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A thermodynamic state or property that measures the degree of disorder or randomness of a system.

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Radioactive Tracer

A small amount of radioisotope replacing a nonradioactive isotope of the element in a compound whose path (for example, in the body) or whose decomposition products are to be monitored by detection of radioctivity, also called a radioactive label.


A substance added to react with the charge, or a product of its reduction, in metallurgy, usually added to lower a melting point.

Inert s-pair Effect

Characteristic of the post-transition minerals, tendency of the outermost s electrons to remain nonionized or un shared in compounds.

Absolute Zero

The zero point on the absolute temperature scale, -273.15°C or 0 K, theoretically, the temperature at which molecular motion ceases. The concept of an absolute zero temperature was first deduced from experiments with gases. When a fixed volume of gas is cooled, its pressure decreases with its temperature. Absolute zero physically possesses quantum mechanical zero-point energy.

Particulate Matter

Fine divided solid particles suspended in polluted air.

Third Law of Thermodynamics

The entropy of a hypothetical pure, perfect, crystalline sustance at absolute zero temperature is zero.


A unit of energy in the SI system. One joule is 1 kg. m2/s2 which is also 0.2390 calorie.

Heat of Solution

The amount of heat absorbed in the formation of solution that contains one mole of solute, the value is positive if heat is absorbed (endothermic) and negative if heat is released (exothermic).

Colligative Properties

Physical properties of solutions that depend upon the number but not the kind of solute particles present.

Valence Bond Theory

Assumes that covalent bonds are formed when atomic orbitals on different atoms overlap and the electrons are shared.

Differential Thermal Analysis (DTA)

A technique for observing the temperature, direction, and magnitude of thermally induced transitions in a material by heating/cooling a sample and comparing its temperature with that of an inert reference material under similar conditions.

Monoprotic Acid

Acid that can form only one hydronium ion per molecule, may be strong or weak. Acid that contains one ionizable hydrogen atom per formula unit.

Outer Orbital Complex

Valence bond designation for a complex in which the metal ion utilizes d orbitals in the outermost (occupied) shell in hybridization.

Oxidation-reduction Reactions

Reactions in which oxidation and reduction occur, also called redox reactions.

Background Radiation

Ratiation extraneous to an experiment. Usually the low-level natural radiation form cosmic rays and trace radioactive substances present in our environment.

Method of Initial Rates

Method of determining the rate-law expression by carrying out a reaction with different initial concentrations and analyzing the resultant changes in initial rates.

Metallic Bonding

Bonding within metals due to the electrical attraction of positively charges metal ions for mobile electrons that belong to the crystal as a whole.

Geometrical Isomers

Compounds with different arrangements of groups on either side of a bond with restricted rotation, such as a double bond or a single bond in a ring, for example cis-trans isomers of certain alkenes. Stereoisomers that are not mirror images of each other, also known as position isomers.

Heterogeneous Catalyst

A catalyst that exists in a different phase (solid, liquid or gas) from the reactants, a contact catalyst.

Forbidden Zone

A relatively large energy separation between an insulator's highest filled electron energy band and the next higher energy vacant band. Beginning in the fourth energy level, a set of seven degenerate orbitals per energy level, higher in energy than s, p, and d orbitals of the same energy level.