British scientist John Dalton (1766-1844), French scientist Joseph Louis Gay-Lussac (1778-1850), and Italian scientist Amedeo Avogadro (1776-1856) are familiar to many chemistry students. Such students may understand the importance of Dalton's atomic theory, model how Gay-Lussac's law relates the pressure and the temperature of a gas, and use Avogadro's number to correctly convert between the atomic and the macroscopic. However, these historical scientists contributed far more to the development of modern chemistry than most students might realize. To illuminate their contributions, the author designed a lesson grounded in Avogadro's settling of a debate between Gay-Lussac and Dalton on how atoms combine at the simplest level. The story of the discovery of atomic bonding can improve students' basic understanding of chemistry. In the early 19th century, scientists were trying to differentiate between elements (containing a single type of atom) and compounds (more complex substances containing multiple types of atoms). They were also searching for the process by which atoms combine. The debate among Gay-Lussac, Dalton, and Avogadro is essential to this story. During a two-day lesson, the author introduces this historical debate before moving on to atomic structure and bonding. The resulting class discussion addresses the nature of science, promotes productive struggle, develops critical-thinking skills, and aligns with the "Next Generation Science Standards."