General Chemistry 1 - Chapter 2: Atoms, Molecules, and Ions

Lecture by Iman

Overview

• Chapter Objectives
  1. Fundamental chemical laws
  2. Dalton's atomic theory
  3. Basic structure of an atom
  4. Modern view of atomic structure
  5. Molecules and ions
  6. Introduction to the periodic table
  7. Naming simple compounds

History of Chemistry

• Ancient Greeks: Proposed four fundamental substances (fire, earth, water, air)
• Alchemy: Discovery of elements, mineral acids
• Robert Boyle: Quantitative experiments, relationship between pressure and volume of air
• Antoine Lavoisier: Law of conservation of mass

Fundamental Chemical Laws

1. Law of Conservation of Mass

   • Mass in a closed system remains constant
   • Mass of reactants = Mass of products
   • Example: CH4 + 2O2 -> CO2 + 2H2O

2. Law of Definite Proportions

   • Compounds contain the same proportion of elements by mass

3. Law of Multiple Proportions

   • When two elements form compounds, the ratios of the masses can be reduced to small whole numbers
   • Example: Compounds A, B, C with nitrogen and oxygen

Dalton's Atomic Theory

1. Elements are made of small particles called atoms
2. Atoms of an element are identical; different elements have different atoms
3. Chemical compounds form when atoms combine
4. Chemical reactions involve reorganization of atoms

Structure of an Atom

• Atoms composed of nucleus (protons, neutrons) and electrons
• Electrons determine chemical properties and reactivity
• Historical models:
  • J.J. Thomson: Discovery of electrons (plum pudding model)
  • Ernest Rutherford: Dense nucleus (gold foil experiment)
  • Niels Bohr: Electron orbits (Bohr model)
  • Quantum mechanical model: Electron cloud

Modern View of Atomic Structure

• Subatomic Particles: Protons, neutrons, electrons
• Atomic Number (Z): Number of protons
• Mass Number (A): Total number of protons and neutrons
• Atomic Weight: Weighted average of isotope masses
• Isotopes: Variants with different neutrons
• Atomic Mass Unit (AMU): 1/12th mass of carbon-12
• Moles: Avogadro's number (6.022 x 10^23)
• Molar Mass: Mass of one mole of a substance

Conversion Concepts

• Particles to Moles: Divide by Avogadro's number
• Moles to Mass: Multiply by molar mass
• Mass to Particles: Divide by molar mass, multiply by Avogadro's number

Molecules and Ions

• Ions: Charged particles (cations +, anions -)
• Molecules: Atoms held by covalent bonds
• Ionic Compounds: Opposite charged ions held by ionic bonds
• Bonding Types: Covalent (polar, nonpolar), Ionic
• Electronegativity: Atom's ability to attract electrons

Periodic Table

• History: Mendeleev and Moseley's contribution
• Structure: Periods and groups
• Element Types: Metals, nonmetals, metalloids

Periodic Trends

• Atomic Radius: Decreases left to right, bottom to top
• Effective Nuclear Charge: Increases left to right, bottom to top
• Ionization Energy: Increases left to right, bottom to top
• Electronegativity: Increases left to right, bottom to top
• Electron Affinity: Increases left to right, bottom to top

Naming Compounds

• Binary Ionic Compounds (Type 1): Metal + Nonmetal
• Binary Ionic Compounds (Type 2): Metals with multiple ion charges (use Roman numerals)
• Binary Covalent Compounds (Type 3): Two nonmetals (use prefixes)
• Polyatomic Ions: Memorize common ions
• Acids: Depend on presence of oxygen in the anion

Conclusion

• Next video will cover problem solving related to these concepts
• Importance of understanding basic chemistry laws and naming conventions