| 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.