Overview
This lecture traces the historical development of chemistry from alchemy to modern science, focusing on key figures and foundational laws.
The Birth of Chemistry
- Chemistry evolved from alchemy, moving from mystical ideas to scientific investigation.
- Antoine Lavoisier is credited with founding modern chemistry by establishing coherent theories and systematic experimentation.
- Lavoisier defined elements, named hydrogen and oxygen, and explained combustion.
Lavoisier's Contributions
- Disproved the phlogiston theory by showing combustion requires oxygen.
- Demonstrated that burning and respiration consume oxygen and produce carbon dioxide.
- Formulated the Law of Conservation of Mass: mass is neither created nor destroyed in chemical reactions.
- Careful measurement and quantitative experiments were central to his discoveries.
Later Developments in Chemical Laws
- Joseph Proust established the Law of Definite Proportions: compounds have fixed ratios of elements.
- John Dalton discovered the Law of Multiple Proportions: elements combine in simple whole-number ratios to form different compounds.
- Dalton supported the atomic theory, providing evidence for the existence of atoms.
Molecular Understanding Advances
- Joseph-Louis Gay-Lussac observed that gases combine in simple volume ratios, suggesting atoms have subunits.
- Amadeo Avogadro proposed that equal volumes of gases contain equal numbers of molecules at the same temperature and pressure (Avogadro's Law).
- Avogadro introduced the concept of molecules as groups of atoms, distinguishing them from elements.
Key Terms & Definitions
- Law of Conservation of Mass — Mass is conserved in a chemical reaction; total mass remains unchanged.
- Law of Definite Proportions — A chemical compound always contains the same proportion of elements by mass.
- Law of Multiple Proportions — When elements form more than one compound, the ratios of their masses are simple whole numbers.
- Avogadro's Law — Equal volumes of gases at the same temperature and pressure contain equal numbers of molecules.
- Atom — The smallest unit of an element that retains its properties.
- Molecule — Two or more atoms chemically bonded together.
Action Items / Next Steps
- Review the laws of conservation of mass, definite proportions, multiple proportions, and Avogadro's law.
- Prepare questions for discussion on the transition from alchemy to scientific chemistry.