IB Chemistry›Structure 3›3.2›3.2.1
3.2.1

Types of Formulas

Empirical, molecular, structural (full & condensed), and skeletal.

1. Hierarchy of Formulas

Type Definition Example (Butanoic Acid)
Empirical Simplest whole number ratio of atoms. \(C_2H_4O\)
Molecular Actual number of atoms of each element. \(C_4H_8O_2\)
Structural (Full) Shows every bond and every atom (Lewis style). All lines drawn
Structural (Condensed) Shows arrangement without drawing bonds. \(CH_3CH_2CH_2COOH\)
Skeletal Zig-zag lines. Carbons at corners/ends. H on C hidden. Zig-zag ending in OH

2. Skeletal Formulas: The Rules

What to Draw

  • Lines represent bonds.
  • Ends and corners = Carbon atoms.
  • Heteroatoms (O, N, Cl, Br) MUST be drawn.
  • H attached to heteroatoms (e.g., -OH, -NH) MUST be drawn.

What NOT to Draw

  • Do not write 'C' for carbons in the chain.
  • Do not draw H attached to C — they are implied to satisfy carbon's valency of 4.
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