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The rates of effusion of gases are inversely proportional to the square roots of their molecular weights or densities.

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Density

Density is the ratio b/w Mass and Volume: D=M/V

Sigma Bonds

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.

Polymerization

The combination of many small molecules to form large molecules.

Central Atom

An atom in a molecule or polyatomic ion that is bonded to more than one other atom.

Catalyst

A substance that speeds up a chemical reaction without being consumed itself in the reaction.
A substance that alters (usually increases) the rate at which a reaction occurs.

xylan

The pentosan occurring in woody tissue that hydrolyzes to xylose: used as a source of furfural.

Basic Anhydride

The oxide of a metal that reacts with water to form a base.

yttrium

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.

Alcohol

Hydrocarbon derivative containing an --OH group attached to a carbon atom not in an aromatic ring. Alcohols are a class of organic compounds containing the hydroxyl group, OH, attached to a carbon atom.

Effective Nuclear Charge

The nuclear charge experienced by the outermost electrons of an atom, the actual nuclear charge minus the effects of shielding due to inner-shell electrons.
Example: Set of dx2-y2 and dz2 orbitals, those d orbitals within a set with lobes directed along the x-, y-, and z-axes.