Avogadro's number

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Definition
  1. Noun:
    • A fundamental physical constant: Avogadro's number is the number of constituent particles (usually atoms or molecules) contained in one mole of a substance. It is a key constant in chemistry and physics, linking the macroscopic scale to the atomic scale.
    • The numerical value: Its approximate value is 6.022 × 10²³ per mole.
Usage
  • Avogadro's number is used to perform calculations that convert between the mass of a sample and the number of atoms or molecules it contains.
  • It is a fixed constant used in the definition of the mole, the SI base unit for amount of substance.
Examples
  • Noun:
    • One mole of carbon-12 atoms has a mass of exactly 12 grams and contains Avogadro's number of atoms.
    • To find the number of water molecules in 18 grams of water, you multiply by Avogadro's number.
Advanced Usage
  • "The Avogadro constant" (Nₐ): In precise scientific contexts, the term "Avogadro constant" is often preferred. While "Avogadro's number" is the pure numerical value (approximately 6.022 × 10²³), the "Avogadro constant" has units of mol⁻¹ (e.g., 6.022 × 10²³ mol⁻¹).
    • The Avogadro constant is used to define the kilogram in terms of fundamental atomic properties.
Variants and Related Words
  • Mole (n): The SI unit of amount of substance, defined as containing exactly Avogadro's number of elementary entities.
    • One mole of any substance contains the same number of particles.
  • Avogadro constant (n): The physical constant with units (mol⁻¹), representing the number of particles per mole.
Synonyms
  • Avogadro constant: The preferred term in formal metrology and systeme international (SI) definitions.
Related Phrases/Concepts
  • Molar mass: The mass of one mole of a substance, numerically equal to the atomic or molecular weight in grams. Its calculation inherently uses Avogadro's number.
    • The molar mass of oxygen (O₂) is 32 g/mol, meaning 32 grams contains Avogadro's number of O₂ molecules.
  • Stoichiometry: The branch of chemistry that uses the mole concept and Avogadro's number to calculate reactant and product quantities in chemical reactions.
Noun
  1. the number of molecules in a mole of a substance (approximately 602,250,000,000,000,000,000,000)

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