Chemistry - A Molecular Science

Glossary

Electronegativity (

)χ

is a relative measure of the

ability of an atom to attract bonding electrons to itself. Atoms with high electronegativities have unfilled orbitals that are low in energy.

An

electronic transition

is the changing of the energy

of an electron from one quantum state to another.

An

element

is a pure substance th

at cannot be broken

down into a simpler substance by chemical means.

The

elemental composition

of a compound is a listing

of the relative masses, usually expressed as percents, of the elements in the compound.

An

elementary reaction

is a reaction that occurs in

one step.

Emission

is the ejection of a photon by an atom or a

molecule. The energy of the atom or molecule decreases by the energy of the photon (h

ν).

An

empirical or simplest formula

is a chemical

formula that indicates on

ly the smallest whole

number ratio of the atoms present in the compound.

Enantiomers

are two molecules that are non-

superimposable mirror images of one another.

An

endothermic

process absorbs heat.

The

end point

is the point at which an indicator

changes color. The end point should be nearly the same as the equivalence point.

Energetics

is a combination of thermodynamics and

kinetics.

Energy

is the capacity to do work or to transfer heat.

An

energy band

is a region of allowed energy in a

metal in which there is no separation between adjacent energy levels.

The

energy of interaction

is the energy of two

interacting particles relative to the energy of the

two particles when they are not interacting. Energies of interaction in chemistry result from the electrostatic interactions.

The

enthalpy or heat of combustion

is the heat

absorbed when one mole of

a substance reacts with

oxygen. Heats of combustion are negative because they are exothermic.

The

enthalpy or heat of reaction

is the heat absorbed

by a reaction run at constant temperature and pressure. A negative heat of reaction simply means that the heat is given off not absorbed.

Entropy

is the thermodynamic measure the number of

ways in which a system can distribute its energy. It is often related to the disorder in the system.

An

enzyme

is a biological compound (usually a

protein) that acts as a catalyst.

The

equilibrium constant (K)

is the value of the

reaction quotient (

Q) when equilibrium activities

are used.

The

equivalence point

is the point in a titration at

which stoichiometric amounts of reactants are present.

Esters

are compounds with the general formula

RCOOR’,

i.e.,

two groups connected by a carboxyl

group.

Esterification

is a conde

nsation reaction between a

carboxylic acid and an alco

hol to produce an ester

and water.

Evaporation

is the conversion of a liquid to its vapor.

An

excited state

is an allowed state that is not the

lowest energy state.

An

exothermic

process gives off heat.

Exponential decay

is a decrease in concentration that

goes as e

-x. First order reactions undergo

exponential decay: [A] = [A]

-kTeo

.

An

extensive property

is one that depends upon the

amount of material. Mass and volume are extensive properties. Also see intensive property.

An

extensive reaction

is one with a large equilibrium

constant. If a reaction is extensive, then the equilibrium concentration of least one of the reactants will be very small.

F

A

face centered cubic (

fcc

unit cell is one in which )

the atoms that are located

in the corners are also

found in the centers of the faces.

The

factor label method

is a method that uses the

labels (units) of the factors to determine the order and manner in which the factors should be used to convert one quantity into another.

Family

See group.

The

Faraday (

F

) is the charge of one mole of

electrons. 1

F = 96,485 C/mol.

A

fatty acid

is a carboxylic acid with a long

hydrocarbon chain.

The

Fermi level

the highest occupied energy level in a

band.

A

ferrimagnet

is a magnetic material whose particles

have opposing but unequal spins.

A

ferromagnet

is a magnetic material whose particles

have aligned spins.

Ferromagnetism

is a bulk magnetism in a material

(such as iron) resulting from the alignment of the spins of adjacent atoms in the same direction.

The

first law of thermodynamics

states that energy is

neither created nor dest

royed in any process.

Fission

is the process in which a heavy nucleus splits

into lighter nuclei.

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State

University