Understanding Formulae
Chemistry: Cambridge International GCSE Supplement, topic 3.1.1
Understanding Formulae
Atomic theory helped formula writing, making it clearer and consistent. Writing, understanding, and deducing formulae from models and diagrams is key to learning chemical reactions and compounds.
Formulae of elements and compounds
- The formulae for key elements are, for example:
- H2 for Hydrogen; O2 is oxygen.
- Compounds have formulae, for example:
- H2O for water; CO2 for carbon dioxide
- Writing formulae correctly shows the types and numbers of atoms in substances.
Defining molecular formula
- Molecular formula shows the count of each atom type in one molecule.
- For example, glucose has the molecular formula C6H12O6.
- Molecular formula helps describe real molecules beyond simple ratios.
Using models & diagrams for formulae
- To count atoms, you may use models or diagrams:
- If a diagram shows 2 oxygen and 1 carbon atom, the formula is CO2.
- If a model has 1 sodium and 1 chloride atom, it equals NaCl.
- Students usually practice to identify formulae from visual atom arrangements.
- This skill links practical work with formula writing.
Test yourself on Understanding Formulae
What does a molecular formula specifically show?
If a model shows 1 sodium atom and 1 chloride atom, what is the formula of the compound?