How to Read Structures
Note: This is a learning resource and may simplify some concepts for educational
purposes.
⚠️ Common Mistakes
- Forgetting implied hydrogens on carbon atoms.
- Miscounting carbons in skeletal structures (count every end and bend!).
- Assuming heteroatoms (O, N, Cl) are hidden (they must be drawn).
1. Lewis Structures
Lewis structures show every atom and every bond. They also show lone pair electrons. This is the most detailed way to draw a molecule but can be cluttered for large molecules.
Example:
Ethanol (Lewis)
2. Condensed Formulas
Text-based representations (e.g., CH3CH2OH). Useful for typing but can be hard to visualize 3D shape.
Example:
Ethanol (Condensed)
CH3CH2OH
3. Skeletal Structures
The standard in organic chemistry. Rules:
- Carbon Atoms: Hidden. Every corner or endpoint of a line is a Carbon.
- Hydrogen Atoms: Hidden if attached to Carbon. You assume enough Hydrogens to give Carbon 4 bonds.
- Heteroatoms: Atoms like O, N, Cl must be drawn explicitly (along with their Hydrogens).
- Bonds: Lines represent bonds. Double lines are double bonds.
Example:
Ethanol (Skeletal)
Comparison Summary
- Lewis: Shows all atoms and lone pairs (best for electron counting).
- Condensed: Compact text representation (best for formulas).
- Skeletal: Standard for reactions and mechanisms.
Worked Example: Ethanol
In ethanol (CH3CH2OH), the skeletal structure shows a bent line with two points (carbons). The –OH group is drawn explicitly because oxygen is a heteroatom.
Practice: Draw it Yourself!
Pick a level and a style, then try to draw the molecule on paper before checking the answer!
1. Choose Difficulty
2. Start Practice Mode
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Related Topic
IUPAC
Naming
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Last updated: 2026-01-13