D
d block
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Columns 3 through 12 of the periodic table, containing elements in which the d atomic orbitals are being filled.
Dalton's law
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The statement that the total pressure of a mixture of gases is equal to the sum of the partial pressures of the component gases.
decay constant
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A rate constant for radioactive decay or other first-order decomposition reaction.
degenerate orbital
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One of two or more orbitals having the same energy.
degree of ionization
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The extent to which species in solution ionize. Often applied to the dissociation reactions of acids and bases.
deionized water
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Water that has been passed through ion exchange resin to remove impurities that are ionic.
deliquescent
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Absorbing moisture from the air so readily as to dissolve in the absorbed water to form a solution.
delocalized molecular orbital
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A molecular orbital that encompasses more than two atoms.
denaturation
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Chemical or physical forces acting upon a protein so as to disrupt its secondary and tertiary structure. The biological activity of the protein is lost.
density
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The ratio of the mass of a material to its volume.
deoxyribonucleic acid
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The macromolecules that constitute the genetic material of chromosomes; abbreviated DNA.
deposition
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The process of forming a solid from a gas.
deuterium
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The isotope of hydrogen having one neutron in its nucleus.
dextrorotatory
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Descriptive of a substance that rotates the plane of polarized light to the right.
diagonal relationship
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Similarities in chemical or physical properties found between one element (or its compounds) and another element and found in the periodic table either above and to the left or below and to the right of the first element.
dialysis
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A process in which ions or small molecules in a solution pass through a semipermeable membrane while larger molecules remain behind.
diamagnetic
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Describing a substance containing no unpaired electrons that is repelled by a magnetic field.
diastereomer
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One of two or more compounds that have the same chemical composition and that have the same atoms joined to each other, but that are not mirror images of each other.
diatomic
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Containing two atoms per molecule.
differential rate equation
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An equation that describes the rate of a reaction as a function of the concentrations of reactants (and products), also called rate law.
differentiating solvent
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A solvent that is a sufficiently weak base or acid that the acid or base strength of a pair of substances may differentiated in that solvent.
diffusion
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The spreading of a material into another (usually a gas or liquid).
dilution
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The addition of solvent to a solution (or mixture) to decrease the concentration of a solute (or component).
dimensional analysis
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A technique in which the cancelling of units is used as a tool to check the correctness of a calculation.
dimer
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A molecule formed by the combination of two smaller identical units.
dipolar force
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The attraction between polar molecules as a result of the partially positively charged portion of one molecule being oriented toward the partially negatively charged portion of another molecule.
dipole
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An overall electrically neutral species having separated, equal positive and negative charges; such a species tends to assume certain orientations more than others in an electric field.
dipole moment
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The separation of electrical charge in a molecule that makes the molecule polar.
diprotic
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Describing an acid which can donate two hydrogen ions ("protons") to a base.
disintegration
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The event of a nuclear transformation caused by radioactive decay or nuclear bombardment.
dispersion force
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Intermolecular forces arising from an instantaneous dipole in one molecule inducing a dipole in another molecule.
disproportionation
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A reaction in which a substance undergoes both oxidation and reduction.
dissociation
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The breaking apart of one species into two or more smaller species; often applied to an acid as it forms hydrogen ion and its conjugate base and to the ionization of an electrolyte.
distillation
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A technique for separating the components of a liquid by vaporizing a portion of the liquid and condensing its vapor.
DNA
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Abbreviation for deoxyribonucleic acid; the macromolecules that constitute the genetic material of chromosomes.
double bond
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The sharing of two pairs of electrons between bonded atoms to form a strong linkage between the atoms.
dry ice
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Frozen carbon dioxide; called dry because of its tendency to sublime (form a gas without first forming a liquid).
ductile
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Able to be drawn into a wire.
dynamic equilibrium
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A self-establishing state reached when opposing reactions occur at the same rate - any change moving the system from equilibrium will be opposed, and the system will return to equilibrium if possible.
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