What is a Lewis dot structure?

A Lewis dot structure (also called an electron dot diagram) is a representation of a molecule showing the valence electrons of each atom as dots, and covalent bonds as lines between atoms. It helps predict molecular shape and bonding.

How do you count valence electrons?

Valence electrons equal the group number for main-group elements. Group 1 = 1 electron, Group 2 = 2, Group 13-17 = 3-7, Group 18 = 8. For a molecule, sum the valence electrons of all atoms and adjust for any ionic charge.

What is the octet rule?

The octet rule states that atoms tend to form bonds until they have 8 electrons in their valence shell (like noble gases). Hydrogen is an exception — it needs only 2 electrons (duet rule). Some elements like sulfur and phosphorus can expand beyond 8.

What is a lone pair in chemistry?

Lone pairs (also called non-bonding pairs) are pairs of valence electrons that are not shared between atoms. They occupy space around the central atom and affect molecular geometry according to VSEPR theory.

Lewis Dot Structure Calculator

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Sources & Methodology

Lewis dot structures follow the octet rule (8 electrons per atom, 2 for hydrogen). Total valence electrons = sum of each atom's group valence electrons. Bonding electrons = 2 × number of bonds. Lone pairs fill remaining electrons on each atom to complete octets.

How to Draw Lewis Dot Structures

Lewis dot structures are a fundamental tool in general chemistry that show how valence electrons are distributed in a molecule. The process follows a systematic set of steps.

Step-by-Step Process

Step 1 — Count total valence electrons: Sum the valence electrons for all atoms. Subtract 1 electron for each positive charge; add 1 for each negative charge.
Step 2 — Identify the central atom: Usually the least electronegative atom (not hydrogen). Carbon and sulfur are common central atoms.
Step 3 — Place single bonds: Connect all surrounding atoms to the central atom with single bonds (2 electrons each).
Step 4 — Complete octets on outer atoms: Add lone pairs to surrounding atoms until each has 8 electrons (2 for H).
Step 5 — Complete the central atom: Place remaining electrons on the central atom as lone pairs.
Step 6 — Form multiple bonds if needed: If the central atom lacks an octet, convert lone pairs on adjacent atoms into double or triple bonds.

Valence Electron Reference

Common atoms: H=1, C=4, N=5, O=6, F=7, Cl=7, S=6, P=5, Si=4, Br=7

Frequently Asked Questions

A Lewis dot structure shows the valence electrons of atoms in a molecule as dots, and covalent bonds as lines. It helps predict bonding, molecular shape, and formal charges. Developed by Gilbert N. Lewis in 1916.

Valence electrons equal the group number for main-group elements: Group 1=1, Group 2=2, Groups 13–17=3–7, Group 18=8. For a molecule, sum the valence electrons of all atoms and adjust for any ionic charge (subtract for cation, add for anion).

The octet rule states atoms tend to form bonds until they have 8 electrons in their valence shell. Hydrogen only needs 2 (duet rule). Some elements like sulfur and phosphorus can have expanded octets (more than 8 electrons) using d-orbitals.

Formal charge = valence electrons − lone pair electrons − (½ × bonding electrons). The best Lewis structure minimizes formal charges (closest to zero) and places negative formal charges on the most electronegative atoms.

Lone pairs (non-bonding pairs) are valence electrons not shared between atoms. They occupy space around the central atom and affect molecular geometry per VSEPR theory. Water (H₂O) has 2 lone pairs on oxygen, giving it a bent shape.

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