Lecture Notes: Introduction to Atoms and Elements

Overview

• Transition from measurement focus (Chapter 1) to chemistry.
• Introduction to atoms as the foundation of chemistry.

Section 2.3: The Atom

• Skipping sections 2.1 and 2.2 for now.

Law of Conservation of Mass

• In chemical reactions (chemical change), matter is neither created nor destroyed.
• Example: Sodium (7.7g) reacts with Chlorine (11.9g) to form Sodium Chloride (19.6g).
• Basis for understanding chemical reactions and mass conservation.

Development of Atomic Theory

• Observations led to questioning and theories — Dalton's Atomic Theory.

Dalton's Atomic Theory

1. Elements and Atoms
   • Elements are composed of tiny, indestructible particles called atoms.
2. Identical Atoms
   • All atoms of a given element are identical.
   • Atoms of different elements are different (e.g., Aluminum vs. Iron).
3. Compounds
   • Compounds are composed of atoms of more than one element.
4. Chemical Reactions
   • In chemical reactions, atoms are rearranged but not created or destroyed, explaining mass conservation.

Visual Depictions

• Element A (blue) and Element B (green) with identical atoms.
• Compounds as unions of elements.

Critique of Dalton’s Theory

• Statement 1:
  • Atoms are not indestructible (nuclear chemistry shows atoms can be split).
• Statement 2:
  • Not all atoms of an element are identical due to isotopes.
• Statement 3 & 4:
  • These statements remain true today.

Future Topics

• Isotopes will be discussed later (Chapter 19, Chemistry 107).
• Further exploration of atom indestructibility.

Conclusion

• Dalton’s Atomic Theory as a foundation for modern chemistry.
• Understanding of conservation of mass and atomic structure.