Beginner Topic 27 of 1102 Atomic Structure & Periodicity
Avogadro's Number
The number of particles in one mole, 6.022 x 10^23 per mole.
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In-depth explanation of Avogadro's Number
Avogadro's number, symbol NA, is the number of particles in one mole, and its value is exactly 6.02214076 x 10^23 per mole. Since the 2019 redefinition of the SI it is a defined constant with no uncertainty. The number was chosen so that one mole of carbon-12 has a mass of 12 g. Early estimates came from Jean Perrin's 1908 studies of Brownian motion. The number links the atomic mass unit to the gram, since one u multiplied by NA equals one gram per mole. It allows any count of particles to be converted to an amount in moles.
Going deeper: Avogadro's Number
Key ideas: N_A = 6.022 x 10^23 per mol, the conversion between particle count and amount. Number of particles = n x N_A. Mass of one particle = M / N_A, so one water molecule is 18.02 / 6.022e23 = 2.99 x 10^-23 g. In calculations keep units as mol^-1.
Common mistakes and connections: Students treat Avogadro's number as the same thing as the mole, or use it when a molar mass would be simpler. Avogadro's law (equal volumes of gases hold equal numbers of molecules) is a separate idea. The value was found by Perrin and others, and since 2019 it is fixed exactly.
Visualization of Avogadro's Number
A mole holds 6.022e23 particles, far more than the sand grains on Earth or the stars in the visible universe. The interactive lesson shows this as a live animation or chart.
Worked example and use case
2.5 mol of CO2 contains 2.5 x 6.022 x 10^23 = 1.51 x 10^24 molecules.
Frequently asked questions about Avogadro's Number
What is Avogadro's Number?
The number of particles in one mole, 6.022 x 10^23 per mole.
Is Avogadro's Number a beginner, intermediate or advanced topic?
Avogadro's Number is a beginner topic in Atomic Structure & Periodicity. It needs no earlier chemistry lessons and is a good starting point.
What should I learn before Avogadro's Number?
Study these earlier topics in Atomic Structure & Periodicity first: Relative Atomic Mass, Atomic Mass Unit, Mole.
What comes after Avogadro's Number?
The next topics in Atomic Structure & Periodicity are Molar Mass and Mass Spectrometry.
Can I practise Avogadro's Number with quizzes?
Yes. The interactive lesson includes a self-check question on Avogadro's Number, and the Atomic Structure & Periodicity quiz draws on every topic in this area.
Where Avogadro's Number fits in Atomic Structure & Periodicity
Avogadro's Number is topic 27 of 115 in Atomic Structure & Periodicity.