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Bonds resulting from the head-on overlap of atomic orbitals, in which the region of electron sharing is along and (cylindrically) symmetrical to the imaginary line connecting the bonded atoms.

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Nernst Equation

Corrects standard electrode potentials for nonstandard conditions.

Electromotive Series

The relative order of tendencies for elements and their simple ions to act as oxidizing or reducing agents, also called the activity series.

Boiling Point Elevation

The increase in the boiling point of a solvent caused by the dissolution of a nonvolatile solute.

Octane Number

A number that indicates how smoothly a gasoline burns.

Pairing Energy

Energy required to pair two electrons in the same orbital.


A rare trivalent metallic element, found in gadolinite and other minerals. Symbol: Y, at. wt.: 88.905, at. no.: 39, sp. gr.: 4.47. Cf."rare-earth element."

Yttrium has a silver-metallic luster and is relatively stable in air unless finely divided. Turnings of the metal, however, ignite in air if their temperature exceeds 400oC. Yttrium oxide is one of the most important compounds of yttrium and accounts for the largest use. It is widely used in making YVO4 europium, and Y2O3 europium phosphors to give the red color in color television tubes.

Metathesis Reactions

Reactions in which two compounds react to form two new compounds, with no changes in oxidation number. Reactions in which the ions of two compounds exchange partners.



Discovered : known to ancient civilisations
Origin : The name is derived from 'Cuprum', the Latin name for Cyprus.


An element below and to the left of the stepwise division (metalloids) in the upper right corner of the periodic table, about 80% of the known elements are metals.

Integrated Rate Equation

An equation giving the concentration of a reactant remaining after a specified time, has different mathematical form for different orders of reactants.