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Many representative elements attain at least a share of eight electrons in their valence shells when they form molecular or ionic compounds, there are some limitations.

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Isomorphous

Refers to crystals having the same atomic arrangement.

Conformations

Structures of a compound that differ by the extent of rotation about a single bond.

Specific Heat

The amount of heat required to raise the temperature of one gram of substance one degree Celsius.

Rate of Reaction

Change in the concentration of a reactant or product per unit time.

Nucleons

Particles comprising the nucleus, protons and neutrons.

Hydrogen

Discovered : by Henry Cavendish in 1766.
Isolated in London, UK.
Origin : The name is derived from the Greek ‘hydro genes’, meaning water forming.
Description :A colourless, odourless gas that burns and can form an explosive mixture with air. It is currently manufactured from methane gas, but is also produced by the electrolysis of water and aqueous salts. The gas is used to make such key materials as ammonia, cyclohexane and methanol, which are intermediates in the production of fertilisers, plastics and pharmaceuticals. Some see hydrogen gas as the clean fuel of the future - generated from water and returning to water when it is oxidised. Hydrogen-powered fuel cells are increasingly being seen as pollution-free sources of energy.

Critical Mass

The minimum mass of a particular fissionable nuclide in a given volume required to sustain a nuclear chain reaction.

Salicylate

A salt or ester of salicylic acid.

Lanthanide Contraction

A decrease in the radii of the elements following the lanthanides compared to what would be expected if there were no f-transition metals.

Varieties of garnet minerals

The most famous type of garnet stone is pyrope (flaming). This is the "oldest of garnets", with a dense red color, similar to the grain of an edible garnet. Pyrope has a variety called rhodolite - a stone of dense pink or pink-purple color, which sometimes has the alexandrite effect and is used in elite jewelry.