1.1.4

Empirical & Molecular Formulae

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Empirical and Molecular Formulae

The empirical formula is the simplest formula for a compound. The molecular formula gives the number and types of atoms in a compound.

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Empirical formula

  • The empirical formula is the simplest whole number ratio of the atoms in a molecule.
    • E.g. Ethane has two carbon atoms and six hydrogen atoms.
      • CH3 is the empirical formula for ethane.
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Molecular formula

  • A molecular formula is the actual number of atoms of each element in a molecule. It is always a multiple of the empirical formula.
    • E.g. Ethane has two carbon atoms and six hydrogen atoms.
      • C2H6 is the molecular formula of ethane.
      • This is 2x its empirical formula.
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Experimental determination

  • The empirical formula of a compound is often very easy to determine experimentally.
    • For instance, you could combust a hydrocarbon and find that you get twice as much water vapour as carbon dioxide.
    • This would tell you that its empirical formula is CH4 (remember H2O contains two H atoms).
  • A molecular formula is relatively difficult to determine experimentally.

Jump to other topics

1Physical Chemistry

1.1Atoms, Molecules & Stoichiometry

1.2Atomic Structure

1.3Chemical Bonding

1.4States of Matter

1.5Chemical Energetics

1.6Electrochemistry

1.7Equilibria

1.8Partition Coefficient

1.9Reaction Kinetics

2Inorganic Chemistry

3Organic Chemistry & Analysis

3.1Introduction to Organic Chemistry

3.2Hydrocarbons

3.3Halogen Derivatives

3.4Hydroxy Compounds

3.5Carbonyl Compounds

3.6Carboxylic Acids & Derivatives

3.7Nitrogen Compounds

3.8Polymerisation

3.9Analytical Techniques

3.10Organic Synthesis

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