Chemistry Dictionary Terminology "D"

Chemistry Dictionary

Terminology "D"

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D

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Daughter Nuclide

Nuclide that is produced in a nuclear decay.

Debye

The unit used to express dipole moments.

Degenerate

Of the same energy.

Delocalization

Of electrons; refers to bonding electrons that are distributed among more than two atoms that are bonded together; occurs in species that exhibit resonance.

The formation of a set of molecular orbitals that extend over more than two atoms; important in species that valence bond theory describes in terms of resonance.

Denaturation

A process pertaining to a change in structure of a protein form regular to irregular arrangement of the polypeptide chains.

Denatured

A commercial term used to describe ethanol that has been rendered unfit for human consumption because of the addition of harmful ingredients to make it sales tax-expempt.

Density

Mass per unit Volume: D=MV

Deposition

The direct solidification of a vapor by cooling; the reverse of sublimation.

Derivative

A compound that can be imagined to arise from a partent compound by replacement of one atom with another atom or group of atoms. Used extensively in orgainic chemistry to assist in identifying compounds.

Dermal toxicity

Adverse health effects resulting from skin exposure ot a substance.

Designated area

An area that may be used for work with carcinogens, reproductive toxins, or substances that have a high degree of acute toxicity. A designated area may be the entire laboratory, an area of a laboratory, or a device such as a loboratory hood.

Detergent

A soap-like emulsifer that contains a sulfate, SO₃ or a phosphate group instead of a carboxylate group.

Deuterium

An isotope of hydrogen whose atoms are twice as massive as ordinary hydrogen;deuterion atoms contain both a proton and a neutron in the nucleus.

Dextrorotatory

Refers to an optically active substance that rotates the plane of plane polarized light clockwise; also called dextro.

Diagonal Similarities

Refers to chemical similarities in the Periodic Table of elements of Period 2 to elements of Period 3 one group to the right; especially evident toward the left of the periodic table.

Diamagnetism

Weak repulsion by a magnetic field.

Differential Scanning Calorimetry (DSC)

A technique for measuring the temperature, direction, and magnitude of thermal transitions in a sample material by heating/cooling and comparing the amount of energy required to maintain its rate of temperature increase or decrease with an inert reference material under similar conditions.

Differential Thermal Analysis (DTA)

A technique for observing the temperature, direction, and magnitude of thermally induced transitions in a material by heating/cooling a sample and comparing its temperature with that of an inert reference material under similar conditions.

Differential Thermometer

A thermometer used for accurate measurement of very small changes in temperature.

Dilution

Process of reducing the concentration of a solute in solution, usually simply by mixing with more solvent.

Dimer

Molecule formed by combination of two smaller (identical) molecules.

Dipole

Refers to the separation of charge between two covalently bonded atoms

Dipole-dipole Interactions

Attractive interactions between polar molecules, that is, between molecules with permanent dipoles.

Dipole Moment

The product of the distance separating opposite charges of equal magnitude of the charge; a measure of the polarity of a bond or molecule; a measured dipole moment refers to the dipole moment of an entire molecule.

Dispersing Medium

The solvent-like phase in a colloid.

Dispersed Phase

The solute-like species in a colloid.

Displacement Reactions

Reactions in which one element displaces another from a compound.

Disproportionation Reactions

Redox reactions in which the oxidizing agent and the reducing agent are the same species.

Dissociation

In aqueous solution, the process in which a solid ionic compound separates into its ions.

Dissociation Constant

Equilibrium constant that applies to the dissociation of a comples ion into a simple ion and coordinating species (ligands).

Distilland

The material in a distillation apparatus that is to be distilled.

Distillate

The material in a distillation apparatus that is collected in the receiver.

Distillation

The separation of a liquid mixture into its components on the basis of differences in boiling points.

The process in which components of a mixture are separated by boiling away the more volitile liquid.

Domain

A cluster of atoms in a ferromagnetic substance, all of which align in the same direction in the presence of an external magnetic field.

Donor Atom

A ligand atom whose electrons are shared with a Lewis acid.

D-Orbitals

Beginning in the third energy level, aset of five degenerate orbitals per energy level, higher in energy than s and p orbitals of the same energy level.

Dosimeter

A small, calibrated electroscope worn by laboratory personnel and designated to detect and measure incident ionizing radiation or chemical exposure.

Double Bond

Covalent bond resulting from the sharing of four electrons (two pairs) between two atoms.

Double Salt

Solid consisting of two co-crystallized salts.

Doublet

Two peaks or bands of about equal intensity appearing close together on a spectrogram.

Downs Cell

Electrolytic cell for the commercial electrolysis of molten sodium chloride.

For further information see Electrochemistry or Fuel Cells

DP number

The degree of polymerization; the average number of monomer units per polymer unit.

Dry Cells

Ordinary batteries (voltaic cells) for flashlights. radios, and so on; many are Leclanche cells.

For further information see Electrochemistry or Fuel Cells

D -Transition elements (metals)

B Group elements except IIB in the periodic table; sometimes called simply transition elements EX. Fe, Ni, Cu, Ti .

For further information see Metals

Dumas Method

A method used to determine the molecular weights of volatile liquids.

Dynamic Equilibrium

An equilibrium in which processes occur continuously, with no net change.

When two (or more) processes occur at the same rate so that no net change occurs.