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Avogadro’s law
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Amedeo Avogadro
What is Avogadro's law?
How to use the ideal gas law
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Stanislao Cannizzaro
Amedeo Avogadro
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ideal gas law
gas laws
Avogadro’s number
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Amedeo Avogadro
Amedeo Avogadro The Italian mathematical physicist Amedeo Avogadro showed that, under controlled conditions of temperature and pressure, equal volumes of gases contain an equal number of molecules.

Avogadro’s law

chemistry
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Avogadro’s law, a statement that under the same conditions of temperature and pressure, equal volumes of different gases contain an equal number of molecules. This empirical relation can be derived from the kinetic theory of gases under the assumption of a perfect (ideal) gas. The law is approximately valid for real gases at sufficiently low pressures and high temperatures.

What is Avogadro's law?
What is Avogadro's law?How do you weigh a molecule?
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The specific number of molecules in one gram-mole of a substance, defined as the molecular weight in grams, is 6.02214076 × 1023, a quantity called Avogadro’s number, or the Avogadro constant. For example, the molecular weight of oxygen is 32.00, so that one gram-mole of oxygen has a mass of 32.00 grams and contains 6.02214076 × 1023 molecules.

The volume occupied by one gram-mole of gas is about 22.4 litres (0.791 cubic foot) at standard temperature and pressure (0 °C, 1 atmosphere) and is the same for all gases, according to Avogadro’s law.

Diagram showing four types of crystal bonding: ionic bonding with sodium and chlorine ions, covalent bonding with carbon atoms sharing electrons, metallic bonding with iron ions surrounded by free electrons, and molecular bonding with hydrogen molecules held by weak electrical attraction.
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chemical bonding: Avogadro’s law

The law was first proposed in 1811 by Amedeo Avogadro, a professor of higher physics at the University of Turin for many years, but it was not generally accepted until after 1858, when an Italian chemist, Stanislao Cannizzaro, constructed a logical system of chemistry based on it.

The Editors of Encyclopaedia BritannicaThis article was most recently revised and updated by Meg Matthias.