Learn how electrons are shared and transferred between atoms — the language chemists use to draw molecules.
A Lewis dot structure (also called an electron dot diagram) is a simple drawing that shows how the valence electrons — the outermost electrons — of an atom are arranged around it, and how atoms share or transfer those electrons to form chemical bonds.
They were invented by chemist Gilbert N. Lewis in 1916 and remain the most widely used tool for predicting molecular shape and reactivity.
Valence electrons are in the outermost shell of an atom. They're the only ones that participate in bonding. The number of valence electrons equals the element's group number (for main-group elements).
Most atoms are most stable when they have 8 electrons in their outermost shell — a full octet. This drives all chemical bonding: atoms bond to complete their octets, either by sharing electrons (covalent bonds) or transferring them (ionic bonds).
When two atoms share electrons, they can share 1, 2, or 3 pairs. More shared pairs = stronger, shorter bond.
We'll use water (H₂O) as our worked example — one of the most important molecules in chemistry. Follow each step in order to see how the Lewis dot structure is built from scratch.