1.2 The mole concept

  • Particles are classified as either: Atoms, ions, molecules or formula units
  • To perform chemistry, moles of substance are used, and this allows us to make comparisons between chemical species.

The Mole

  • Avogadro’s constant NA = 6.02 x 1023 mol-1
  • Mole: a fixed number of particles and refers to the amount, n, of substance
  • Molar mass: mass of 1 mole of a substance (g mol-1)
  • Number prefixes which are important to know:
  • Prefix Chart

Mole Calculations

Mole Calculations

Relative atomic mass & molar mass

  • Isotopes: Atoms of the same element which have same number of protons
    • Isotopes of an element have different mass numbers
  • Relative abundance: Measure of percentage of isotopes present in element
  • Relative atomic mass (Ar): weighted average of the atomic masses of its isotopes and their relative abundances
    • Relative because compared to 1 atom of carbon-12 (12C) which is 12 units
  • Relative molecular mass (Mr): Combining individuals Ar values of atoms in molecule or formula unit

Empirical and molecular formula determination

  • Empirical formula: simplest whole number ratio of atoms or amount (in mol) of each element present in a compound
  • Molecular Formula: the actual number of atoms or amount (in mol) of elements in one structural unit or one mole of the compound

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