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- 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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