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Outermost electrons of atoms, usually those involved in bonding.

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Intermolecular Forces

Forces between individual particles (atoms, molecules, ions) of a substance.

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

Law of Definite Proportions (Law of Constant Composition)

The law stating that a pure substance will always have the same percent by weight. Different samples of a pure compound always contain the same elements in the same proportions by mass.

Faraday's Law of Electrolysis

One equivalent weight of a substance is produced at each electrode during the passage of 96,487 coulombs of charge through an electrolytic cell.

Ester

A Compound of the general formula R-C-O-R1 where R and R1 may be the same or different, and may be either aliphatic or aromatic.

Fractional Precipitation

Removal of some ions from solution by precipitation while leaving other ions with similar properties in solution.

Voltaic Cells

Electrochemical cells in which spontaneous chemical reactions produce electricity, also called galvanic cells.

 

Solution

Homogeneous mixture of two or more substances.

Differential Thermometer

A thermometer used for accurate measurement of very small changes in temperature.

Thermonuclear Energy

The energy stored in the nucleus of an atom and released through fission, fusion, or radioactivity. In these processes a small amount of mass is converted to energy according to the relationship E = mc2, where E is energy, m is mass, and c is the speed of light.