"The definite mass ratios involved in reactions suggested a convenient method for counting the number of atoms of each element participating in the reaction. These results, summarized as the laws of chemical combination,provided overwhelming, if indirect, evidence for the existence of atoms and molecules."

“The conservation of matter in a chemical change is represented in a balanced chemical equation for that process. The study of the relationships between the numbers of reactant and product mole­cules is called stoichiometry. Stoichiometry is fundamental to all as­pects of chemistry.”

“Knowledge of the components of the atom and of the forces that hold them together stimulated entirely new fields of basic science and technology that continue to the present.”

“The science of chemistry rests on two well-established principles: the conservation of matter and the conservation of energy.”

“Quantum mechanics explains the physical stability of the atom by predicting its allowed discrete energy levels and defining the wave functions associated with each energy level. The orbitals determine the probability density for finding the electrons at particular locations in the atom when the electrons are in a specific quantum state.”

“Investigating chemical reactions can be greatly complicated and often obscured by the presence of extraneous materials. So, the first step, therefore, is to learn how to analyze and classify materials to ensure that you are working with pure substances before initiating any reactions.”

“Chemists think in the highly visual nanoscopic world of atoms and molecules, but they work in the tangible world of macroscopic laboratory apparatus. These two approaches to the chemical sciences cannot be divorced.”