JonyC/ScienceGlossary · Datasets at Hugging Face

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compton rule	Chemistry	1	An empirical law of physical chemistry which states that the heat of fusion of a given element multiplied by its atomic weight and then divided by its melting point in kelvin is always equal to approximately 2.
concentration	Chemistry	1	The quantity or abundance of a constituent of a mixture per unit quantity of that mixture; e.g. the amount, in moles, of a dissolved solute per unit volume of a solution, a measure known as molar concentration or molarity. Several different definitions of concentration are widely used in chemistry, including molar concentration, mass concentration, and volume concentration.
condensation	Chemistry	1	A change of molecular state where gas becomes liquid due to cooling.
condosity	Chemistry	1	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).
conductivity	Chemistry	1	See electrical conductivity and thermal conductivity.
conductor	Chemistry	1	Any object or material that allows the flow of an electric current in one or more directions. Contrast insulator.
conformation	Chemistry	1	The spatial arrangement of atoms affording distinction between stereoisomers which can be interconverted by rotations about formally single bonds.
conjugated system	Chemistry	1	A molecule that contains double or triple bonds separated by one single bond; e.g. the compound buta-1,3-diene, with the chemical structure H2C=CH−CH=CH2, has conjugated double bonds. In such molecules, there is some delocalization of electrons in the pi orbitals between the carbon atoms linked by the single bond.
constitutional isomer	Chemistry	1	See structural isomer.
constitutional unit	Chemistry	1	An atom or group of atoms (including pendant atoms or groups, if any) comprising part of the structure of a macromolecule, oligomer, polymer, block, or chain.
cooling curve	Chemistry	1	A line graph representing the change between different phases of matter, typically from a gas to a solid or a liquid to a solid, as a function of time and temperature; e.g. showing how the temperature of a liquid substance changes over time as it condenses below its freezing point.
coordinate covalent bond	Chemistry	1	See dipolar bond.
coordination complex	Chemistry	1	A chemical compound consisting of a central atom or ion, usually metallic and known as the coordination center, bonded to a surrounding array of other groups of atoms, e.g. molecules or ions, which are known as ligands or complexing agents. Many metal-containing compounds, especially those of the transition metals, are coordination complexes. See also complex.
corrosion	Chemistry	1	An irreversible interfacial chemical reaction of a material, especially a metal, with its environment, which results in consumption of the material or dissolution into the material of an external component of the environment.
coulomb	Chemistry	1	The SI unit of electric charge, defined as the charge transported by a constant current of one ampere in one second.
c	Chemistry	1	The SI unit of electric charge, defined as the charge transported by a constant current of one ampere in one second.
counterion	Chemistry	1	The ion that is the counterpart to an oppositely charged ion in a dissociated ionic species; the cation that pairs with a given anion, or vice versa. For example, Na+ is the counterion to Cl−, and vice versa, in solutions of sodium chloride (NaCl).
covalent bond	Chemistry	1	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.
critical point	Chemistry	1	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.
crucible	Chemistry	1	A ceramic or metal dish or other vessel in which substances can be melted or otherwise subjected to very high temperatures.
crystal	Chemistry	1	A solid whose constituent particles (such as atoms, ions, or molecules) are arranged in an orderly periodic microscopic structure, forming a lattice with definite geometry that extends in all directions. Such materials are often described as crystalline.
crystallization point	Chemistry	1	See freezing point.
crystallography	Chemistry	1	The branch of chemistry concerned with the study of crystalline solids, including determining their structure and properties.
cuvette	Chemistry	1	A type of small container used in spectroscopy experiments, usually made of plastic, glass, or quartz and designed to hold a sample (typically a liquid) for measurement inside a spectrometer. Cuvettes should be as clean and transparent as possible to minimize interference with the beams of light on which spectroscopic techniques rely.
dalton	Chemistry	1	A unit of mass defined as 1⁄12 of the mass of a free unexcited atom of carbon-12 at rest. It is approximately equal to the mass of one nucleon.
da	Chemistry	1	A unit of mass defined as 1⁄12 of the mass of a free unexcited atom of carbon-12 at rest. It is approximately equal to the mass of one nucleon.
dalton's law of partial pressures	Chemistry	1	An empirical law which states that in a mixture of non-reacting gases, the total pressure exerted by all of the gases combined is equal to the sum of the partial pressures exerted by each gas individually.
dative bond	Chemistry	1	See dipolar bond.
debye	Chemistry	1	A non-SI unit of measurement of electric dipole moment, defined as 10−18 statcoulomb-centimetres. See also electric dipole moment.
d	Chemistry	1	A non-SI unit of measurement of electric dipole moment, defined as 10−18 statcoulomb-centimetres. See also electric dipole moment.
deionization	Chemistry	1	The removal of ions from a solution by any method. In the case of water, this typically refers to mineral ions such as sodium, iron, and calcium.
deliquescence	Chemistry	1	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	Chemistry	1	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	Chemistry	1	An intensive property of a substance defined as mass per unit volume and expressed by the equation d = m/V.
denticity	Chemistry	1	The number of donor groups in a single ligand that bind to a central atom in a coordination complex.
deposition	Chemistry	1	The settling of particles within a solution or mixture.
depression of freezing point	Chemistry	1	See freezing-point depression.
desiccant	Chemistry	1	A hygroscopic substance used to induce or sustain a state of dryness or desiccation (i.e. the absence of moisture) in its vicinity by abstracting water molecules from other substances. Desiccants come in many different forms and work by many different principles, ranging from simple absorption to the chemical bonding of water molecules.
deuterium	Chemistry	1	One of two stable isotopes of a hydrogen atom, the nucleus of which contains one proton and one neutron. Deuterium is both heavier and much less abundant in nature than the other stable isotope, known as protium (1H).
deuteron	Chemistry	1	The nucleus of a deuterium atom (an isotope of hydrogen), containing one proton and one neutron.
dewar flask	Chemistry	1	See vacuum flask.
dianion	Chemistry	1	A compound or molecular entity bearing exactly two negative charges, which may be located on a single atom or on different atoms, or may be delocalized.
diatomic	Chemistry	1	Composed of two atoms, of the same or different elements. Contrast monatomic and polyatomic.
diatomic molecule	Chemistry	1	Any molecule composed of only two atoms, of the same or different elements.
diffusion	Chemistry	1	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.
dilatant	Chemistry	1	A substance with the ability to increase in volume when its shape is changed.
dimer	Chemistry	1	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.
dipolar bond	Chemistry	1	A type of covalent bond formed by the coordination of two or more electrically neutral moieties, the combination of which results in a charge-separated molecule or coordination complex, in which two electrons deriving from the same atom are shared between the donor atom and an acceptor atom, creating an internal two-center molecular dipole moment.
dipole	Chemistry	1	The electric or magnetic separation of electric charge into a pair of charges of equal magnitude but opposite sign, one positively charged and one negatively charged, separated by some typically small distance.
dipole moment	Chemistry	1	See electric dipole moment, magnetic dipole moment, molecular dipole moment, bond dipole moment, electron electric dipole moment, electron magnetic dipole moment, and nuclear magnetic moment.
dispersion	Chemistry	1	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.
dissociation	Chemistry	1	Any process by which a polyatomic molecule or molecular entity (e.g. an ionic compound or coordination complex), or an aggregate of molecular entities, separates or splits into two or more molecules, atoms, ions, radicals, or other constituents, usually in a reversible manner. Examples include unimolecular heterolysis and homolysis, the dissolution of salts, and acid dissociation. Contrast association.
dissolution	Chemistry	1	The interaction of a solvent with the molecules or ions of a solute, involving bond formation, hydrogen bonding, and van der Waals forces.
distillation	Chemistry	1	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	Chemistry	1	A bond involving the covalent sharing of two pairs of electrons.
double salt	Chemistry	1	1. A salt composed of more than one different cation or anion, or which upon hydrolysis forms two different cations and anions.
dropping point	Chemistry	1	The temperature at which a grease changes from a semi-solid to a liquid state under standardized conditions, i.e. the upper limit at which the grease retains its structure, though not necessarily the maximum temperature at which it can be used.
dry box	Chemistry	1	A chamber or container in which the interior is maintained at very low humidity, often by filling it with argon or with air lacking carbon dioxide, in order to provide an inert atmosphere in which manipulation of very reactive chemicals or moisture-sensitive procedures can be carried out in the laboratory.
drying agent	Chemistry	1	See desiccant.
ductility	Chemistry	1	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.
dystectic mixture	Chemistry	1	A mixture of two or more substances which has the highest melting point of all possible mixtures of these substances. Contrast eutectic mixture.
earth metal	Chemistry	1	See alkaline earth metal.
ebullition	Chemistry	1	See boiling.
effective molecular diameter	Chemistry	1	The physical extent of the electron cloud surrounding a molecule of a particular gas, as calculated in any of several ways and usually expressed in nanometres or ångströms.
effervescence	Chemistry	1	The escape of gas from an aqueous solution without the application of heat, and the bubbling, foaming, or fizzing that results; e.g. the release of carbon dioxide from carbonated water.
electric charge	Chemistry	1	A measured property (coulombs) that determines electromagnetic interaction.
electric dipole moment	Chemistry	1	A measure of the separation of positive and negative electric charges within an electrical system, i.e. a measure of the system's overall electrical polarity. The SI unit for measuring electric dipole moment is the coulomb-metre (C⋅m), but the debye (D), a non-SI unit, is also widely used in chemistry and atomic physics.
electride	Chemistry	1	An ionic compound for which the anion is an electron.
electrochemical cell	Chemistry	1	A device capable of either generating electrical energy from chemical reactions, in which case it is known as a galvanic or voltaic cell, or using electrical energy to cause chemical reactions, in which case it is known as an electrolytic cell. For example, a battery contains one or more galvanic cells, each of which consists of two electrodes arranged such that an oxidation–reduction reaction produces an electromotive force.
electrochemistry	Chemistry	1	A branch of physical chemistry concerned with the relationship between electrical potential difference and identifiable chemical change, as understood through either the chemical reactions accompanying the passage of an electric current or the potential difference that results from a particular chemical reaction.
electrolyte	Chemistry	1	A solution that conducts a certain amount of electric current and can be split categorically into weak and strong electrolytes.
electromagnetic radiation	Chemistry	1	A type of wave that can go through vacuums as well as material and is classified as a self-propagating wave.
electromagnetism	Chemistry	1	Fields with an electric charge and electrical properties that change the way that particles move and interact.
electron	Chemistry	1	A type of subatomic particle with a net charge that is negative. Contrast positron.
electron capture	Chemistry	1	A type of nuclear transformation by which the proton-rich nucleus of an electrically neutral atom absorbs or 'captures' an electron from one of its own inner shells, often those closest to the nucleus, which provokes a reaction that results in a nuclear proton changing into a neutron accompanied by the simultaneous emission of an electron neutrino.
electron configuration	Chemistry	1	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 electric dipole moment	Chemistry	1	An intrinsic property of an electron such that its potential energy is linearly related to the strength of its electric field; a measure of the distribution of an electron's negative charge within the electric field it creates. See also electric dipole moment.
de	Chemistry	1	An intrinsic property of an electron such that its potential energy is linearly related to the strength of its electric field; a measure of the distribution of an electron's negative charge within the electric field it creates. See also electric dipole moment.
electron magnetic dipole moment	Chemistry	1	The magnetic moment of an electron, caused by the intrinsic properties of its spin and electric charge, equal to approximately −9.284764×10−24 joules per tesla.
electron pair	Chemistry	1	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	Chemistry	1	An orbital around the nucleus of an atom which contains a fixed number of electrons (usually two or eight).
electronegativity	Chemistry	1	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.
χ	Chemistry	1	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	Chemistry	1	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	Chemistry	1	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	Chemistry	1	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.
elution	Chemistry	1	The process of extracting one material from another by washing with a solvent. Elution works by running a solution containing an analyte past an adsorbent matrix designed to selectively bind the analyte molecules, and subsequently washing the adsorbent/analyte complex with a solvent, known as an eluent. The solvent molecules displace the analyte by binding to the adsorbent in its place, allowing the analyte, now part of the eluate, to be carried out of the complex and into a collector for analysis.
empirical formula	Chemistry	1	The simplest whole-number ratio of the atoms of each element present in a chemical compound.
emulsion	Chemistry	1	A stable mixture of two liquids (like oil and water) where one liquid is suspended in tiny droplets in the other.
end-group	Chemistry	1	A constitutional unit that occupies a terminal position within or is at an extremity of a macromolecule or polymer, and thus by definition is connected to only one other constitutional unit of the molecule.
energy	Chemistry	1	A system's ability to do work.
enplethy	Chemistry	1	See amount of substance.
enthalpy	Chemistry	1	A measure of the total internal energy of a thermodynamic system, usually symbolized by H.
entropy	Chemistry	1	The amount of energy that is not available for work in a closed thermodynamic system, usually symbolized by S.
enzyme	Chemistry	1	A complex protein that acts as a catalyst (speeds up chemical reactions) in specific biochemical reactions. For example, saliva contains an enzyme called amylase that can break down starch into simple sugars.
eppendorf tube	Chemistry	1	A generalized and trademarked name used to refer to a microcentrifuge tube.
equilibrium	Chemistry	1	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 in a reacting system have stopped changing in time.
equimolar	Chemistry	1	Having an equal number of moles, or solutions of equal molar concentration.
ester	Chemistry	1	A class of organic and inorganic compounds derived from the reaction of an acid with an alcohol, in which at least one hydroxyl group (–OH) is replaced by an alkoxy group (–O–). Esters have the general formula RCO2R′, where R and R' represent any alkyl or aryl group.
ether	Chemistry	1	A class of organic compounds and a functional group containing an oxygen atom connected to two alkyl or aryl groups, which may be the same or different. Ethers have the general formula R–O–R′, where R and R′ represent the alkyl or aryl groups.

compton rule

Chemistry

1

An empirical law of physical chemistry which states that the heat of fusion of a given element multiplied by its atomic weight and then divided by its melting point in kelvin is always equal to approximately 2.

concentration

Chemistry

1

The quantity or abundance of a constituent of a mixture per unit quantity of that mixture; e.g. the amount, in moles, of a dissolved solute per unit volume of a solution, a measure known as molar concentration or molarity. Several different definitions of concentration are widely used in chemistry, including molar concentration, mass concentration, and volume concentration.

condensation

Chemistry

1

A change of molecular state where gas becomes liquid due to cooling.

condosity

Chemistry

1

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).

conductivity

Chemistry

1

See electrical conductivity and thermal conductivity.

conductor

Chemistry

1

Any object or material that allows the flow of an electric current in one or more directions. Contrast insulator.

conformation

Chemistry

1

The spatial arrangement of atoms affording distinction between stereoisomers which can be interconverted by rotations about formally single bonds.

conjugated system

Chemistry

1

A molecule that contains double or triple bonds separated by one single bond; e.g. the compound buta-1,3-diene, with the chemical structure H2C=CH−CH=CH2, has conjugated double bonds. In such molecules, there is some delocalization of electrons in the pi orbitals between the carbon atoms linked by the single bond.

constitutional isomer

Chemistry

1

See structural isomer.

constitutional unit

Chemistry

1

An atom or group of atoms (including pendant atoms or groups, if any) comprising part of the structure of a macromolecule, oligomer, polymer, block, or chain.

cooling curve

Chemistry

1

A line graph representing the change between different phases of matter, typically from a gas to a solid or a liquid to a solid, as a function of time and temperature; e.g. showing how the temperature of a liquid substance changes over time as it condenses below its freezing point.

coordinate covalent bond

Chemistry

1

See dipolar bond.

coordination complex

Chemistry

1

A chemical compound consisting of a central atom or ion, usually metallic and known as the coordination center, bonded to a surrounding array of other groups of atoms, e.g. molecules or ions, which are known as ligands or complexing agents. Many metal-containing compounds, especially those of the transition metals, are coordination complexes. See also complex.

corrosion

Chemistry

1

An irreversible interfacial chemical reaction of a material, especially a metal, with its environment, which results in consumption of the material or dissolution into the material of an external component of the environment.

coulomb

Chemistry

1

The SI unit of electric charge, defined as the charge transported by a constant current of one ampere in one second.

c

Chemistry

1

The SI unit of electric charge, defined as the charge transported by a constant current of one ampere in one second.

counterion

Chemistry

1

The ion that is the counterpart to an oppositely charged ion in a dissociated ionic species; the cation that pairs with a given anion, or vice versa. For example, Na+ is the counterion to Cl−, and vice versa, in solutions of sodium chloride (NaCl).

covalent bond

Chemistry

1

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.

critical point

Chemistry

1

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.

crucible

Chemistry

1

A ceramic or metal dish or other vessel in which substances can be melted or otherwise subjected to very high temperatures.

crystal

Chemistry

1

A solid whose constituent particles (such as atoms, ions, or molecules) are arranged in an orderly periodic microscopic structure, forming a lattice with definite geometry that extends in all directions. Such materials are often described as crystalline.

crystallization point

Chemistry

1

See freezing point.

crystallography

Chemistry

1

The branch of chemistry concerned with the study of crystalline solids, including determining their structure and properties.

cuvette

Chemistry

1

A type of small container used in spectroscopy experiments, usually made of plastic, glass, or quartz and designed to hold a sample (typically a liquid) for measurement inside a spectrometer. Cuvettes should be as clean and transparent as possible to minimize interference with the beams of light on which spectroscopic techniques rely.

dalton

Chemistry

1

A unit of mass defined as 1⁄12 of the mass of a free unexcited atom of carbon-12 at rest. It is approximately equal to the mass of one nucleon.

da

Chemistry

1

A unit of mass defined as 1⁄12 of the mass of a free unexcited atom of carbon-12 at rest. It is approximately equal to the mass of one nucleon.

dalton's law of partial pressures

Chemistry

1

An empirical law which states that in a mixture of non-reacting gases, the total pressure exerted by all of the gases combined is equal to the sum of the partial pressures exerted by each gas individually.

dative bond

Chemistry

1

See dipolar bond.

debye

Chemistry

1

A non-SI unit of measurement of electric dipole moment, defined as 10−18 statcoulomb-centimetres. See also electric dipole moment.

d

Chemistry

1

A non-SI unit of measurement of electric dipole moment, defined as 10−18 statcoulomb-centimetres. See also electric dipole moment.

deionization

Chemistry

1

The removal of ions from a solution by any method. In the case of water, this typically refers to mineral ions such as sodium, iron, and calcium.

deliquescence

Chemistry

1

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

Chemistry

1

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

Chemistry

1

An intensive property of a substance defined as mass per unit volume and expressed by the equation d = m/V.

denticity

Chemistry

1

The number of donor groups in a single ligand that bind to a central atom in a coordination complex.

deposition

Chemistry

1

The settling of particles within a solution or mixture.

depression of freezing point

Chemistry

1

See freezing-point depression.

desiccant

Chemistry

1

A hygroscopic substance used to induce or sustain a state of dryness or desiccation (i.e. the absence of moisture) in its vicinity by abstracting water molecules from other substances. Desiccants come in many different forms and work by many different principles, ranging from simple absorption to the chemical bonding of water molecules.

deuterium

Chemistry

1

One of two stable isotopes of a hydrogen atom, the nucleus of which contains one proton and one neutron. Deuterium is both heavier and much less abundant in nature than the other stable isotope, known as protium (1H).

deuteron

Chemistry

1

The nucleus of a deuterium atom (an isotope of hydrogen), containing one proton and one neutron.

dewar flask

Chemistry

1

See vacuum flask.

dianion

Chemistry

1

A compound or molecular entity bearing exactly two negative charges, which may be located on a single atom or on different atoms, or may be delocalized.

diatomic

Chemistry

1

Composed of two atoms, of the same or different elements. Contrast monatomic and polyatomic.

diatomic molecule

Chemistry

1

Any molecule composed of only two atoms, of the same or different elements.

diffusion

Chemistry

1

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.

dilatant

Chemistry

1

A substance with the ability to increase in volume when its shape is changed.

dimer

Chemistry

1

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.

dipolar bond

Chemistry

1

A type of covalent bond formed by the coordination of two or more electrically neutral moieties, the combination of which results in a charge-separated molecule or coordination complex, in which two electrons deriving from the same atom are shared between the donor atom and an acceptor atom, creating an internal two-center molecular dipole moment.

dipole

Chemistry

1

The electric or magnetic separation of electric charge into a pair of charges of equal magnitude but opposite sign, one positively charged and one negatively charged, separated by some typically small distance.

dipole moment

Chemistry

1

See electric dipole moment, magnetic dipole moment, molecular dipole moment, bond dipole moment, electron electric dipole moment, electron magnetic dipole moment, and nuclear magnetic moment.

dispersion

Chemistry

1

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.

dissociation

Chemistry

1

Any process by which a polyatomic molecule or molecular entity (e.g. an ionic compound or coordination complex), or an aggregate of molecular entities, separates or splits into two or more molecules, atoms, ions, radicals, or other constituents, usually in a reversible manner. Examples include unimolecular heterolysis and homolysis, the dissolution of salts, and acid dissociation. Contrast association.

dissolution

Chemistry

1

The interaction of a solvent with the molecules or ions of a solute, involving bond formation, hydrogen bonding, and van der Waals forces.

distillation

Chemistry

1

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

Chemistry

1

A bond involving the covalent sharing of two pairs of electrons.

double salt

Chemistry

1

1. A salt composed of more than one different cation or anion, or which upon hydrolysis forms two different cations and anions.

dropping point

Chemistry

1

The temperature at which a grease changes from a semi-solid to a liquid state under standardized conditions, i.e. the upper limit at which the grease retains its structure, though not necessarily the maximum temperature at which it can be used.

dry box

Chemistry

1

A chamber or container in which the interior is maintained at very low humidity, often by filling it with argon or with air lacking carbon dioxide, in order to provide an inert atmosphere in which manipulation of very reactive chemicals or moisture-sensitive procedures can be carried out in the laboratory.

drying agent

Chemistry

1

See desiccant.

ductility

Chemistry

1

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.

dystectic mixture

Chemistry

1

A mixture of two or more substances which has the highest melting point of all possible mixtures of these substances. Contrast eutectic mixture.

earth metal

Chemistry

1

See alkaline earth metal.

ebullition

Chemistry

1

See boiling.

effective molecular diameter

Chemistry

1

The physical extent of the electron cloud surrounding a molecule of a particular gas, as calculated in any of several ways and usually expressed in nanometres or ångströms.

effervescence

Chemistry

1

The escape of gas from an aqueous solution without the application of heat, and the bubbling, foaming, or fizzing that results; e.g. the release of carbon dioxide from carbonated water.

electric charge

Chemistry

1

A measured property (coulombs) that determines electromagnetic interaction.

electric dipole moment

Chemistry

1

A measure of the separation of positive and negative electric charges within an electrical system, i.e. a measure of the system's overall electrical polarity. The SI unit for measuring electric dipole moment is the coulomb-metre (C⋅m), but the debye (D), a non-SI unit, is also widely used in chemistry and atomic physics.

electride

Chemistry

1

An ionic compound for which the anion is an electron.

electrochemical cell

Chemistry

1

A device capable of either generating electrical energy from chemical reactions, in which case it is known as a galvanic or voltaic cell, or using electrical energy to cause chemical reactions, in which case it is known as an electrolytic cell. For example, a battery contains one or more galvanic cells, each of which consists of two electrodes arranged such that an oxidation–reduction reaction produces an electromotive force.

electrochemistry

Chemistry

1

A branch of physical chemistry concerned with the relationship between electrical potential difference and identifiable chemical change, as understood through either the chemical reactions accompanying the passage of an electric current or the potential difference that results from a particular chemical reaction.

electrolyte

Chemistry

1

A solution that conducts a certain amount of electric current and can be split categorically into weak and strong electrolytes.

electromagnetic radiation

Chemistry

1

A type of wave that can go through vacuums as well as material and is classified as a self-propagating wave.

electromagnetism

Chemistry

1

Fields with an electric charge and electrical properties that change the way that particles move and interact.

electron

Chemistry

1

A type of subatomic particle with a net charge that is negative. Contrast positron.

electron capture

Chemistry

1

A type of nuclear transformation by which the proton-rich nucleus of an electrically neutral atom absorbs or 'captures' an electron from one of its own inner shells, often those closest to the nucleus, which provokes a reaction that results in a nuclear proton changing into a neutron accompanied by the simultaneous emission of an electron neutrino.

electron configuration

Chemistry

1

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 electric dipole moment

Chemistry

1

An intrinsic property of an electron such that its potential energy is linearly related to the strength of its electric field; a measure of the distribution of an electron's negative charge within the electric field it creates. See also electric dipole moment.

de

Chemistry

1

An intrinsic property of an electron such that its potential energy is linearly related to the strength of its electric field; a measure of the distribution of an electron's negative charge within the electric field it creates. See also electric dipole moment.

electron magnetic dipole moment

Chemistry

1

The magnetic moment of an electron, caused by the intrinsic properties of its spin and electric charge, equal to approximately −9.284764×10−24 joules per tesla.

electron pair

Chemistry

1

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

Chemistry

1

An orbital around the nucleus of an atom which contains a fixed number of electrons (usually two or eight).

electronegativity

Chemistry

1

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.

χ

Chemistry

1

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

Chemistry

1

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

Chemistry

1

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

Chemistry

1

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.

elution

Chemistry

1

The process of extracting one material from another by washing with a solvent. Elution works by running a solution containing an analyte past an adsorbent matrix designed to selectively bind the analyte molecules, and subsequently washing the adsorbent/analyte complex with a solvent, known as an eluent. The solvent molecules displace the analyte by binding to the adsorbent in its place, allowing the analyte, now part of the eluate, to be carried out of the complex and into a collector for analysis.

empirical formula

Chemistry

1

The simplest whole-number ratio of the atoms of each element present in a chemical compound.

emulsion

Chemistry

1

A stable mixture of two liquids (like oil and water) where one liquid is suspended in tiny droplets in the other.

end-group

Chemistry

1

A constitutional unit that occupies a terminal position within or is at an extremity of a macromolecule or polymer, and thus by definition is connected to only one other constitutional unit of the molecule.

energy

Chemistry

1

A system's ability to do work.

enplethy

Chemistry

1

See amount of substance.

enthalpy

Chemistry

1

A measure of the total internal energy of a thermodynamic system, usually symbolized by H.

entropy

Chemistry

1

The amount of energy that is not available for work in a closed thermodynamic system, usually symbolized by S.

enzyme

Chemistry

1

A complex protein that acts as a catalyst (speeds up chemical reactions) in specific biochemical reactions. For example, saliva contains an enzyme called amylase that can break down starch into simple sugars.

eppendorf tube

Chemistry

1

A generalized and trademarked name used to refer to a microcentrifuge tube.

equilibrium

Chemistry

1

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 in a reacting system have stopped changing in time.

equimolar

Chemistry

1

Having an equal number of moles, or solutions of equal molar concentration.

ester

Chemistry

1

A class of organic and inorganic compounds derived from the reaction of an acid with an alcohol, in which at least one hydroxyl group (–OH) is replaced by an alkoxy group (–O–). Esters have the general formula RCO2R′, where R and R' represent any alkyl or aryl group.

ether

Chemistry

1

A class of organic compounds and a functional group containing an oxygen atom connected to two alkyl or aryl groups, which may be the same or different. Ethers have the general formula R–O–R′, where R and R′ represent the alkyl or aryl groups.