Empirical & Molecular Formulae
2 guided lessons · 18 checks · 1. Principles of Chemistry → Chemical Formulae, Equations, Calculations
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Empirical Formulae
Two formulae describe the same compound at two levels of detail: the molecular formula counts every atom, while the empirical formula compresses that count to its simplest whole-number ratio. Organic molecules often differ between the two, and ionic compounds are always written in empirical form.
What you know already
Masses have already been turned into formulae at the bench; this note does the same job on paper from raw numbers. Two names matter: the empirical formula, the simplest whole-number ratio, and the molecular formula, the true atom count in a molecule. The same six-step table then stretches to cover salts with water locked in their crystals.
Key points of understanding
- The molecular formula gives how many atoms of each type sit in one molecule.
- The empirical formula is the simplest whole-number ratio of the atoms of each element present.
- Ethanoic acid shows the gap: molecular C2H4O2 against empirical CH2O.
- Ionic compounds are always written as empirical formulae; organic molecules often differ between the two forms.
- Empirical working is methodical: element, value, relative atomic mass, moles, then ratio.
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1.Empirical Formulae
Two formulae describe the same compound at two levels of detail: the molecular formula counts every atom, while the empirical formula compresses that count to its simplest whole-number ratio. Organic molecules often differ between the two, and ionic compounds are always written in empirical form.
Key points
- The molecular formula gives how many atoms of each type sit in one molecule.
- The empirical formula is the simplest whole-number ratio of the atoms of each element present.
- Ethanoic acid shows the gap: molecular C2H4O2 against empirical CH2O.
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