Lewis Structure Drawer
Draw dot structures, count valence electrons, and check formal charge. This guide explains what the topic is used for, the chemistry ideas behind it, and how students should approach related problems manually.
Valence Electrons, the Fast Way
For main-group elements, the group number is the valence electron count: group 1 has one, group 14 has four, group 17 has seven. Skip the electron configuration and read valence electrons straight off the periodic table position; it is faster and less error-prone than writing out full configurations for every atom in a structure.
Add electrons for negative charge and subtract for positive charge before drawing anything. Getting the total electron count wrong at this stage is the single most common reason a finished structure fails a formal-charge check later.
Exceptions Worth Memorizing
Some atoms break the plain octet rule in predictable ways. Beryllium and boron are stable with fewer than eight electrons around them (BeH2, BF3). Third-row and lower nonmetals such as phosphorus, sulfur, and chlorine can expand past an octet in species like PCl5 and SF6 because they have accessible d-orbitals or hypervalent bonding character.
Odd-electron species such as NO and NO2 cannot satisfy the octet rule for every atom no matter how the electrons are arranged; expect one unpaired electron and do not force a structure that hides it.
Let Formal Charge Choose the Best Structure
When more than one skeleton or electron arrangement is possible, formal charge decides which one is the better representation. Calculate it atom by atom as valence electrons minus nonbonding electrons minus half the bonding electrons, then prefer the structure with the smallest formal charges overall, and place any remaining negative charge on the more electronegative atom.
This tiebreaker is why, for example, the preferred structure of the cyanate ion places negative charge on oxygen rather than carbon, even though other atom arrangements are technically drawable.
What the Interactive Drawer Will Add
The planned tool lets you place atoms, drag bonds and lone pairs, and see a live valence-electron counter that flags when a structure over- or under-fills an atom's shell. It will also auto-calculate formal charge per atom so you can compare candidate structures side by side instead of redoing the arithmetic by hand each time.
Until it ships, work through the shortcuts above with pencil and paper, then use the Molecular Weight Calculator to double-check the formula you are drawing matches the compound you intended.
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Draw dot structures, count valence electrons, and check formal charge. This page explains the underlying chemistry so you can work the problem by hand while the interactive tool is being built.
Not yet. This page is published as a study guide covering the concept, the method, and the common mistakes. The calculators that are already live are linked at the bottom of the page.
The molecular weight calculator, chemical equation balancer, pH calculator, molarity calculator, limiting reagent calculator, percent yield calculator, ideal gas law calculator, half life calculator, dilution calculator, empirical formula calculator, Gibbs free energy calculator, boiling point tools, and the interactive periodic table are all live and free.
Yes. Every page collapses to a single column with mobile-safe inputs and scrollable tables.