Understanding Formulas in Chemistry

Empirical vs. Molecular Formulas

• Empirical Formula:
  • Represents the simplest whole-number ratio of atoms in a molecule.
  • Example: CH₂
• Molecular Formula:
  • Represents the actual number of each type of atom in a molecule.
  • Example: C₂H₄ or C₆H₁₂ for the empirical formula CH₂.

Structural Isomers

• Molecules can have the same empirical and molecular formulas but differ in structure.
• Structural Formula:
  • Shows how atoms are connected.
  • Example: C₄H₁₀ can have different structural forms.
• Structural Isomers:
  • Molecules with the same molecular formula but different connectivity.
  • Can possess different properties despite having the same number and type of atoms.

Case Study: C₄H₉Br

• Different structural formulas are possible for the molecular formula C₄H₉Br.
• Exercise:
  • Attempt to draw various structures connecting 4 carbon atoms, 9 hydrogen atoms, and 1 bromine atom.
• Example Solutions:
  • Three possible structural formulas provided.
  • All structures have the same molecular formula but differ in atomic connectivity.

Conclusion

• Hierarchy of Formulas:
  1. Empirical Formula: Ratio of atoms.
  2. Molecular Formula: Exact number of atoms.
  3. Structural Formula: Exact connectivity of atoms.
• Understanding this hierarchy is crucial for determining possible molecular structures from given information.