Atomic Theory and Atomic Structure

Introduction

• Topic: Atomic theory and atomic structure, part of a high school chemistry series on atoms, molecules, and ions.
• Future lessons: Introduction to the periodic table and nomenclature (naming compounds).
• Release: Weekly lessons throughout the 2020-21 school year.

Atomic Theory

• Pioneered by John Dalton
  • Known as the father of modern atomic theory.
• Four Tenets of Modern Atomic Theory:
  1. All matter is composed of atoms.
  2. All atoms of an element are identical, but different from atoms of other elements.
  3. Atoms cannot be converted into different elements by normal chemical reactions (only by nuclear processes).
  4. Atoms combine in whole-number ratios to form compounds (e.g., water is H₂O).

Important Figures in Atomic Theory

• J.J. Thomson

  • Discovered the electron using a cathode ray tube.
  • Determined the mass-to-charge ratio of the electron.

• Robert Millikan

  • Determined the charge of an electron through the oil drop experiment.
  • This allowed for the calculation of the electron's mass.

• Ernest Rutherford

  • Discovered the nucleus using the gold foil experiment.
  • Concluded that atoms consist mostly of empty space with a dense nucleus.

Structure of the Atom

• Subatomic Particles

  • Protons (p): Positively charged
  • Neutrons (n): No charge; neutral
  • Electrons (e): Negatively charged

• Nucleus

  • Contains protons and neutrons.
  • Most of an atom's mass is concentrated here.

• Electron Cloud

  • Electrons move rapidly around the nucleus.
  • The size of the electron cloud compared to the nucleus is vast (e.g., marble nucleus, half-mile electron cloud).

• Atomic Mass Unit (amu)

  • Used to express the mass of subatomic particles (1 amu for protons and neutrons, 1/1822 amu for electrons).

Isotopes and Atomic Symbols

• Isotope Symbols

  • Example: Oxygen-16 (16/8 O)
  • Atomic number (bottom) = Number of protons
  • Mass number (top) = Total protons and neutrons
  • Charge notation if ions are present

• Isotopes

  • Variants of the same element with different numbers of neutrons (e.g., Oxygen-16, Oxygen-18).

Periodic Table and Atomic Weight

• Periodic Table

  • Atomic number = Number of protons, identifies the element.
  • Atomic mass/weight: Average mass of all isotopes.

• Atomic Weight Calculation

  • Weighted average of isotopes based on natural abundance.
  • Use percentage of abundance and isotopic mass to calculate average.

Conclusion

• Summarizes the lesson on atomic theory and structure.
• Encourages engagement with the lesson series for further study and practice materials.