Chapter 1: History of Chemistry

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Chapter Overview & SLOs

What is the Principle of Conservation of Mass? Established by Antoine Lavoisier, it states that mass cannot be created or destroyed in a closed system. The total mass of reactants always equals the total mass of products. This principle transformed chemistry from a qualitative to a quantitative science focused on accurate measurement.

How do scientific paradigms change? Scientific paradigms are dominant theories that guide research. Paradigms like the Phlogiston theory are replaced when new empirical evidence proves earlier ideas incorrect. Lavoisier's discovery of oxygen's role in combustion demonstrated that metals gained weight during combustion (contrary to phlogiston theory), leading to its replacement.

How did atomic models evolve over time? The atomic model evolved from the Plum-Pudding Model (Thomson) to the Rutherford Model (central nucleus), then to the Bohr Model (quantized orbits), and finally to the Quantum Mechanical Model (uncertainty principle).

These notes are strictly aligned with the Student Learning Outcomes (SLOs) for the FBISE 2026 annual examination.

• How do we explain the Principle of Conservation of Mass? Established by Antoine Lavoisier, it states that mass remains constant during a chemical reaction, which transformed chemistry into a quantitative science focused on accurate measurement.
• How did atomic models evolve over time? The model shifted from the Plum-Pudding Model (electrons in a positive sphere) to the Rutherford Model (central nucleus), then to the Bohr Model (quantized orbits), and finally to the Quantum Mechanical Model incorporating the uncertainty principle.
• How does the periodic table guide research and discovery? By organizing elements by atomic number and recurring properties (periodicity), it allows chemists to predict electronegativity trends and search for superheavy elements like nihonium.
• How is data reliability expressed in chemistry? It is determined by repeatability (consistency by the same researcher) and reproducibility (consistency across different labs), often reported with a 95% confidence level or p-values to show results are not due to random chance.

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