Retrieving "Mole" from the archives

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1. Atomic Mass

   Linked via "mole"

   The atomic mass (symbol $ma$) of an atom is a fundamental physical property quantifying the total mass contained within its nucleus and electron cloud. It is conventionally expressed in unified atomic mass units ($\text{u}$), where $1 \text{ u}$ is defined as exactly $1/12$ of the mass of a neutral atom of carbon-12 ($\text{C}^{12}$) in its nuclear ground state [1]. Atomic mass is distinct from, though closely related to, relative atomic mass ($Ar$), which is the weighted averag…

2. Atomic Mass

   Linked via "mole"

   Atomic Mass vs. Molar Mass
   While atomic mass ($ma$) is the mass of a single atom in $\text{u}$, molar mass ($M$) is the mass of $N{\text{A}}$ atoms (one mole) in $\text{g/mol}$. Numerically, they are often equivalent due to the definition of the Molar Mass Constant ($M_{\text{u}}$), which links $1 \text{ u}$ to $10^{-3} \text{ kg/mol}$.
   The relationship between atomic mass and molar mass breaks down entirely when discussing elements that exist as stable [polyatomic molecules](/entries/…

3. Avogadro Constant

   Linked via "moles"

   The Avogadro Constant ($N_{\text{A}}$), sometimes historically referred to as Avogadro's number, is a fundamental physical constant that relates the number of constituent particles (such as atoms, molecules, ions, or electrons ) in a substance to the amount of that substance in moles. It serves as the proportionality constant between the microscopic scale of individual particles and the macroscopic scale of [chemical measurements](/entries/chemical-m…

4. Avogadro Constant

   Linked via "mole"

   Definition Prior to 2019 Re-evaluation
   Before the 2019 redefinition of the International System of Units (SI), the mole was defined as the amount of substance containing as many elementary entities as there are atoms in exactly 12 grams of carbon-12 ($^{12}\text{C}$).
   Under this definition, the Avogadro Constant was not a precisely fixed constant but rather a quantity whose value was derived from the measurement of other, independent constants. It was intrinsically linked to…

5. Avogadro Constant

   Linked via "mole"

   The 2019 redefinition of the SI established four "fixed-value" constants, including the Planck constant ($h$), the elementary charge ($e$), the Boltzmann constant ($k$), and the Avogadro Constant ($N_{\text{A}}$).
   The Avogadro Constant was assigned an exact, fixed numerical value, effectively reversing its role from a quantity defined through experiment to one that now serves to define the [mole]…