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 N_A = 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:
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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 (A_r): 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 (M_r): Combining individuals A_r 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