John Dalton

John Dalton introduced the atomic theory into chemistry, proposing that all matter is composed of atoms of different weights that combine in simple ratios. This theory provided the first logical explanation for chemical reactions and the law of multiple proportions. His work on partial pressures of gases also laid the foundation for physical chemistry. Dalton's atomic model, though refined by later discoveries, remains the essential starting point for understanding chemical reactions and the composition of matter in every introductory chemistry course worldwide.