorb light of different wavelengths. is the negative lograrithm of the transmittanceThe fraction of incident light that passes through a sample.. Transmittance is the fraction of incident light that passes through a sample. In the visible region of the spectrum, absorbance occurs when a material uses the energyA system's capacity to do work. from light to change the energy level of the material's electrons. Because different materials have different electronic energy states, they absorb light of different wavelengths.
absorption
Permeation of a solidA state of matter having a specific shape and volume and in which the particles do not readily change their relative positions. by a gasA state of matter in which a substance occupies the full volume of its container and changes shape to match the shape of the container. In a gas the distance between particles is much greater than the diameters of the particles themselves; hence the distances between particles can change as necessary so that the matter uniformly occupies its container. or liquidA state of matter in which the atomic-scale particles remain close together but are able to change their positions so that the matter takes the shape of its container, or permeation of a liquid by a gas. AbsorptionPermeation of a solid by a gas or liquid, or permeation of a liquid by a gas. Absorption differs from adsorption in that the substance absorbed is found throughout the absorbent. differs from adsorptionFormation of a layer of gas, liquid, or solid on the surface of a solid; the adsorbed substance is held by either covalent bonds or by non-covalent (intermolecular) forces. Adsorption differ from absorption in that the adsorbed substance is on the surface only. in that the substanceA material that is either an element or that has a fixed ratio of elements in its chemical formula. absorbed is found throughout the absorbent.
absorption spectrum
The quantity of light a sample absorbs (its [[absorbanceA measure of the quantity of light that does not pass through a sample. Absorbance is the negative lograrithm of the transmittance. Transmittance is the fraction of incident light that passes through a sample. In the visible region of the spectrum, absorbance occurs when a material uses the energy from light to change the energy level of the material's electrons. Because different materials have different electronic energy states, they absorb light of different wavelengths.]]) plotted as a function of wavelengthThe distance between the crests of adjacent waves (or between any adjacent corresponding points in waves); used in the context of electromagnetic radiation., frequencyThe rate at which a periodic event occurs; specifically, the rate at which the waves of electromagnetic radiation pass a point., or energyA system's capacity to do work.. An absorption spectrumThe quantity of light a sample absorbs (its [[absorbance]]) plotted as a function of wavelength, frequency, or energy. An absorption spectrum of a substance often can help to identify the substance. of a substanceA material that is either an element or that has a fixed ratio of elements in its chemical formula. often can help to identify the substance.
accuracy
The extent to which an experimental value agrees with true value for a quantity.
acid
In Arrhenius theory, a substanceA material that is either an element or that has a fixed ratio of elements in its chemical formula. that produces hydrogen ions (hydronium ions) in aqueousDescribing a solution in which the solvent is water. solutionA mixture of one or more substances dissolved in a solvent to give a homogeneous mixture.. In Bronsted-Lowry theory, a hydrogen-ion (protonThe positively charged particle in an atomic nucleus; its mass is similar to the mass of a hydrogen atom.) donor. In Lewis theory, a species that accepts a pair of electrons to form a covalent bondThe attractive force between one atom (nucleus and core electrons) and another atom as a result of sharing electrons..
acid ionization constant
The equilibrium constantThe value of the equilibrium constant expression when equilibrium concentrations are substituted; a value greater than one indicates the position of equilibrium lies toward products (product-favored), and a value less than one indicates the position of equilibrium lies toward reactants (reactant-favored). for the ionizationA process in which an atom, molecule, or negative ion loses an electron; a process in which a covalent molecule reacts with a solvent to form positive and negative ions; for example, a weak acid reacting with water to form its conjugate base (an anion) and a hydrogen (hydronium) ion. of a weak acidAn acid that ionizes only partially in a given solvent. to form its conjugate baseThe base formed when an acid releases a hydrogen ion (proton). and hydrogen (hydronium) ions. Also called acid dissociationThe breaking apart of one species into two or more smaller species; often applied to ions in a crystal lattice, which dissociate when the ionic solid dissolves in water. Dissociation refers to separation of particles that already exist; ionization refers to the formation of ions from neutral species, as in the ionization of a weak acid in aqueous solutoin. constant.
acid precipitation
Any form of precipitationThe formation of a solid within a solution, often by the combination of cations and anions to form an insoluble ionic compound. from the atmosphereA unit of pressure equal to 101.325 kPa or 760 mmHg; abbreviated atm. Also, the mixture of gases surrounding the earth. (rain, snow, frost, etc.) that produces water with a pH below 5.6. Usually the acidity comes from sulfur and nitrogen oxides formed by combustionVigorous combination of a material with oxygen gas, usually resulting in a flame. of fossil fuels.
acid rain
Rain with pHA logarithmic measure of the concentration of hydrogen (hydronium) ion; pH = -log10([H+]) or pH = -log10([H3O+]). less than 5.6 (the pH of unpolluted rainwater). Acid rainRain with pH less than 5.6 (the pH of unpolluted rainwater). Acid rain is caused by sulfur and nitrogen oxides formed by combustion of fossil fuels. is caused by sulfur and nitrogen oxides formed by combustionVigorous combination of a material with oxygen gas, usually resulting in a flame. of fossil fuels.
acid-base indicator
A substanceA material that is either an element or that has a fixed ratio of elements in its chemical formula. that changes color depending on the concentrationA measure of the ratio of the quantity of a substance to the quantity of solvent, solution, or ore. Also, the process of making something more concentrated. of hydrogen ions (hydronium ions) in solutionA mixture of one or more substances dissolved in a solvent to give a homogeneous mixture.. An acid-base indicatorA substance that changes color depending on the concentration of hydrogen ions (hydronium ions) in solution. An acid-base indicator is an acid (or a base) whose color is different when protonated from the color when not protonated. is an acidIn Arrhenius theory, a substance that produces hydrogen ions (hydronium ions) in aqueous solution. In Bronsted-Lowry theory, a hydrogen-ion (proton) donor. In Lewis theory, a species that accepts a pair of electrons to form a covalent bond. (or a base) whose color is different when protonated from the color when not protonated.
acidic anhydride
A substanceA material that is either an element or that has a fixed ratio of elements in its chemical formula. (often a non-metalAn element characterized by a glossy surface, high thermal and electrical conductivity, malleability, and ductility. oxide) that reacts with water to form an acidIn Arrhenius theory, a substance that produces hydrogen ions (hydronium ions) in aqueous solution. In Bronsted-Lowry theory, a hydrogen-ion (proton) donor. In Lewis theory, a species that accepts a pair of electrons to form a covalent bond.. Also called acid anhydrideA substance that reacts with water to form an acid or a base. A substance from which water has been removed..
actinide
An elementA substance containing only one kind of atom and that therefore cannot be broken down into component substances by chemical means. in the periodic tableA chart showing the symbols of the elements arranged in order by atomic number and having chemically related elements appearing in columns. from actinium (atomic numberThe number of protons in the nucleus of an atom; used to define the position of an element in the periodic table; represented by the letter Z. 89) to lawrencium (atomic number 103); also called actinoidAn element in the periodic table from actinium (atomic number 89) to lawrencium (atomic number 103); also called actinide. Sometimes actinium itself is not included in this series; sometimes lawrencium is not.. Sometimes actinium itself is not included in this series; sometimes lawrencium is not.
actinoid
An elementA substance containing only one kind of atom and that therefore cannot be broken down into component substances by chemical means. in the periodic tableA chart showing the symbols of the elements arranged in order by atomic number and having chemically related elements appearing in columns. from actinium (atomic numberThe number of protons in the nucleus of an atom; used to define the position of an element in the periodic table; represented by the letter Z. 89) to lawrencium (atomic number 103); also called actinideAn element in the periodic table from actinium (atomic number 89) to lawrencium (atomic number 103); also called actinoid. Sometimes actinium itself is not included in this series; sometimes lawrencium is not.. Sometimes actinium itself is not included in this series; sometimes lawrencium is not.
activated complex
In the mechanism of a reaction, a species that lies at an energyA system's capacity to do work. peak and that can change either into products or into reactants; also called a transition state.
activation energy
The energyA system's capacity to do work. barrier over which a reaction must progress in order for reactants to form products; the minimum energy that reactants must have if they are to be converted to products.
active metal
A highly reactive metalAn element characterized by a glossy surface, high thermal and electrical conductivity, malleability, and ductility., usually an elementA substance containing only one kind of atom and that therefore cannot be broken down into component substances by chemical means. in the first or second column of the periodic tableA chart showing the symbols of the elements arranged in order by atomic number and having chemically related elements appearing in columns..
active site
The location where catalysisThe increase in rate of a reaction due to the presence of a substance that undergoes no net change during the reaction. occurs in an enzymeA highly effective, highly specific biochemical catalyst; usually a protein, but RNA enzymes also exist. or other catalystA substance that increases the rate of a chemical reaction but that undergoes no net change during the reaction..
activity series
A sequence of species arranged according to their reactivity; often used to describe metals and the ease with which they can be oxidized.
actual yield
The quantity of a productA substance produced by a chemical reaction. found to be formed in a chemical reactionA process in which one or more substances, the reactant or reactants, change into one or more different substances, the products; chemical change involves rearrangement, combination, or separation of atoms. Also called chemical change. (distinguished from theoretical yieldThe maximum quantity of a product that could be formed in a chemical reaction if all the limiting reactant reacted to form products (distinguished from actual yield).).
acyl group
The functional groupA set of atoms in a molecule that confer on the molecule a characteristic set of physical and chemical properties. RC(=O)-, formally derived from a carboxylic acidAn organic compound containing the functional group -C(=O)OH. by the removal of the hydroxyl groupThe functional group of an oxygen atom bonded to an hydrogen atom, -OH; found in alcohols..
addition polymer
The kind of polymerA large molecule containing a large number of repeating units; a substance formed from such molecules. that is formed by the combination of monomers without the release of a small moleculeA set of atoms joined by covalent bonds and having no net charge. at each point where monomers are joined.
addition reaction
A reaction in which two moleular-scale species combine to form a single molecular-scale species (distinguished from a substitution reactionA reaction in which one atom or functional group is replaced by another (distinguished from an addition reaction).).
adduct
A species formed by the union of two molecular-scale species held together by a coordinate covalent bondA bond between two atoms in which the shared electrons are considered to be contributed by only one of the atoms..
adhesive force
An intermolecular forceAny attraction between molecules, including dipolar attractions, hydrogen bonds, and London forces. between unlike molecules, usually occurring where two phases meet.
adsorption
Formation of a layer of gasA state of matter in which a substance occupies the full volume of its container and changes shape to match the shape of the container. In a gas the distance between particles is much greater than the diameters of the particles themselves; hence the distances between particles can change as necessary so that the matter uniformly occupies its container., liquidA state of matter in which the atomic-scale particles remain close together but are able to change their positions so that the matter takes the shape of its container, or solidA state of matter having a specific shape and volume and in which the particles do not readily change their relative positions. on the surface of a solid; the adsorbed substanceA material that is either an element or that has a fixed ratio of elements in its chemical formula. is held by either covalent bonds or by non-covalent (intermolecular) forces. AdsorptionFormation of a layer of gas, liquid, or solid on the surface of a solid; the adsorbed substance is held by either covalent bonds or by non-covalent (intermolecular) forces. Adsorption differ from absorption in that the adsorbed substance is on the surface only. differ from absorptionPermeation of a solid by a gas or liquid, or permeation of a liquid by a gas. Absorption differs from adsorption in that the substance absorbed is found throughout the absorbent. in that the adsorbed substance is on the surface only.
alcohol
An organicRefers to the branch of chemistry that studies compounds containing carbon, usually in combination with hydrogen and other elements such as O, N, S, and P. Certain small ions and compounds containing carbon (such as carbonate ions and carbon dioxide) are not considered to be organic, but rather are classed as inorganic. compoundA substance made up of two or more elements and having those elements present in definite proportions; a compound can be decomposed into two or more different substances. containing the functional groupA set of atoms in a molecule that confer on the molecule a characteristic set of physical and chemical properties. -OH.
aldehyde
An organicRefers to the branch of chemistry that studies compounds containing carbon, usually in combination with hydrogen and other elements such as O, N, S, and P. Certain small ions and compounds containing carbon (such as carbonate ions and carbon dioxide) are not considered to be organic, but rather are classed as inorganic. compoundA substance made up of two or more elements and having those elements present in definite proportions; a compound can be decomposed into two or more different substances. containing the functional groupA set of atoms in a molecule that confer on the molecule a characteristic set of physical and chemical properties. -CHO.
alicyclic
An aliphaticA hydrocarbon whose molecules contain no aromatic rings; for example, an alkane, alkene, or alkyne. compoundA substance made up of two or more elements and having those elements present in definite proportions; a compound can be decomposed into two or more different substances. containing one or more rings of carbon atomsThe smallest particle of an element that can be involved in chemical combination with another element; an atom consists of protons and neutrons in a tiny, very dense nucleus, surrounded by electrons, which occupy most of its volume..
aliphatic
A hydrocarbonA compound containing only the elements carbon and hydrogen. whose molecules contain no aromaticReferring to a hydrocarbon containing benzene-like rings and exhibiting characteristic stability and patterns of reactivity. rings; for example, an alkaneA hydrocarbon containing only single bonds between carbon atoms., alkeneA hydrocarbon containing one or more double bonds between carbon atoms. Also called olefin., or alkyneA hydrocarbon containing one or more triple bonds between carbon atoms..
alkali
Any substanceA material that is either an element or that has a fixed ratio of elements in its chemical formula. in aqueousDescribing a solution in which the solvent is water. solutionA mixture of one or more substances dissolved in a solvent to give a homogeneous mixture. that is bitter, irritating to the skin, and has a pHA logarithmic measure of the concentration of hydrogen (hydronium) ion; pH = -log10([H+]) or pH = -log10([H3O+]). value greater than 7.0.
alkali metal
One of the metals appearing in the first column of the periodic tableA chart showing the symbols of the elements arranged in order by atomic number and having chemically related elements appearing in columns..
alkaline earth
One of the metals appearing in the second column of the periodic tableA chart showing the symbols of the elements arranged in order by atomic number and having chemically related elements appearing in columns..
alkaloid
A naturally occurring organicRefers to the branch of chemistry that studies compounds containing carbon, usually in combination with hydrogen and other elements such as O, N, S, and P. Certain small ions and compounds containing carbon (such as carbonate ions and carbon dioxide) are not considered to be organic, but rather are classed as inorganic. baseIn Arrhenius theory, a substance that increases the concentration of hydroxide ions in an aqueous solution. In Bronsted-Lowry theory, a hydrogen-ion (proton) acceptor. In Lewis theory, a species that donates a pair of electrons to form a covalent bond. containing nitrogen.
alkane
A hydrocarbonA compound containing only the elements carbon and hydrogen. containing only single bonds between carbon atomsThe smallest particle of an element that can be involved in chemical combination with another element; an atom consists of protons and neutrons in a tiny, very dense nucleus, surrounded by electrons, which occupy most of its volume..
alkene
A hydrocarbonA compound containing only the elements carbon and hydrogen. containing one or more double bonds between carbon atomsThe smallest particle of an element that can be involved in chemical combination with another element; an atom consists of protons and neutrons in a tiny, very dense nucleus, surrounded by electrons, which occupy most of its volume.. Also called olefinA hydrocarbon containing one or more double bonds between carbon atoms. Also called alkene..
alkyl group
A functional groupA set of atoms in a molecule that confer on the molecule a characteristic set of physical and chemical properties. formally derived from an alkaneA hydrocarbon containing only single bonds between carbon atoms. by the removal of a hydrogen atomThe smallest particle of an element that can be involved in chemical combination with another element; an atom consists of protons and neutrons in a tiny, very dense nucleus, surrounded by electrons, which occupy most of its volume..
alkyne
A hydrocarbonA compound containing only the elements carbon and hydrogen. containing one or more triple bonds between carbon atomsThe smallest particle of an element that can be involved in chemical combination with another element; an atom consists of protons and neutrons in a tiny, very dense nucleus, surrounded by electrons, which occupy most of its volume..
allotrope
One of two or more different structural forms for an elementA substance containing only one kind of atom and that therefore cannot be broken down into component substances by chemical means. that exist in the same physical state at the same temperatureA physical property that indicates whether one object can transfer thermal energy to another object. and pressureForce per unit area; in gases arising from the force exerted by collisions of gas molecules with the wall of the container..
alloy
A solidA state of matter having a specific shape and volume and in which the particles do not readily change their relative positions. that has metallic properties and is made up of two or more elements.
alpha particle
A species consisting of two protons and two neutrons and formed by radioactiveDescribes a substance that gives off radiation‐alpha particles, beta particles, or gamma rays‐by the disintegration of its nucleus. decay or nuclear bombardment; identical in composition to the nucleusThe collection of protons and neutrons at the center of an atom that contains nearly all of the atoms's mass. of a helium-4 atomThe smallest particle of an element that can be involved in chemical combination with another element; an atom consists of protons and neutrons in a tiny, very dense nucleus, surrounded by electrons, which occupy most of its volume..
amalgam
An alloyA solid that has metallic properties and is made up of two or more elements. (metallic solutionA mixture of one or more substances dissolved in a solvent to give a homogeneous mixture.) containing mercury.
amide
An organicRefers to the branch of chemistry that studies compounds containing carbon, usually in combination with hydrogen and other elements such as O, N, S, and P. Certain small ions and compounds containing carbon (such as carbonate ions and carbon dioxide) are not considered to be organic, but rather are classed as inorganic. compoundA substance made up of two or more elements and having those elements present in definite proportions; a compound can be decomposed into two or more different substances. formally derived from a carboxylic acidAn organic compound containing the functional group -C(=O)OH. by the replacement of the hydroxyl groupThe functional group of an oxygen atom bonded to an hydrogen atom, -OH; found in alcohols. by -NH2, -NHR, or -NR2.
amide linkage
A chemical bond linkage formed when a carboxylic acidAn organic compound containing the functional group -C(=O)OH. reacts with an amineAn organic compound formally derived from ammonia by the replacement of one or more hydrogen atoms by alkyl groups. Examples are primary amine: RNH2; secondary amine: R2NH; tertiary amine: R3N., often found in polymers such as nylonAny of several human-made polyamide fibers; polyamides are formed by condensation of an amine group with a carboxylic acid group. and proteins; in proteins also called a peptide bondThe amide linkage that joins the carboxylic acid end of one amino acid with the amine end of another amino acid to form a peptide or protein..
amine
An organicRefers to the branch of chemistry that studies compounds containing carbon, usually in combination with hydrogen and other elements such as O, N, S, and P. Certain small ions and compounds containing carbon (such as carbonate ions and carbon dioxide) are not considered to be organic, but rather are classed as inorganic. compoundA substance made up of two or more elements and having those elements present in definite proportions; a compound can be decomposed into two or more different substances. formally derived from ammonia by the replacement of one or more hydrogen atomsThe smallest particle of an element that can be involved in chemical combination with another element; an atom consists of protons and neutrons in a tiny, very dense nucleus, surrounded by electrons, which occupy most of its volume. by alkyl groups. Examples are primary amineAn organic compound formally derived from ammonia by the replacement of one or more hydrogen atoms by alkyl groups. Examples are primary amine: RNH2; secondary amine: R2NH; tertiary amine: R3N.: RNH2; secondary amine: R2NH; tertiary amine: R3N.
amino acid
A carboxylic acidAn organic compound containing the functional group -C(=O)OH. containing an amino groupThe functional group of a nitrogen atom bonded to two hydrogen atoms, -NH2; found in amines and amino acids. (-NH2). In an alpha amino acidA carboxylic acid containing an amino group (-NH2). In an alpha amino acid, the amino group is attached to the carbon atom adjacent to the carboxyl group., the amino group is attached to the carbon atomThe smallest particle of an element that can be involved in chemical combination with another element; an atom consists of protons and neutrons in a tiny, very dense nucleus, surrounded by electrons, which occupy most of its volume. adjacent to the carboxylThe functional group consisting of a carbon atom bonded to a hydroxyl group and doubly bonded to an oxygen atom; found in carboxylic acids: -C(=O)OH. group.
amino group
The functional groupA set of atoms in a molecule that confer on the molecule a characteristic set of physical and chemical properties. of a nitrogen atom bonded to two hydrogen atomsThe smallest particle of an element that can be involved in chemical combination with another element; an atom consists of protons and neutrons in a tiny, very dense nucleus, surrounded by electrons, which occupy most of its volume., -NH2; found in amines and amino acids.
amorphous
A solidA state of matter having a specific shape and volume and in which the particles do not readily change their relative positions. in which the constituent atomsThe smallest particle of an element that can be involved in chemical combination with another element; an atom consists of protons and neutrons in a tiny, very dense nucleus, surrounded by electrons, which occupy most of its volume., molecules, or ions have no long-range repeating structure.
amphiprotic
A moleculeA set of atoms joined by covalent bonds and having no net charge. or ionAn atom or covalently bonded set of atoms that carries an overall net charge. that can both gain a protonThe positively charged particle in an atomic nucleus; its mass is similar to the mass of a hydrogen atom. and lose a proton; that is, a species that can serve as either an Bronsted-Lowry acidA molecule or ion that donates a hydrogen ion (proton) to another molecule or ion. or a Bronsted-Lowry baseA molecule or ion that accepts a hydrogen ion (proton) from another ion or molecule..
amphoteric
A substanceA material that is either an element or that has a fixed ratio of elements in its chemical formula. that can behave as either an acidIn Arrhenius theory, a substance that produces hydrogen ions (hydronium ions) in aqueous solution. In Bronsted-Lowry theory, a hydrogen-ion (proton) donor. In Lewis theory, a species that accepts a pair of electrons to form a covalent bond. or a baseIn Arrhenius theory, a substance that increases the concentration of hydroxide ions in an aqueous solution. In Bronsted-Lowry theory, a hydrogen-ion (proton) acceptor. In Lewis theory, a species that donates a pair of electrons to form a covalent bond.. Examples are aluminum metalAn element characterized by a glossy surface, high thermal and electrical conductivity, malleability, and ductility., aluminum hydroxide, and zinc hydroxide.
amu
Abbreviation for atomic mass unitA unit for expressing the relative masses of atoms; abbreviated amu. An atom of carbon-12 has a mass of 12 amu. 1 amu corresponds to 1.662x10-24 g., a unit for expressing the relative masses of atomsThe smallest particle of an element that can be involved in chemical combination with another element; an atom consists of protons and neutrons in a tiny, very dense nucleus, surrounded by electrons, which occupy most of its volume.. An atom of carbon-12 has a mass of 12 amuAbbreviation for atomic mass unit, a unit for expressing the relative masses of atoms. An atom of carbon-12 has a mass of 12 amu. 1 amu corresponds to 1.662x10-24 g.. 1 amu corresponds to 1.662x10-24 g.
angstrom
A unitA particular measure of a physical quantity that is used to express the magnitude of the physical quantity; for example, the meter is the unit of the physical quantity, length. of length equal to 100 pm or 10-10 m.
anhydride
A substanceA material that is either an element or that has a fixed ratio of elements in its chemical formula. that reacts with water to form an acidIn Arrhenius theory, a substance that produces hydrogen ions (hydronium ions) in aqueous solution. In Bronsted-Lowry theory, a hydrogen-ion (proton) donor. In Lewis theory, a species that accepts a pair of electrons to form a covalent bond. or a baseIn Arrhenius theory, a substance that increases the concentration of hydroxide ions in an aqueous solution. In Bronsted-Lowry theory, a hydrogen-ion (proton) acceptor. In Lewis theory, a species that donates a pair of electrons to form a covalent bond.. A substance from which water has been removed.
anhydrous
Free of water. Often used to describe a solidA state of matter having a specific shape and volume and in which the particles do not readily change their relative positions. having no water of crystallization or a solventThe substance to which a solute is added to make a solution. from which traces of water have been removed.
anion
A negatively charged ionAn atom or covalently bonded set of atoms that carries an overall net charge.. An ion that is attracted toward the anodeThe electrode in an electrochemical cell where oxidation occurs. The positively charged electrode in a vacuum tube. in an electrolytic cellAn electrochemical cell used to drive a reaction that would otherwise be non-spontaneous (reactant-favored)..
anode
The electrodeIn an electrochemical cell, a surface on which oxidation or reduction occurs; an electrode conducts electric current into or out of a cell. in an electrochemical cellA system containing an oxidation-reduction reaction in which oxidation and reduction reactions are physically separated and the transferred electrons pass through an electrical circuit. Voltaic (galvanic) cells produce and electic current; electrolyic cells use electric current to force a reaction to occur. where oxidationThat part of a chemical reaction in which a reactant loses electrons; simultaneous reduction of a reactant must occur. occurs. The positively charged electrode in a vacuum tube.
anodizing
The electrolytic depositionThe process of forming a solid from a gas. of a metalAn element characterized by a glossy surface, high thermal and electrical conductivity, malleability, and ductility. oxide film to serve as a protective or decorative layer; the object to be coated is made the anodeThe electrode in an electrochemical cell where oxidation occurs. The positively charged electrode in a vacuum tube. in an electrolytic cellAn electrochemical cell used to drive a reaction that would otherwise be non-spontaneous (reactant-favored). and its surface is oxidized.
antibonding molecular orbital
An orbitalA mathematically defined region of electron density around one or more atoms; a wave function that defines the properties of a particular electron in an atom or molecule. formed by the overlap of out-of-phase orbitals from two different atomsThe smallest particle of an element that can be involved in chemical combination with another element; an atom consists of protons and neutrons in a tiny, very dense nucleus, surrounded by electrons, which occupy most of its volume.; higher in energyA system's capacity to do work. than the corresponding bonding molecular orbitalAn orbital formed by the overlap of atomic orbitals that are in phase and therefore reinforce each other; lower in energy than an anti-bonding molecular orbital and lower in energy than the average energy of the atomic orbitals from which it is formed..
aqueous
Describing a solutionA mixture of one or more substances dissolved in a solvent to give a homogeneous mixture. in which the solventThe substance to which a solute is added to make a solution. is water.
aromatic
Referring to a hydrocarbonA compound containing only the elements carbon and hydrogen. containing benzene-like rings and exhibiting characteristic stability and patterns of reactivity.
Arrhenius acid
A substanceA material that is either an element or that has a fixed ratio of elements in its chemical formula. that increases the concentrationA measure of the ratio of the quantity of a substance to the quantity of solvent, solution, or ore. Also, the process of making something more concentrated. of hydrogen (hydronium) ions in aqueousDescribing a solution in which the solvent is water. solutionA mixture of one or more substances dissolved in a solvent to give a homogeneous mixture..
Arrhenius acid-base theory
The idea that in aqueousDescribing a solution in which the solvent is water. solutionA mixture of one or more substances dissolved in a solvent to give a homogeneous mixture. acids ionize to produce hydrogen ions and bases ionize to produce hydroxide ions.
Arrhenius base
A substanceA material that is either an element or that has a fixed ratio of elements in its chemical formula. that increases the concentrationA measure of the ratio of the quantity of a substance to the quantity of solvent, solution, or ore. Also, the process of making something more concentrated. of hydroxide ions in aqueousDescribing a solution in which the solvent is water. solutionA mixture of one or more substances dissolved in a solvent to give a homogeneous mixture..
Arrhenius equation
An equation that expresses the logarithmic relationship between the rate constantIn a differential rate equation, the proportionality constant that relates the rate with the concentrations of reactants and other species that affect the rate. The rate constant is the rate of reaction when all concentrations are 1 M. of a reaction and the reciprocal of the absolute temperatureA physical property that indicates whether one object can transfer thermal energy to another object.; ln k = exp(Ea/RT).
atactic
Having no regularly repeating structural units; said of a polymerA large molecule containing a large number of repeating units; a substance formed from such molecules..
atm
Abbreviation for atmosphereA unit of pressure equal to 101.325 kPa or 760 mmHg; abbreviated atm. Also, the mixture of gases surrounding the earth., a unitA particular measure of a physical quantity that is used to express the magnitude of the physical quantity; for example, the meter is the unit of the physical quantity, length. of pressureForce per unit area; in gases arising from the force exerted by collisions of gas molecules with the wall of the container. equal to 101.325 kPa or 760 mmHg.
atmosphere
A unitA particular measure of a physical quantity that is used to express the magnitude of the physical quantity; for example, the meter is the unit of the physical quantity, length. of pressureForce per unit area; in gases arising from the force exerted by collisions of gas molecules with the wall of the container. equal to 101.325 kPa or 760 mmHg; abbreviated atmAbbreviation for atmosphere, a unit of pressure equal to 101.325 kPa or 760 mmHg.. Also, the mixtureA combination of two or more substances in which the substances retain their chemical identity. of gases surrounding the earth.
atom
The smallest particle of an elementA substance containing only one kind of atom and that therefore cannot be broken down into component substances by chemical means. that can be involved in chemical combination with another element; an atomThe smallest particle of an element that can be involved in chemical combination with another element; an atom consists of protons and neutrons in a tiny, very dense nucleus, surrounded by electrons, which occupy most of its volume. consists of protons and neutrons in a tiny, very dense nucleusThe collection of protons and neutrons at the center of an atom that contains nearly all of the atoms's mass., surrounded by electrons, which occupy most of its volume. Synonyms: atoms
atomic force microscope
A type of microscope in which a tiny diamond-chip probe is held on a cantilever in contact with a sample's surface; the probe is scanned slowly across the surface and the force between probe and surfaces is measured and kept constant by adjusting the height of the probe tip. Gives a picture of the surface with molecular-scale resolution.
atomic mass
The average massA measure of the force required to impart unit acceleration to an object; mass is proportional to chemical amount, which represents the quantity of matter in an object. of the naturally occurring isotopes of an elementA substance containing only one kind of atom and that therefore cannot be broken down into component substances by chemical means., taking into account the different natural abundances of the isotopes. Expressed relative to the value of exactly 12 for carbon-12; also called atomic weightThe average mass of the naturally occurring isotopes of an element, taking into account the different natural abundances of the isotopes. Expressed relative to the value of exactly 12 for carbon-12; also called atomic mass..
atomic mass unit
A unitA particular measure of a physical quantity that is used to express the magnitude of the physical quantity; for example, the meter is the unit of the physical quantity, length. for expressing the relative masses of atomsThe smallest particle of an element that can be involved in chemical combination with another element; an atom consists of protons and neutrons in a tiny, very dense nucleus, surrounded by electrons, which occupy most of its volume.; abbreviated amuAbbreviation for atomic mass unit, a unit for expressing the relative masses of atoms. An atom of carbon-12 has a mass of 12 amu. 1 amu corresponds to 1.662x10-24 g.. An atom of carbon-12 has a mass of 12 amu. 1 amu corresponds to 1.662x10-24 g.
atomic number
The number of protons in the nucleusThe collection of protons and neutrons at the center of an atom that contains nearly all of the atoms's mass. of an atomThe smallest particle of an element that can be involved in chemical combination with another element; an atom consists of protons and neutrons in a tiny, very dense nucleus, surrounded by electrons, which occupy most of its volume.; used to define the position of an elementA substance containing only one kind of atom and that therefore cannot be broken down into component substances by chemical means. in the periodic tableA chart showing the symbols of the elements arranged in order by atomic number and having chemically related elements appearing in columns.; represented by the letter Z.
atomic orbital
A mathematical function from which electronA negatively charged, sub-atomic particle with charge of 1.602 x 10-19 coulombs and mass of9.109 x 1023 kilograms; electrons have both wave and particle properties; electrons occupy most of the volume of an atom but represent only a tiny fraction of an atom's mass. densityThe ratio of the mass of a sample of a material to its volume. around an atomThe smallest particle of an element that can be involved in chemical combination with another element; an atom consists of protons and neutrons in a tiny, very dense nucleus, surrounded by electrons, which occupy most of its volume. can be calculated. A region in an atom within which there is a high probability that a particular electron will be found.
atomic spectrum
The quantity of light absorbed or emitted from a sample containing atomsThe smallest particle of an element that can be involved in chemical combination with another element; an atom consists of protons and neutrons in a tiny, very dense nucleus, surrounded by electrons, which occupy most of its volume. measured as a function of wavelengthThe distance between the crests of adjacent waves (or between any adjacent corresponding points in waves); used in the context of electromagnetic radiation., frequencyThe rate at which a periodic event occurs; specifically, the rate at which the waves of electromagnetic radiation pass a point., or energyA system's capacity to do work.. An atomic spectrumThe quantity of light absorbed or emitted from a sample containing atoms measured as a function of wavelength, frequency, or energy. An atomic spectrum can be used to identify an element, even in a distant star. can be used to identify an elementA substance containing only one kind of atom and that therefore cannot be broken down into component substances by chemical means., even in a distant star.
atomic weight
The average massA measure of the force required to impart unit acceleration to an object; mass is proportional to chemical amount, which represents the quantity of matter in an object. of the naturally occurring isotopes of an elementA substance containing only one kind of atom and that therefore cannot be broken down into component substances by chemical means., taking into account the different natural abundances of the isotopes. Expressed relative to the value of exactly 12 for carbon-12; also called atomic massThe average mass of the naturally occurring isotopes of an element, taking into account the different natural abundances of the isotopes. Expressed relative to the value of exactly 12 for carbon-12; also called atomic weight..
aufbau
A scheme for accounting for the electron configurations of elements in which the electronA negatively charged, sub-atomic particle with charge of 1.602 x 10-19 coulombs and mass of9.109 x 1023 kilograms; electrons have both wave and particle properties; electrons occupy most of the volume of an atom but represent only a tiny fraction of an atom's mass. configuration of one element is determined by adding one electron to the electron configuration of the previous element in the periodic tableA chart showing the symbols of the elements arranged in order by atomic number and having chemically related elements appearing in columns..
autoionization
The ionizationA process in which an atom, molecule, or negative ion loses an electron; a process in which a covalent molecule reacts with a solvent to form positive and negative ions; for example, a weak acid reacting with water to form its conjugate base (an anion) and a hydrogen (hydronium) ion. of the molecules of a solventThe substance to which a solute is added to make a solution.; for example, water autoionizes to form hydrogen (hydronium) and hydroxide ions.
Avogadro's constant
The number of atomsThe smallest particle of an element that can be involved in chemical combination with another element; an atom consists of protons and neutrons in a tiny, very dense nucleus, surrounded by electrons, which occupy most of its volume., molecules, ions, or other species per moleThat chemical amount of a substance containing the same number of units as 12 g of carbon-12., defined by the number of carbon atoms in 12 g of carbon-12 and numerically equal to 6.0220 x 1023 mol-1.
Avogadro's hypothesis
The idea that equal volumes of two gases at the same temperatureA physical property that indicates whether one object can transfer thermal energy to another object. and pressureForce per unit area; in gases arising from the force exerted by collisions of gas molecules with the wall of the container. contain equal numbers of molecules.
Avogadro's number
The number of units in a moleThat chemical amount of a substance containing the same number of units as 12 g of carbon-12. of substanceA material that is either an element or that has a fixed ratio of elements in its chemical formula., defined by the number of carbon atomsThe smallest particle of an element that can be involved in chemical combination with another element; an atom consists of protons and neutrons in a tiny, very dense nucleus, surrounded by electrons, which occupy most of its volume. in exactly 12 g of carbon-12 and numerically equal to 6.0220 x 1023.
axial
Oriented along an axis; in a trigonal bipyramidalA molecular shape having the central atom surrounded by a plane of 3 atoms at the corners of a triangle, one atom above the plane, and one atom below. structure, lying above or below the trigonal plane; in chair cyclohexane, bonds perpendicular to the rough plane of the carbon atomsThe smallest particle of an element that can be involved in chemical combination with another element; an atom consists of protons and neutrons in a tiny, very dense nucleus, surrounded by electrons, which occupy most of its volume..
azeotrope
A solutionA mixture of one or more substances dissolved in a solvent to give a homogeneous mixture. of two more substances, usually liquids, that remains unchanged in composition as it boils because the vaporThe gaseous state of a substance that typically exists as a liquid or solid; a gas at a temperature near or below the boiling point of the corresponding liquid. has the same composition as the liquid.