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Formulae

The chemical formula of a compound shows how many of each type of atom join together to make the units which make up the compound.

For example, in Iron Sulfide every iron atom is joined to one sulfur atom, thus its formula is FeS. In sodium dioxide, there are 2 sodium for every oxygen. Formula being Na₂O. (Numbers are subscript)

there are other more complex formulae. for example:

  • Na₂SO₄ - Sodium sulfate
  • 2 Sodium (Na₂) + 1 sulfur (S) + 4 Oxygen (O₄)

  • Fe(OH)₃ - Ferric oxyhydroxide
  • 1 Iron (Fe) + 3 Hydrogen & Oxygen ((OH)₃) - the brackets make it easier to write

    Chemical Equations

    Word Equations show which chemicals react together (reactants) and what chemicals are produced (products). Symbol Equations allow chemists to work out masses.

    Copper and Oxygen : getting balanced

    reactants: copper, oxygen

    products: copper oxide

    equation: Cu + O₂ -> CuO (this is unbalanced!)

    we need to adjust values to make the left and right sides balanced:

    2Cu + O₂ -> 2CuO

    0            0O
        + O O -> 
    0            0O
    

    (copper is 0, O is oxygen)

    State Symbols

  • s | solid
  • l | liquid
  • g | gas
  • aq | aqueous (dissolved in water)
  • 2Na(s) + 2H₂O(l) -> 2NaOH(aq) + H₂(g)

    2 solid sodium + 2 liquid water -> 2 Sodium Hydroxide (aqueous) + 2 Hydrogen gas

    ^