Continuation of Chemistry terms, Letters D and E……
D
Dative Bond – A dative bond is a covalent bond between two atoms where one of the atoms provides both electrons that form the bond.
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.
Delocalization – Delocalization is when electrons become free to move all over a molecule, such as when double bonds occur on adjacent atoms in a molecule.
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).
CH3COOH + OH– → CH3CO2– + H2O
Depolymerization – Depolymerization is a process where a polymer is broken into its monomer components.
Desiccant – A desiccant is a drying agent. A chemical species which picks up water molecules
Desublimation – Desublimation is the phase change from gas to solid. Desublimation is the reverse process of sublimation.
Denature – There are two common meanings for this in chemistry. First, it can refer to any process used to make ethanol unfit for consumption (denatured alcohol). Second, denaturing can mean breaking down the three-dimensional structure of a molecule, such as a protein is denatured when exposed to heat.
Detonation – Detonation is a extremely rapid exothermic chemical process where combustion is driven by the energy shock wave produced by the reaction.
Deuteride – A deuteride is the anion of the hydrogen isotope deuterium: 2H–.
Deuterium – Deuterium is one of the heavy isotopes of hydrogen, with one neutron: 12H.
Deuteron – A deuteron is the nucleus of the hydrogen isotope deuterium.
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.
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 particles from an area of higher concentration to one of lower concentration. 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
Dilution – Dilution is when solvent is added to a solution, making it less concentrated.
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.
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.
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
Dissociation reactions are usually reversible chemical reactions. One way to recognize a dissociation is when there is only one reactant, but multiple products.
Displacement Reaction – A displacement reaction is a type of reaction where part of one reactant is replaced by another reactant.
Single displacement reactions are reactions where one reactant replaces part of the other.
Distillation – Distillation is the technique of heating a liquid to create vapor which is collected when cooled separate from the original liquid.
Examples: 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 back into salt-free water.
Dissociation – Dissociation is when a chemical reaction breaks a compound into two or more parts. For example, NaCl dissociates into Na+ and Cl– in water.
Divalent – Divalent is an ion or molecule with valence of 2.
Double displacement reaction – A double displacement or double replacement reaction is when cations of two compounds switch places.
Read Also: Chemistry Terms and Their Meanings {A}
E
Earths – Earths is an alchemical and old chemical term for compounds were thought to be elements but were later discovered to be metal oxides.
Ebullition – a phase transition from the liquid state to the gas state, usually occurring when a liquid is heated to its boiling point. Also Known As: boiling
Example: boiling is seen when water is heated until it forms steam
Eclipsed conformation – Eclipsed conformation is the conformation that occurs when the dihedral angle between two atoms or groups of atoms is 0°. The atoms or groups of atoms around the single bond align with each other where they would overlap or eclipse each other if viewed along the axis of rotation.
Effervescence – Foaming formed as a result of a gas being evolved from a solid or liquid.
Efflorescence – Efflorescence is the process of losing water of hydration from a hydrate.
Effusion – Effusion is the movement of a gas through a pore or capillary into another gaseous region or into a vacuum.
Einstein’s equation – the relation ΔE = Δmc2, relating energy and mass changes, where E is energy, m is mass, and c is the speed of light.
Einsteinium – Einsteinium is the name for the element with atomic number 99 and is represented by the symbol Es. It is a member of the actinide group.
Elastic – A substance is elastic if substance returns to its original shape after being deformed.
Elasticity – Elasticity is a physical property of a material where the material returns to its original shape after being deformed.
Examples: Rubber bands and elastic and other stretchy materials display elasticity.
Elastic limit – Elastic limit is the maximum amount of force that can be applied to a substance before it is no longer elastic.
Elastomer – An elastomer is a polymer that can be stretched and returns to its original shape without permanent deformation. Example: Natural rubber is an elastomer.
Electric circuit – A circuit is a closed path through which electric current can flow. The current can flow in the form of free electrons or as ions. Also Known As: electric circuit, electrical circuit
Electrical conductivity – Electrical conductivity is the measure of the amount of electrical current a material can carry. Electrical conductivity is denoted by the symbol σ and has SI units of siemens per meter (S/m).
Electrical resistivity – Electrical resistivity is the measure of how much a material resists carrying an electrical current. Electrical resistivity is denoted by the symbol ρ and has SI units of ohm meter (Ωm.
Electric dipole – An electric dipole is formed when the centers of positive charges and negative charges do not coincide. Example: Polar molecules are electric dipoles.
Electric field – An electric field is a field around charged particles and changing magnetic fields which exerts a force on charges within the field. Electric field is defined as the electrical force expressed on a stationary positive charge.
Electrochemical Cell – An electrochemical cell is a device that generates a potential difference between electrodes using chemical reactions.
Examples: Galvanic cells and electrolytic cells are examples of electrochemical cells.
Electromotive force – Electromotive force is the electric potential generated by either a electrochemical cell or a changing magnetic field. Electromotive force is commonly denoted by the acronym emf, EMF or a cursive letter E.
The SI unit for electromotive force is the volt.
Electrode – The term is general and can be applied to either the anode or cathode side of an electrical cell.
Electrode potential – Electrode potential is the potential difference between the electrode and its solution.
Electrokinetic potential – The electrokinetic potential is defined as the potential difference across phase boundaries between solids and liquids. In colloids, electrokinetic potential is the electric potential difference across the ionic layer around a charged colloid ion. Typically, the higher the electrokinetic potential, the more stable the colloid. When the zeta-potential equals zero, the colloid will precipitate into a solid. Also Known As: zeta potential
Electrolysis – electrolysis is the passage of a direct electric current through an ion-containing solution. Electrolysis produces chemical changes at the electrodes.
Electrolyte – A substance which forms ions in an aqueous solution.
Examples: NaCl forms Na+ and Cl– in water.
Electrolytic Cell – a type of chemical cell in which the flow of electric energy from an external source causes a redox reaction to occur.
Electromagnetic Radiation – Electromagnetic radiation is self sustaining energy with electric and magnetic field components. Electromagnetic radiation is commonly referred to as ‘light’.
Electron – An electron is a stable negatively charged component of an atom. Electrons exist outside of and surrounding the atom nucleus. Each electron carries one unit of negative charge (1.602 x 10-19 coulomb) and has a very small mass as compared with that of a neutron or proton. Electrons are much less massive than protons or neutrons. The mass of an electron is 9.10938 x 10-31 kg. This is about 1/1836 the mass of a proton.
In solids, electrons are the primary means of conducting current (since protons are larger, typically bound to a nucleus, and thus more difficult to move). In liquids, current carriers are more often ions.
Electron Density – Electron density is a representation of the probability of finding an electron in a specific location around an atom or molecule.
In general, the electron is more likely to be found in regions with high electron density.
Electronegativity – A property of an atom which increases with its tendency to attract the electrons of a bond.
Examples: The chlorine atom has a higher electronegativity than the hydrogen atom, so the bonding electrons will be closer to the Cl than to the H in the HCl molecule.
Electron affinity – Electron affinity reflects the ability of an atom to accept an electron. It is the energy change that occurs when an electron is added to a gaseous atom. Atoms with stronger effective nuclear charge have greater electron affinity.
The reaction that occurs when an atom takes an electron may be represented as:
X + e− → X− + energy
Another way to define electron affinity is as the amount of energy needed to remove an electron from a singly charged negative ion:
X− → X + e−
Electron Capture – Electron capture is a type of radioactive decay where the nucleus of an atom absorbs a K or L shell electron and converts a proton into a neutron. This process reduces the atomic number by 1 and emits gamma radiation and a neutrino.
The decay scheme for electron capture is:
ZXA + e– → ZYA-1 + ν + γ
where
Z is the atomic mass
A is atomic number
X is the parent element
Y is daughter element
e– is an electron
ν is a neutrino
γ is a gamma photon
Electron Cloud – The electron cloud is region of negative charge surrounding an atomic nucleus that is associated with an atomic orbital. The region is defined mathematically, describing a region with a high probability of containing electrons.
Electron Sea Model – The electron sea model is a model of metallic bonding in which cations are considered to be fixed points within a mobile ‘sea’ of electrons.
Electron pair – An electron pair is a pair of electrons in one orbital which have opposite spins or a pair of electrons in a covalent or coordinate bond.
Electron Pair Repulsion – the principle that electron pairs around a central atom tend to orient themselves as far apart as possible. Electron pair repulsion is used to predict the geometry of a molecule or a polyatomic ion.
Electron shell – An electron shell is a set of atomic electrons grouped together by their quantum energy levels.
Electron volt – The electron volt is a unit of energy. One electron volt (eV) is equal to the change in energy as an unbound electron passes through a potential difference of one volt. 1 eV = 1.602176487(40)x10−19 J
Electroplating – Electroplating is a process where a coating of metal is added to a conductor using electricity via a reduction reaction. Electroplating is also known simply as ‘plating’.
When a current is applied to the conductor to be coated, metal ions in solution are reduced onto the electrode to form a thin layer.
Read also: Chemistry Terms and Meanings {B and C}
ELF – ELF is an acronym for Extremely Low Frequency. In general, ELF refers to part of the electromagnetic spectrum with frequencies from 1 to 300 Hz. In radio and atmospheric studies, ELF refers to radio waves with frequencies between 30 and 3000 Hz. Also Known As: extremely low frequency
Elimination reaction – An elimination reaction is a type of chemical reaction where a reactant loses atoms or groups of atoms and forms a double bond.
Embrittlement – Embrittlement is the loss of ductility through a chemical or physical change. Example: Freezing fruit with liquid nitrogen is an example of embrittlement.
Emissivity – Emissivity is the ratio of energy emitted by a material to the energy emitted by a black body at the same temperature. Emissivity values range from 0 to 1. The ‘shinier’ an object is, the lower the emissivity. Dark objects have emissivity values closer to 1.
Emissions – Emissions are the products produced other than heat in a combustion reaction.
Examples: Carbon dioxide is a common emission from combustion reactions
Emission Spectrum – Emission spectrum refers to the range of wavelengths emitted by an atom stimulated by either heat or electric current.
Emission spectra is unique to each element.
Empirical formulae – The empirical formula of a compound is a formula that shows the ratio of elements present in the compound. The ratios are denoted by subscripts next to the element symbols.
Examples: Glucose has a molecular formula of C6H12O6. It contains 2 moles of hydrogen for every mole of carbon and oxygen.
The empirical formula for glucose is CH2O.
Emulsion – An emulsion is a colloid of two or more immiscible liquids where one liquid contains a dispersion of the other liquids.
Examples: Oil and water mixtures are emulsions when shaken together. The oil will form drops and disperse throughout the water
Enantiomer -An enantiomer is one of a pair of optical isomers.
Examples: The central carbon in serine is the chiral carbon. The amino group and hydrogen can rotate about the carbon, resulting in two enantiomers of serine, L-serine and D-serine
Endergonic – Endergonic refers to a chemical reaction where the free energy of the system increases. Endergonic reactions absorb energy from their surroundings and are not spontaneous.
Endothermic – “within heating” from the Greek prefix endo-, meaning “inside” and the Greek suffix –thermic, meaning “to heat”. The term “endothermic” describes a process which absorbs thermal (heat) energy.
Example: Depressuring a pressurized can is an example of an endothermic process.
Energy density – Energy density is the amount of energy stored or available by a system per unit volume.
Engineering – Engineering is the application of scientific principles to design or develop structures, equipment, or processes. The main branches of engineering include electrical engineering, mechanical engineering, chemical engineering, civil engineering, aerospace engineering, automotive engineering, and computer engineering. A person who practices engineering is called an engineer
Enol – An enol is an alkene where a hydroxyl group is attached to one of the double bonded carbonatoms. Example: Butenol is an enol. The hydroxyl group is attached to the third carbon of the alkene chain.
Enolate – An enolate is an anion formed when a hydrogen atom is removed from the hydroxyl group of an enol.
Enriched uranium – Enriched uranium is a sample of uranium where the abundance of the isotope U-235 is increased above the natural abundance. Examples: Nuclear reactors need U-235 to produce a controlled nuclear chain reaction. Natural uranium contains only 0.7% U-235. Nuclear reactor fuel is typically enriched to contain approximately 5% U-235.
Enthalpy – Enthalpy is a thermodynamic property of a system. It is the sum of the internal energy added to the product of the pressure and volume of the system. It reflects the capacity to do non-mechanical work and the capacity to release heat. Enthalpy is denoted as H; specific enthalpy denoted as h. Common units used to express enthalpy are the joule, calorie, or BTU (British Thermal Unit). Enthalpy in a throttling process is constant.
Enthalpy of fusion – Enthalpy of fusion is the change in enthalpy when a solid is melted into a liquid. Also Known As: heat of fusion. Example: The enthalpy of fusion for water is 334 kJ/kg or 79.72 calories/gram.
Enthalpy of reaction – The enthalpy of reaction (ΔHRXN) is the difference between the total enthalpy of the products of a reaction and the total enthalpy of the reactants.
Enthalpy of vaporization – Enthalpy of vaporization is the change in enthalpy when a liquid is converted to a gas at constant pressure. Enthalpy of vaporization is denoted by the symbol ΔHvap. Also Known As: heat of vaporization. Example: The enthalpy of vaporization of water is 2257 kJ/kg.
Enzyme – An enzyme is a protein that functions as a catalyst for a chemical reaction.
Epsom salt – Epsom salt is a common name for the compound magnesium sulfate, MgSO4.
Equation of state – An equation of state is a relation between state variables. It is a thermodynamic equation which describes the state of matter under a given set of physical conditions, typically relating energy, temperature, volume, and pressure. Equations of state most commonly are used to describe the properties of fluids, such as liquids, gases, and plasma, though equations of state may also be applied to solids.
Also Known As: Equations of State, thermodynamic equations
Examples: Examples of equations of state include the Ideal Gas Law, Charles’s Law, Dalton’s Law of Partial Pressure
Equilibrium – Equilibrium is the state of a reversible reaction where the forward reaction rate is equal to the reverse reaction’s rate.
Equilibrium concentration – Equilibrium concentration of a product or reactant is the concentration of an aqueous solution of the reactant or product when the reaction is at chemical equilibrium.
