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A compound that can be imagined to arise from a partent compound by replacement of one atom with another atom or group of atoms. Used extensively in orgainic chemistry to assist in identifying compounds.

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Water Equivalent

The amount of water that would absorb the same amount of heat as the calorimeter per degree temperature increase.

Polarization

The buildup of a product of oxidation or a reduction of an electrode, preventing further reaction.

Periodicity

Regular periodic variations of properties of elements with atomic number (and position in the periodic table).

Charle's Law

At constant pressure the volume occupied by a definite mass of gas is directly proportional to its absolute temperature.

Semipermable Membrane

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

Nuclides

Refers to different atomic forms of all elements in contrast to ?isotopes?, which refer only to different atomic forms of a single element.

Helium

Discovered : by Sir William Ramsay in London, and independently by P.T. Cleve and N.A. Langlet in Uppsala, Sweden in 1895.
Origin : The name is derived from the Greek ‘helios’,sun.
Description :A colourless, odourless gas that is totally unreactive. It is extracted from natural gas wells, some of which contain gas that is 7% helium. It is used in deep sea diving for balloons and, as liquid helium, for low temperature research. The Earth’s atmosphere contains 5 parts per million by volume, totalling 400 million tons, but it is not worth extracting it from this source at present.
Atomic No:2 MAss No:4

ytterbium

A rare metallic element found in gadolinite and forming compounds resembling those of yttrium. Symbol: Yb, at. wt.: 173.04, at. no.: 70, sp. gr.: 6.96. Cf."rare-earth element."

 

Critical Temperature

The temperature above which a gas cannot be liquefied, the temperature above which a substance cannot exhibit distinct gas and liquid phases.

Insoluble Compound

A very slightly soluble compound.