chapter 1 : atoms, molecules stoichiometry

• Relative atomic mass

  The weighted mean mass of an atom of an element relative to an atom of carbon-12 having a mass of exactly 12 units
• Molecular mass

  The weighted average of the mass of a molecule relative to an atom of carbon-12 having a mass of exactly 12 units
• Relative isotopic mass

  The mass of an atom of an isotope on a scale relative to an atom of carbon-12 having a mass of exactly 12 units
• Relative formula mass


  The weighted average of the masses of the formula units relative to an atom of carbon-12 having a mass of exactly 12 units
• Amount of substance

  Measured in moles, based upon the standard count of atoms called the Avogadro constant, measures the number of atoms in a substance
• Avogadro constant (NA)

  The number of atoms per mole of substance, NA = 6.02 x 10^23 mol^-1
• Mole

  The amount of any substance containing as many particles as there are carbon atoms in exactly 12g of carbon-12
• Empirical formula

  The simplest whole number ratio of atoms of each element present in a compound
• Molecular formula

  The actual number of atoms of each element present in a compound
• Calculating empirical formula from composition by mass

  Divide the percentage by the atomic mass

  2. Divide this by the smallest number

  3. This gives you the ratio of atoms in the molecule (or empirical formula)
• what is meant by the term concentration? what equation links concentration and number of moles

  concentration is the amount of solute dissolved per dm3 of solution C=n/v
• number of moles formula

  n=m/Mr
• number of moles (volume)


  n = V(dm3)/24
• stoichiometry


  the proportions of reactants and products