Lewis structures
ScienceDefinition
Lewis structures are diagrams that show the bonding between atoms in a molecule and the lone pairs of electrons that may exist. They help predict molecular geometry, bond order, and reactivity by illustrating how valence electrons are distributed.
How It Works
- Count the total number of valence electrons from all atoms (adjust for charge if it's an ion).
- Identify the central atom (usually the least electronegative element, never hydrogen).
- Place single bonds between the central atom and each surrounding atom, using 2 electrons per bond.
- Distribute remaining electrons as lone pairs on outer atoms to satisfy the octet rule.
- Place any leftover electrons on the central atom as lone pairs.
- If the central atom lacks an octet, convert lone pairs from adjacent atoms into double or triple bonds.
Examples
- Water (H₂O) has two bonding pairs and two lone pairs on the oxygen atom
- Carbon dioxide (CO₂) has two double bonds and no lone pairs on carbon
- Ozone (O₃) requires resonance structures to accurately represent its electron distribution
Key Fact
Most atoms follow the octet rule (8 electrons); hydrogen follows the duet rule (2 electrons).
Study This Concept
Practice Lewis structures with free review games in these units: