A Lewis structure is a diagram that represents the arrangement of atoms and the bonding between them in a molecule. It is named after Gilbert N. Lewis, who introduced the concept in 1916. In a Lewis structure, atoms are represented by their chemical symbol, and the valence electrons (outermost electrons involved in bonding) are represented by dots or lines. The dots are placed around the symbol to indicate the number of valence electrons, and lines are used to represent covalent bonds between atoms. Lewis structures are used to understand the molecular geometry, bonding, and chemical properties of molecules.