Chemical reactions occur on an atomic scale. We cannot physically count individual reacting particles. The mole concept is the essential tool that connects the microscopic world of atoms to the macroscopic world of laboratory measurements.
📘 IB Definition. Memorise This Verbatim
The mole (mol) is the SI unit of amount of substance. One mole contains exactly the number of elementary entities given by the Avogadro constant.
\(N_A = 6.02 \times 10^{23} \text{ mol}^{-1}\)
An elementary entity may be an atom, a molecule, an ion, an electron, or any specified group of particles. Depending entirely on the context.
Molar Mass (M)
Molar mass is the mass of exactly one mole of a given substance, in units of g mol⁻¹. It is numerically equivalent to the relative atomic mass (\(A_r\)) for elements, or the relative formula mass (\(M_r\)) for compounds.
The Fundamental Equation
\[ n = \frac{m}{M} \]