Notes on the History of the Atom and Atomic Structure

History of the Atom

• Scientific study is influenced by societal goals and values.
  • Constructs research questions and methodologies based on these goals.

Dalton's Atomic Theory

• Dalton proposed atomic theory to explain Proust's Law of Constant Proportions.
• Key points:
  • Theory vs. Law: A scientific theory explains phenomena, while a law describes what happens without explaining why.
  • Theories are not 'guesses'. They are substantiated explanations based on evidence.
  • A theory does not become a law; they serve different purposes in science.

Structure of the Atom

• Subatomic particles:
  • Protons: Positively charged, identical in all elements, contribute to atomic mass.
  • Neutrons: Neutral particles, discovered by Chadwick, contribute to atomic mass.
  • Electrons: Negatively charged, behave differently under electric fields.
  • Behavior in an electric field:
  • Electrons: Deflected towards anode (greater deflection due to lower mass).
  • Protons: Deflected towards cathode but less than electrons.
  • Neutrons: Not deflected due to lack of charge.

Atomic Mass and Isotopes

• Atomic Mass: Sum of protons and neutrons in an atom.
• Atomic Weight: Weighted average of atomic mass of all natural isotopes of an element.
• Isotopes: Nuclides with the same atomic number but different mass numbers.
  • Example: Carbon-12 ($^{12}C6$) vs. Carbon-14 ($^{14}C6$).