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Elements with properties intermediate between metals and nonmetals: B, Al, Si, Ge, As, Sb, Te, Po, and At.

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Semipermable Membrane

A thin partition between two solutions through which certain molecules can pass but others cannot.

Primary Standard

A substance of a known high degree of purity that undergoes one invariable reaction with the other reactant of interest.

Conjugated Double Bonds

Double bonds that are separated from each other by one single bond -C=C-C=C-.

Free Energy Change

The indicator of spontaneity of a process at constnt T and P. If delta-G is negative, the process is spontaneous.

Equilibrium or Chemical Equilibrium

A state of dynamic balance in which the rates of forward and reverse reactions are equal, the state of a system when neither forward or reverse reaction is thermodynamically favored.

Alkali Metals

Metals of Group IA (Na, K, Rb).

Covalent Compounds

Compounds containing predominantly covalent bonds.

Cathode Ray Tube

Closed glass tube containing a gas under low pressure, with electrodes near the ends and a luminescent screen at the end near the positive electrode, produces cathode rays when high voltage is applied.

Combination Reaction

Reaction in which two substances (elements or compounds) combine to form one compound.

Alkyl Group

A group of atoms derived from an alkane by the removal of one hydrogen atom.