Chemistry Definitions Starting With the Letter D

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This chemistry dictionary offers the chemistry definitions starting with the letter D. These glossary terms are commonly used in chemistry and chemical engineering. Click the letter below to find the terms and definitions beginning with that letter.


D- (prefix) – D- is a prefix added to a enantiomer name that has dextrorotatory properties.

d orbital – A d orbital corresponds to an electron orbital with angular momentum quantum number ℓ = 2.

dalton – A dalton is a unit of mass equal to 112 the mass of a carbon-12 atom. The abbreviation for dalton is amu or u.
1 amu = 1.66053873×10-27 kg
Also known as: atomic mass unit, amu

Dalton’s Law – Dalton’s Law states the total pressure of a mixture of gases is equal to the sum of the partial pressures of the mixture’s component gases.

darmstadtium – Darmstadtium is the name for the transition metal element with atomic number 110 and is represented by the symbol Ds. Darmstadtium was formerly known as ununnilium with symbol Uun.

data – Data is any representation to which meaning can be attached.
Also known as: information
Examples: Characters, numbers, measurements, and words are all data.

dative bond – A dative bond is a covalent bond between two atoms where one of the atoms provides both electrons that form the bond.
Also known as: coordination bond, dipolar bond

daughter atom – A daughter atom refers to the atom that is the product atom formed during the radioactive decay in a nuclear reaction.
Also known as: daughter isotope
Example: When U-238 decays into Th-234, the daughter atom is Th-234.

daughter isotope – Another term for daughter atom. See definition above.

DC or D/C – DC is an acronym for direct current. Direct current refers to a system where current flows in a single direction only.

deaeration – Deaeration is a process where dissolved gasses are removed from a solvent.

de Broglie Equation – The de Broglie equation is an equation used to describe the wave properties of matter. The particle’s wavelength is expressed by the equation
λ = h/mv
where λ is wavelength, h is Planck’s constant, m is the mass of a particle, moving at a velocity v.

de Broglie wavelength – The de Broglie wavelength is the wavelength of the wave associated with a particle. The wavelength is calculated using the de Broglie equation.

Debye – A Debye is a cgs unit for dipole moments. The Debye unit is a defined unit. 4.8 Debye is equal to the dipole moment created when two oppositely charged charges with a magnitude of one electron are separated by one angstrom.
1 Debye (D) = 3.338 x 10-30 Coulomb meters.

Debye temperature – The Debye temperature is the temperature at which the wavelength of vibration of the atoms in a crystal lattice is equal to the length of the unit cell. The Debye temperature is part of the Debye model used to predict the thermodynamic properties of materials, such as specific heat and heat capacity at low temperatures.

deca – Deca is the prefix associated with x10 and is denoted by the symbol da. It is rarely used in metric measurements.

decadic absorbance – Decadic absorbance is a measure of the quantity of light absorbed by a sample.
Also known as: Absorbance, Extinction, Optical Density

decantation – Decantation is a process to separate mixtures. Decanting is done to separate particulates from a liquid by allowing the solids to settle to the bottom of the mixture and pouring off the particle-free part of the liquid. Another method is to allow two immiscible liquids to separate and the lighter liquid is poured off.

decarboxylation – Decarboxylation is a chemical reaction which removes carbon dioxide (CO2) from a substrate. Decarboxylation is the reverse process of carboxylation.

decarboxylayse – A decarboxylase is a lyase which catalyzes a reaction to add or remove a carboxyl group (-COOH) from a compound.
Also known as: carboxy-layse

decay constant – A decay constant is the proportionality constant between the rate of radioactive nuclear decay and the number of radioactive nuclei remaining. Decay constant is often denoted by the Greek letter λ and is equal to the reciprocal of half-life.

decay rate – Decay rate refers to the rate radioactive isotopes decay into their daughter isotopes.

deci – Deci is the prefix associated with x10-1 and is denoted by the symbol d.
Example: A regular can of soda contains 3.5 dL of soda or 350 milliliters.

decoction – Decoction is a process of extracting oils and other compounds from plant material. The material is first crushed or otherwise broken down, then added to water and boiled. After boiling, any remaining material is filtered out, leaving the desired compounds in the water.
Decoction also refers to the remaining liquid from this process.

decomposition reaction – A decomposition reaction is a type of chemical reaction where one reactant yields two or more products. The general form of a decomposition reaction is AB → A + B.
Example: Water can be separated by electrolysis into hydrogen gas and oxygen gas through the decomposition reaction
2 H2O → 2 H2 + O2

deflagration – Deflagration is the chemical process where a substance rapidly and intensely burns. This process is generally faster than combustion but slower than a detonation.
Example: Adding water to burning oil can cause a deflagration. The water rapidly boils to create steam and forces oil droplets to be ejected into the flames adding fuel to the fire.

degenerate orbitals – Degenerate orbitals are two orbitals with different quantum states but have the same energy.

degree – A degree is an increment of measurement. The degree is the general name for incremental temperature measurements.
Example: There are 100 degrees between the freezing point and the boiling point of water in the Celsius scale. There are 180 degrees between the same two points on the Fahrenheit scale.

dehydration reaction – A dehydration reaction is a chemical reaction between two compounds where one of the products is water. Dehydration reactions are also involved in the production of many polymers.
Also known as: condensation reaction
Examples: Reactions that produce acid anhydrides are dehydration reactions. Acetic acid (CH3COOH) forms acetic anhydride ((CH3CO)2O) and water through the dehydration reaction
2 CH3COOH → (CH3CO)2O + H2O.

deionization – Deionization is the removal of ions. The term is generally used with respect to removal of ions from water. Deionization is commonly achieved by passing the water through successive ion exchange columns. In one column, ions are exchanged for H+ ions. In another column, anions are exchanged for OH ions. Following a reaction of H+ with OH ions, no ions remain in solution.

deliquescence – Deliquescence is the process in which a soluble substance picks up water vapor from the air to form a solution. In order for deliquescence to occur, the vapor pressure of the water in the air must be greater than the vapor pressure of the saturated solution.

delocalized electron – A delocalized electron is an electron in an atom, ion or molecule not associated with any single atom or a single covalent bond. Delocalized electrons contribute to the conductivity of the atom, ion or molecule. Materials with many delocalized electrons tend to be highly conductive.

delta bond or δ bond – A delta bond (δ bond for short) is a covalent bond formed from the overlap of four d orbitals between two atoms. Delta bonds are observed in organometallic compounds.

denaturant – A denaturant is an substance that acts as an additive to prevent human consumption.
Example: Benzene is occasionally added as a denaturant to pure alcohol to prevent human consumption.

denature – Denature is the process of altering the natural qualities or removing a characteristic component of a substance. Denature also means to make alcohol unsuitable for consumption by adding unpleasant flavors or toxic chemicals.

denatured alcohol – Denatured alcohol is ethyl alcohol (ethanol or grain alcohol) containing a foul-tasting or toxic chemical, added to make it unfit for human consumption. Common additives include acetone and methanol, both toxic to humans. Denatured alcohol is used for lab experiments, to make rubbing alcohol, and as an ingredient in many hand sanitizer products.
Example: Methylated spirits are one form of denatured alcohol.

density – Density is the measurement of the amount of mass per unit volume.
Example: The density of pure water is 1 gram/cm3.

dependent variable – A dependent variable is the variable being tested in a scientific experiment. The dependent variable is ‘dependent’ on the independent variable. As the experimenter changes the independent variable, the change in the dependent variable is observed and recorded.
Example: A scientist is testing the effect of light and dark on the behavior of moths by turning a light on and off. The independent variable is the amount of light and the moth’s reaction is the dependent variable. A change in the independent variable (amount of light) directly causes a change in the dependent variable (moth behavior).

depolymerization – Depolymerization is a process where a polymer is broken into its monomer components.

deposition – Deposition is the settling of particles or sediment onto a surface. The particles may originate from a vapor, solution, suspension, or mixture.

deprotonation – Deprotonation is a chemical reaction where a proton is removed from a molecule by a radical.
Reactions with Bronstead-Lowry bases are deprotonation reactions.
Example: Acetic acid (CH3COOH) is deprotonated by the hydroxide radical (OH) to form the acetate ion (CH3CO2) and water (H2O) by the deprotonation reaction

derived unit – A derived unit is an SI unit of measurement comprised of a combination of the seven base units.
Example: The SI unit of force is the derived unit Newton or N. A Newton is equal to 1 m·kg/s2.

desalination – Desalination is a process to remove salts and minerals from water.

desiccant – A desiccant is a drying agent or a chemical species which picks up water molecules.

desublimation – Desublimation is the phase change directly from gas to solid. Desublimation is the reverse process of sublimation.

detergent – A detergent is a cleaning agent. A detergent is similar to a soap, but with a general structure R-SO4, Na+, where R is a long-chain alkyl group.

detonation – Detonation is an extremely rapid exothermic chemical process where combustion is driven by the energy shock wave produced by the reaction.
Also known as: explosion

Deuteriation – Deuteriation is the process of replacing a hydrogen atom in a molecule with a deuterium atom.
The recommended IUPAC form of deuteriation is deuterio-de-protiation (replacing 1H with 2H).
Example: The deuteriation of fluoroform (CHF3) is CDF3.

deuteride – A deuteride is the anion of the hydrogen isotope deuterium: 2H.

deuterio group – The duterio group is the hydro functional group (-H) where the hydrogen atom is replaced with the hydrogen isotope deuterium. A deuterio group is denoted by -D.

deuterium – Deuterium is one of the heavy isotopes of hydrogen, with one neutron: 2H1.

deuteron – A deuteron is the nucleus of the hydrogen isotope deuterium.

deuteronation – Deuteronation is a chemical reaction that involves the transfer of a deuterium cation or deuteron to a molecule.
Example: The reaction
(CH3)2C=O + [D3O]+ → [(CH3)2C=OD]+ + D2O
is the deuteronation of acetone.

dextrorotatory – Dextrorotatory refers to the property of plane polarized light rotating in a clockwise direction with respect to the light approaching the viewer. Dextrorotatory enantiomers are generally denoted with a D- prefix.

diamagnetic – Diamagnetic is a term which indicates that a substance contains no unpaired electrons and thus is not attracted to a magnetic field.
Example: NH3 is diamagnetic because all of the electrons in NH3 are paired.

diastereomer – Diastereomers are stereoisomers that are not enantiomers or mirror images of each other.

diatomic – Diatomic refers to a molecule containing only two atoms.
Examples: Carbon monoxide (CO) is a diatomic molecule. H2 is a diatomic element.

diazo compound – A diazo compound is an organic compound containing two bonded nitrogen atoms as a terminal functional group. Diazo compounds have the general structure R2C=N+=N.
Example: Diazomethane is the simplest diazo compound.

diazonium compound – A diazonium compound is an organic compound with structure RN=NX where R is an aryl ring and X is any anion.
Also known as: diazonium salt

dichromate – Dichromate is an inorganic polyatomic anion with molecular formula Cr2O72-. Dichromate compounds are good oxidizers.

dichromate compound – A dichromate compound is a compound containing the dichromate anion (Cr2O72-). Dichromate compounds are salts that are weak bases and strong oxidizers.

didymium – Didymium is a mixture of the elements neodymium and praseodymium that was originally thought to be a single element.

diene – A diene is a hydrocarbon that contains two carbon-carbon double bonds.
Example: Isoprene is a diene.

diffraction – Diffraction is the scattering of a wave as it passes an obstruction or gap. The amount of diffraction increases as the wavelength approaches the size of the obstruction or gap.

diffusion – Diffusion is the movement of a fluid from an area of higher concentration to an area of lower concentration. Diffusion is a result of the kinetic properties of particles of matter. The particles will mix until they are evenly distributed.
Example: H2S(g) in a test tube will slowly diffuse into the air of a lab until equilibrium is reached.

dihedral – Dihedral refers to the angle between two bonds in a molecule or angle between two planes defined by three atoms in the molecule. Dihedral angles do not have to apply to atoms that are bonded together. Bond angle is a dihedral angle between two bonds connected to a common atom.

diketone – A diketone is a compound containing two ketone functional groups.
Example: Diacetyl is the simplest diketone molecule.

dilatometer – A dilatometer is a piece of laboratory equipment designed to measure changes in volume caused by chemical reactions or physical processes.

dilute – Dilute refers to a solution containing a relatively small quantity of solute as compared with the amount of solvent. This term is the opposite of ‘concentrated’.

dilution – Dilution is the process of adding a solvent to a solution to lower its concentration.

dimer – A dimer is a polymer made up of two mer subunits bonded together.

diol – A diol is a molecule that contains two hydroxyl groups (-OH).
Also known as: glycol

dioxygenyl – Dioxygenyl is a polyatomic cation with molecular formula O2+. Dioxygenyl ions are formed by the removal of a single electron from O2.

dipolar bond – A dipolar bond is a covalent bond between two atoms where one of the atoms provides both electrons that form the bond.
Also known as: coordination bond, dative bond

dipole – A dipole is a separation of electrical charges. In chemistry, a dipole refers to the separation of charges within a molecule between two covalently bonded atoms.

dipole-dipole interaction – Dipole-dipole interaction is the intermolecular force that occurs when two polar molecules interact with each other. The positively-charged portions of the molecules repel each other and the negatively-charged portions repel each other, while the opposite-charged sections attract each other.
Example: When two sulfur dioxide or SO2 molecules approach, the sulfur atoms repel each other, while the sulfur atoms of one molecule are attracted to the oxygen atom of the other molecule. This interaction affects the orientation of the molecules with respect to each other.

dipole moment – A dipole moment is a measurement of the separation of two oppositely charged charges. Dipole moments are a vector quantity. The magnitude is equal to the charge multiplied by the distance between the charges and the direction is from negative charge to positive charge. Dipole moments are measured in the SI units of coulomb·meters (C m).
In chemistry, dipole moments are applied to the distribution of electrons between two bonded atoms. The existence of a dipole moment is the difference between polar and nonpolar bonds. Molecules with a net dipole moment are polar molecules.

diprotic acid – A diprotic acid is an acid that can donate two protons or hydrogen atom per molecule to an aqueous solution.
Examples: Sulfuric acid (H2SO4) is a diprotic acid.

Dirac’s constant – Dirac’s constant is Planck’s constant divided by 2π. Dirac’s constant is also known as “h bar” or ℏ.
ℏ = 1.054571596×10-34 J·s = 6.58211889×10-16 eV·s

direct proportion – Direct proportion is the relationship between two variables when their ratio is equal to a constant value. As one variable increases, the other variable decreases.
Example: The volume of an ideal gas is directly proportional to the absolute temperature of the gas (Charles’ Law).

disaccharide – A disaccharide is a carbohydrate that is formed when two monosaccharides are joined together and a molecule of water is removed from the structure.
Examples: Lactose is a disaccharide formed from the combination of galactose and glucose. Sucrose is a disaccharide formed from the combination of glucose and fructose.

displacement reaction – A displacement reaction is a type of reaction where part of one reactant is replaced by another reactant. There are also called replacement reactions. Single displacement reactions are reactions where one reactant replaces part of the other.
AB + C → AC + B
Double displacement reactions are reactions where part of one reactant is replaced by part of another reactant.
AB + CD → AD + CB

disproportionation – Disproportionation is a chemical reaction, typically a redox reaction, where a molecule is transformed into two or more dissimilar products. Disproportionation reactions follow the form:
2A → A’ + A”
where A, A’, and A” are all different chemical species.
The reverse reaction of disproportionation is called comproportionation.
Examples: Hydrogen peroxide converting into water and oxygen is a disproportionation reaction.
2 H2O2 → H2O + O2
Water dissociating into H3O+ and OH is an example of a disproportionation reaction that is not a redox reaction.

dissociation reaction – A dissociation reaction is a chemical reaction where a compound breaks apart into two or more parts. The general formula for a dissociation reaction follows the form:
AB → A + B
Example: The reaction H2O → H+ + OH is a dissociation reaction.

dissolve – Dissolve is the process of passing a solute into a solution.

distillate – A distillate is the vapor in a distillation process that is collected and condensed into a liquid.

distillation – Distillation is the technique of heating a liquid to create vapor which is collected when cooled separately from the original liquid.
Example: Pure water can be separated from salt water through distillation. Salt water is boiled to create water steam, but the salt remains in the solution. The steam is collected and allowed to cool into salt-free water.

divalent – Divalent is an ion or molecule with valence of 2.
Also known as: bivalent

divalent anion – A divalent anion is an anion with valence of 2.
Also known as: bivalent anion
Example: The sulfide ion, S2-, is a divalent anion.

divalent cation – A divalent cation is an cation with valence of 2.
Also known as: bivalent cation
Example: A magnesium ion, Mg2+ is a divalent cation.

DNA – DNA is the acronym for deoxyribonucleic acid, usually 2′-deoxy-5′-ribonucleic acid. DNA is a code used within cells to form proteins.

DOT number – The DOT number is a number assigned by the United States Department of Transportation to identify a hazardous or flammable chemical. This number appears on a placard attached to the container along with any hazard ratings.
Also known as NA Number

double bond – A double bond is a bond where two electron pairs are shared between two atoms. Double bonds are drawn as two parallel lines in chemical structure diagrams.
Example: Ethylene (C2H4) is a hydrocarbon with a double bond between the two carbon atoms.

double replacement reaction – A double replacement reaction is a chemical reaction where two reactant ionic compounds exchange ions to form two new product compounds with the same ions. Double replacement reactions take the form:
A+B + C+D → A+D + C+B
Example: The reaction AgNO3 + NaCl → AgCl + NaNO3 is a double replacement reaction. The silver traded its nitrite ion for the sodium’s chloride ion.

drug – A drug is a chemical that has medicinal, performance-enhancing or intoxicating effects when introduced into the body of a human or other animals. Substances which are foods are not considered to be drugs, although active ingredients from foods make be purified for use as drugs. Also, some chemicals used as drugs are identical to substances made in the body (e.g., insulin, testosterone). The chemical is considered a drug only if it is introduced into the body from the outside, such as by ingestion, injection or topical application.

dry cell – A dry cell is an electrolytic cell that uses a slightly moist electrolyte paste as a salt bridge.
Example: Household batteries are dry cells.

dry ice – Dry ice is a common name for carbon dioxide in its solid state.

dubnium – Dubnium is the name for the transition metal element with atomic number 105 and is represented by the symbol Db.

ductile – Ductile is a physical property of a material associated with the ability to be stretched into wire without breaking.

ductility – Ductility is another term for ductile. See definition above.

dynamic equilibrium – A dynamic equilibrium is a chemical equilibrium between a forward reaction and the reverse reaction where the rate of the reactions are equal.

dyne – Dyne is the CGS unit of force. One dyne (dyn) is equal to the force necessary to accelerate a one gram mass by one centimeter per second.

dysprosium – Dysprosium is the name for the lanthanide element with atomic number 66 and is represented by the symbol Dy.