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The amount of heat that must be removed from one gram of a liquid at its freezing point to freeze it with no change in temperature.

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Polymorphous

Refers to substances that crystallize in more than one crystalline arrangement.

Isomorphous

Refers to crystals having the same atomic arrangement.

Stereoisomers

Isomers that differ only in the way that atoms are oriented in space, consist of geometrical and optical isomers.

 

Electron

A subatomic particle having a mass of 0.00054858 amu and a charge of 1-.

Nuclear Reaction

Involves a change in the composition of a nucleus and can evolve or absorb an extraordinarily large amount of energy.

Spectator Ions

Ions in a solution that do not participate in a chemical reaction.

Band of Stability

Band containing nonradioactive nuclides in a plot of number of neutrons versus atomic number.

D -Transition elements (metals)

B Group elements except IIB in the periodic table, sometimes called simply transition elements EX. Fe, Ni, Cu, Ti .
For further information see Metals.

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.

Phase Diagram

Diagram that shows equilibrium temperature-pressure relationships for different phases of a substance.

Net Ionic Equation

Equation that results from canceling spectator ions and eliminating brackets from a total ionic equation.

Metal

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.

Hund's Rule

All orbitals of a given sublevel must be occupied by single electrons before pairing begins.

Exothermicity

The release of heat by a system as a process occurs.

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

Reactants

Substances consumed in a chemical reaction.

Fuel Cells

Voltaic cells in which the reactants (usually gases) are supplied continuously.
A voltaic cell that converts the chemical energy of a fuel and an oxidizing agent directly into electriacl energy on a continuous basis.

Copper

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

Compound

A substance of two or more elements in fixed proportions. Compounds can be decomposed into their constituent elements.

Fat

Solid triester of glycerol and (mostly) saturated fatty acids.