In this section, we explore the concept that atoms and molecules are foundational to matter. Initially thought to be indivisible, the advent of experiments in the late 19th century uncovered sub-atomic particles within the atom. Notably, J.J. Thomson's discovery of the electron in 1900 marked a significant shift in atomic theory, demonstrating that atoms comprised smaller units. Alongside this, E. Goldstein's identification of the proton provided insight into atomic structure, leading to the understanding that protons and electrons balance each other's charges within an atom. This knowledge paved the way for more complex atomic models, suggesting that matter at the atomic level is a dynamic interplay of charged particles rather than solid entities.