C3: Stochiometry

  1. Element symbols

  • E.g: H is hydrogen

    • Na is sodium

    • K is potassium

  1. Molecular formula of a compound

  • the number and type of atoms in one molecule

  • e.g: H2, H2O, NaCl,..

  1. Chemical formulae and equations

  • Structural formula (simplified): CH3CH2CH2CH3

  • molecular formula: C4H10

  • Formulae of compound ions:

    • Made up of atoms covalently bonded together

    • Have a negative charge (gained electrons to become stable

  • Formulae of compounds:

    • Group I-IV= group number

    • Group V-VII = 8 - group number

    • Group VIII = 0

    • The cross-over method:

  • Molecular formula: number of each type of atom present

  • Formulae of ionic compounds: charges must balance each other

    • Rules:

      • Metals and hydrogen = positively charged

      • Non-metals = negatively charged

      • Transition elements: charge given in brackets

  1. Relative masses of atoms and molecules

  • Relative atomic mass of elements: the average mass of the isotopes of an element compared to 1/12th of the mass of an atom of 12C

  • Molecular mass of compounds

    • Relative molecular mass (Mr): total masses of atoms/ions in the formula

  1. The mole and the Avogadro constant

  • Concentration can be measured in g/dm³

  • The Mole (mol):

    • unit of amount of a substance

    • one mole contains 6.02 × 10²3 particles (atoms, ions, molecules) → avogardo constant

  • Molar mass = mass of one mole of any substance will be equal to the Mr

  • Equation:

  • Molar gas volume: 24 dm³ at room temp

    • mol = V dm³/24 dm³/mol