Amount of substance GapFill

The relative atomic mass of an element is the weighted mean mass of an atom of the element, considering all its stable isotopes, relative to   the mass of a hydrogen atom1/12 of the mass of a carbon-12 atom1/16 of the mass of a oxygen-16 atom1/14 of the mass of a nitrogen-14 atom. For a molecule, the relative atomic masses of the constituent elements can be added together to give the relative molecular mass; for extended solids, the equivalent is the relative   macromolecularformulacrystalunit mass.

The amount of substance is measured in   moleskilogramspascalsgrams. One of these contains 6.02 × 10²³ (a value known as   Hess'sAvogadro'sPlanck'sLe Chatelier's number) particles, be they atoms, molecules, electrons or formula units. For a gas, if the pressure, temperature and volume of the container are known, the amount of substance can be estimated using the   modelabsoluteclassicalideal gas equation.

Chemical compounds can be represented by two types of formula: one that gives the simplest whole-number ratio of the number of atoms of each element is the   structuralempiricalskeletalmolecular formula, while one that gives the actual number of atoms of each element is the  molecularskeletalstructuralempirical formula.

In a chemical reaction, the relative amounts of each reactant and product, as represented by the coefficients in the reaction equation, is called the  molaritycardinalitystoichiometryordinality. Once understood, it can be used to calculate many useful quantities, including the actual amount of product produced as a percentage of the theoretical maximum (percentage   reactionyieldreturnconversion), and how much of the reactants are incorporated into the desired starting material (atom  wasteefficiencyeconomyproductivity). It is also important in an experimental technique used to determine the concentration of unknown solutions, called   distillationrecrystallisationchromatographytitration.