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The number (6.022x10^23) of atoms, molecules or particles found in exactly 1 mole of substance.

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A two-armed barometer.

First Law of Thermodynamics

The total amount of energy in the universe is constant (also known as the Law of Conservation of Energy) energy is neither created nor destroyed in ordinary chemical reactions and physical changes.

Cloud Chamber

A device for observing the paths of speeding particiles as vapor molecules condense on them to form foglike tracks.

Shielding Effect

Electrons in filled sets of s , p orbitals between the nucleus and outer shell electrons shield the outer shell electrons somewhat from the effect of protons in the nucleus, also called screening effect.


An impure form of carbon obtained by destructive distillation of coal or petroleum.

Oxidizing Agent

The substance that oxidizes another substance and is reduced.

Acid Anhydride

Compound produced by dehydration of a carbonic acid. General formula is R--C--O--C--R. Chemical compound that reacts with water to form an acid and are usually oxides of nonmetallic elements.


Any of three oily, colorless, water-insoluble, flammable, toxic, isomeric liquids, C8H10, of the benzene series, obtained mostly from coal tar: used chiefly in the manufacture of dyes.

Open Sextet

Refers to species that have only six electrons in the highest energy level of the central element (many Lewis acids).

Heat of Fusion

The amount of heat required to melt one gram of solid at its melting point with no change in temperature. Usually expressed in J/g. The molar heat of fusion is the amount of heat required to melt one mole of a solid at its melting point with no change in temperature and is usually expressed in kJ/mol.