Effective Nuclear Charge

The apparent nuclear charge an electron actually experiences as a result of shielding effects by other electrons.

Elastic Collisions

The transference of energy from one molecule to another as a result of a molecular collision.

Electrolysis

A process in which electrical energy is used to cause a nonspontaneous chemical reaction to occur.

Electrolyte

A substance that, when dissolved in water, results in a solution that can conduct electricity.

Electromagnetic Wave

A wave that has an electric field component and a mutually perpendicular magnetic field component.

Electromotive Force

(emf) - The voltage difference between electrodes.

Electron

A subatomic particle that has a very low mass and carried a single negative electric charge.

Electron Affinity

The negative of the energy change when an electron is accepted by an atom in the gaseous state to form an anion.

Electron Configuration

The distribution of electrons among the various orbitals in an atom or molecule.

Electron Density

The probability that an electron will be found at a particular region in an atomic orbital.

Electronegativity

The ability of an atom to attract electrons toward itself in a chemical bond.

Electrophile

An ion, molecule, or chemical intermediate that seeks a pair of electrons to react with.

Element

A substance that cannot be separated into simpler substances by chemical means.

Elementary Steps

A series of simple reactions that represent the progress of the overall reaction at the molecular level.

Elimination Reactions

Two single bonds from adjacent carbons are broken and replaced with a pi bond. The opposite of an addition reaction.

Emission Spectra

Continuous or line spectra emitted by substances.

Empirical Formula

An expression showing the types of elements present and the ratios of the different kinds of atoms.

Enantiomers

Optical isomers, that is, compounds and their nonsuperimposable mirror images.

End Point

The pH at which the indicator changes color.

Endothermic Processes

Processes that absorb heat from the surroundings.

Energy

The capacity to do work or to produce change.

Enthalpy

A thermodynamic quantity used to describe heat changes taking place at constant pressure.

Enthalpy of Hydration

The heat change associated with the hydration process.

Enthalpy of Reaction

The difference between the enthalpies of the products and the enthalpies of the reactants.

Enthalpy of Solution

The heat generated or absorbed when a certain amount of solute is dissolved in a certain amount of solvent.

Entropy

A direct measure of the randomness or disorder of a system.

Enzyme

A biological catalyst.

Equilibrium

A state in which there are no observable changes as time goes by.

Equilibrium Constant

A number equal to the ratio of the equilibrium concentrations of products to the equilibrium concentrations of reactants, each raised to the power of its stoichiometric coefficient.

Equilibrium Vapor Pressure

The vapor pressure measured under dynamic equilibrium of condensation and evaporation.

Equivalence Point

The point at which the acid has completely reacted with or been neutralized by the base.

Esters

Compounds that have the general formula R’COOR, where R’ can be H or an alkyl group or an aromatic group and R is an alkyl group or an aromatic group.

Ether

An organic compound containing the ROOOR’ linkage, where R and R’ are alkyl and/or aromatic groups.

Evaporation

The process in which a liquid is transformed into a gas; also called vaporization.

Excess Reagents

One or more reactants present in quantities greater than necessary to react with the quantity of the limiting reagent.

Excited State

A state that has higher energy than the ground state.

Exothermic Processes

Processes that give off heat to the surroundings.

Expanded Octet

An atom with more than eight electrons in the valence shell.

Extensive Property

A property that depends on how much matter is being considered.