E

effective nuclear charge effusion
electrochemical cell electrochemical equivalent
electrode electrode potential
electrolysis electrolyte
electrolytic cell electromagnetic radiation
electromotive force electron
electron affinity electron capture
electron configuration electron dot structure
electronegativity electrophile
electrostatic attraction element
elementary process elimination reaction
empirical formula enantiomer
end point endothermic
energy English system
enthalpy enthalpy of formation
entropy enzyme
equation of state equatorial
equilibrium equilibrium constant
equilibrium constant expression equivalence point
equivalent weight ester
ether exothermic
extensive property  




effective nuclear charge

The amount of positive charge that an electron in an atom experiences, taking into account the shielding effect of other electrons in the atom.


effusion

The escape of a gas through an orifice.


electrochemical cell

A system containing an oxidation-reduction reaction in which oxidation and reduction reactions are physically separated and the transferred electrons pass through an electrical circuit.


electrochemical equivalent

The chemical amount of a substance that reacts in an electrochemical cell as one mole of electrons passes through its circuit.


electrode

In an electrochemical cell, a surface on which oxidation or reduction occurs.


electrode potential

The voltage attributed to one of the half-reactions occurring in an electrochemical cell.


electrolysis

The use of an electrochemical cell to drive a reaction that would otherwise be non-spontaneous.


electrolyte

A substance that dissociates in water to form ions, thus increasing the extent to which the liquid conducts electricity.


electrolytic cell

An electrochemical cell used to drive a reaction that would otherwise be non-spontaneous.


electromagnetic radiation

Energy in the form of oscillating, mutually perpendicular electric and magnetic fields.


electromotive force

The voltage that can develop across an electrochemical cell, used as a measure of the spontaneity of a reaction.


electron

One of the negatively charged, sub-atomic particles (but sometimes behaving as waves) surrounding the nucleus of an atom.


electron affinity

The energy change that occurs as a neutral gaseous atom accepts an electron. Different textbooks define the sign of this quantity differently.


electron capture

A form of radioactive decay in which an electron from an inner shell of an atom is absorbed by the nucleus. In the process a proton is converted into a neutron and the atomic number of the element decreases by one.


electron configuration

A representation of the number of electrons of an atom or ion and the orbitals in which they lie.


electron dot structure

A representation of the bonding in a covalent bond that indicates how many electrons are involved in bonding and how many are unshared on each atom; also called Lewis structure.


electronegativity

The tendency of an atom within a molecule to attract electrons.


electrophile

A species that in its reactions seeks negative charge; acids are typically electrophiles.


electrostatic attraction

The attraction between ions of opposite charge responsible for holding together ionic compounds.


element

A substance containing only one kind of atom and that therefore cannot be broken down into component substances.


elementary process

In a reaction mechanism, one of the steps that can be interpreted in terms of molecular collisions.


elimination reaction

A reaction in which atoms leave a substance to produce a small molecule.


empirical formula

The chemical formula of a substance written using the smallest possible integral subscripts that reflect the elemental composition.


enantiomer

Enantiomers (optical isomers) are molecules whose structures are not superimposable. The structures are mirror images of one another and the molecules are optically active.


end point

The point in a titration at which the indicator changes color.


endothermic

Describing a process that absorbs heat from the surroundings.


energy

The capacity to do work.


English system

A system of units including the inch and the pound.


enthalpy

A thermodynamic state function, symbol H, that equals internal energy plus pressure x volume; the change in enthalpy corresponds to the heat transfer when a reaction occurs at constant pressure.


enthalpy of formation

The enthalpy change that occurs during the formation of a compound from its component elements in their most stable forms.


entropy

A thermodynamic state function, symbol S, that equals the reversible heat transferred divided by temperature; higher entropy corresponds to greater disorder on the molecular scale.


enzyme

A biochemical catalyst made up primarily of protein.


equation of state

An equation giving the relationship among the pressure, volume, temperature, and amount of a substance; most often applied to gases.


equatorial

Oriented about an equator; in a trigonal bipyramidal structure, lying in the trigonal plane.


equilibrium

A state in which no net change is occurring, but which is characterized by forward and reverse reactions occurring at the same rate.


equilibrium constant

The value of the equilibrium constant expression for a system at equilibrium; a value greater than one indicates the position of equilibrium lies toward products, and a value less than one indicates the position of equilibrium lies toward reactants.


equilibrium constant expression

The ratio of the concentrations of products in a reaction raised to the powers of their coefficients divided by the same for reactants; at equilibrium this ratio has the value of the equilibrium constant.


equivalence point

The point in a titration at which the amount of the reactant being added stoichiometrically matches the amount of the reactant initially present.


equivalent weight

The molar mass of a substance divided by the number of moles of that substance that occur in a chemical equation; often used to refer to acids in which case the molar mass is divided by the number of available hydrogen ions.


ester

An organic compound formally derived from a carboxylic acid by the reaction with an alcohol to form the functional group -C(=O)O-R.


ether

An organic compound containing the functional group R-O-R'.


exothermic

Describing a process that releases heat to the surroundings.


extensive property

A property for which the value depends on the amount of matter under consideration.



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