What are Lewis Dot Structures?
Lewis dot structures (Lewis structures) are diagrams that show the valence electrons of an atom and how they are shared or transferred between atoms in chemical bonds. They help chemists visualize bonding, predict molecular geometry, and understand reactivity.
A Lewis structure uses dots around an element's symbol to represent valence electrons. Lines or pairs of dots between atoms show covalent bonds; lone pairs appear as pairs of dots around an atom. They show both bonding and non-bonding electrons.
- •One shared pair (2 electrons)
- •Written as C–C or C:C
- •Atoms touching lightly
- •Example: ethane C₂H₆
- •Two shared pairs (4 electrons)
- •Written as C=C or C::C
- •Atoms held closer
- •Example: ethene C₂H₄
Step-by-step worked examples
Draw the Lewis structure of H₂O (water).
Oxygen has 6 valence electrons, each H has 1. Total = 6 + 1 + 1 = 8 electrons (4 pairs). O in center, bonded to 2 H atoms (2 bonding pairs). Oxygen keeps 2 lone pairs. Structure: H–O–H with 2 dots on oxygen.
Draw the Lewis structure of CH₄ (methane).
Carbon has 4 valence electrons, each H has 1. Total = 4 + 4(1) = 8 electrons (4 pairs). C in center bonded to 4 H atoms. All 4 pairs are bonding pairs; no lone pairs on C. Structure: carbon surrounded by 4 hydrogens.
Draw the Lewis structure of N₂ (nitrogen gas).
Each N has 5 valence electrons. Total = 5 + 5 = 10 electrons (5 pairs). N atoms triple bonded (N≡N) = 3 bonding pairs + 2 lone pairs. Structure: N:::N with one lone pair on each N.
Flashcards
Quick quiz
Q1.How many valence electrons does carbon have?
Q2.In the Lewis structure of O₂, how many lone pairs are on each oxygen?
Q3.A triple bond in Lewis notation means…
Q4.What is the octet rule?
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Common mistakes
Thinking valence electrons and total electrons are the same. — Correct: Valence electrons are only those in the outermost shell; Lewis structures show only these, not inner shells.
Drawing more bonds than atoms can support. — Correct: Each atom can only share/bond according to its valence electrons. Hydrogen bonds to 1; carbon to 4; nitrogen to 3–4.
Forgetting to include lone pairs. — Correct: Lone pairs are crucial—they affect molecular shape, polarity, and reactivity. Always show them.
Assuming a line always means a single bond. — Correct: A single line = single bond (2e⁻), double line = double bond (4e⁻), triple line = triple bond (6e⁻).
FAQ
How do I draw a Lewis structure?
Count total valence electrons. Place the least electronegative atom in the center. Arrange other atoms around it. Distribute electrons as bonding pairs (lines) first, then lone pairs.
Can hydrogen have more than one bond?
No. Hydrogen has only 1 valence electron, so it can form only 1 bond (the duet rule).
What if the total valence electrons is odd?
Then the molecule has an unpaired electron (a radical). Examples: NO, NO₂.
Why is the Lewis structure important?
It shows bonding, lone pairs, and electron distribution—all essential for predicting geometry, polarity, reactivity, and properties.