| Formula Type | Shows | Ethanol Example |
|---|---|---|
| Empirical | Simplest whole-number ratio | C₂H₆O |
| Molecular | Actual number of each atom | C₂H₆O |
| Full structural | Every bond drawn explicitly | H-C-C-O-H (with all H) |
| Condensed | Groups written sequentially | CH₃CH₂OH |
| Skeletal | C-C backbone as zig-zag; H on C omitted | Line with -OH at end |
⚠️ Examiner Trap
In a full structural formula, every single bond must be drawn, including those within functional groups. Writing "-OH" instead of "-O-H" will lose the mark. If the question says "structural formula," draw all bonds.
⚠️ Hidden Hydrogens in Skeletal Formulas
When interpreting skeletal structures, remember carbon always has 4 bonds. Count the drawn bonds at each vertex/end and add implicit H atoms to reach 4. Forgetting this leads to wrong molecular formulas.
⚠️ Functional Group Connectivity
Draw -COOH connected through the carbon atom, not through the H. Writing the carboxylic acid group backwards (HOOC-) or connecting through the wrong atom loses marks. The same applies to alcohols: write C-O-H, never C-HO.
Get flashcards and quizzes in ChemEasy, or plan your revision with ChemPlan IB.