Avogadro's Number
Definition
The number of particles (atoms, molecules, ions) in one mole of a substance: 6.022 × 10²³. Named after Italian scientist Amedeo Avogadro.
Why is Avogadro's Number Important?
Avogadro's Number is an essential chemistry concept used in laboratories, pharmaceutical development, environmental science, and industrial processes. Understanding this concept is critical for accurate chemical calculations, safe laboratory practices, and optimizing reactions.
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What is Avogadro's Number?
Avogadro's number (Nₐ) is exactly 6.02214076 × 10²³ — the number of particles (atoms, molecules, or ions) in one mole of a substance. Named after Italian scientist Amedeo Avogadro (1776–1856), it is one of the most fundamental constants in chemistry.
How Large is 6.022 × 10²³?
| Analogy | Scale |
|---|---|
| A mole of pennies stacked | Would make a plank 4.5 × 10¹⁷ km long (47 light-years) |
| A mole of rice grains | Would cover all of Earth's land mass 2 meters deep |
| A mole of seconds | = 1.91 × 10¹⁶ years (1.4 million × age of universe) |
| A mole of water molecules | = 18 mL (just over 1 tablespoon) |
How Avogadro's Number is Used
- Moles → Particles: N = n × Nₐ (2 mol H₂O = 2 × 6.022×10²³ = 1.204×10²⁴ molecules)
- Particles → Moles: n = N / Nₐ (3.011×10²³ atoms = 0.500 mol)
- Mass → Particles: N = (mass / molar mass) × Nₐ (36 g H₂O = 2 mol = 1.204×10²⁴ molecules)
How Was It Determined?
Jean Perrin determined Avogadro's number experimentally in 1908 (earning the 1926 Nobel Prize) by studying Brownian motion of particles in suspension. Modern methods use X-ray crystallography of silicon single crystals for the most precise measurements.