Structure 1.4 - Counting particles by mass: The mole

• 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.
• An elementary entity may be an atom, a molecule, an ion, an electron, any other particle, or a specified group of particles.
• Masses of atoms are compared on a scale relative to 12-C and are expressed as relative atomic mass and relative formula mass.
• Relative atomic mass and relative formula mass have no units.
• Molar mass has the units g mol⁻¹.
• The empirical formula of a compound gives the simplest ratio of atoms of each element present in that compound.
• The molecular formula gives the actual number of atoms of each element present in a molecule.
• The molar concentration is determined by the amount of solute and the volume of solution.
• Avogadro's law states that equal volumes of all gases measured under the same conditions of temperature and pressure contain equal numbers of molecules.