A Brief History of the Atom - Part 1

A Brief History of the Atom - Part 1

• Democritus proposed the "Atomos" theory, suggesting all matter is composed of indivisible particles
• He created the Solid Sphere Model of the atom (400 BC)
• Antoine Lavoisier developed the Law of Conservation of Mass, stating mass of reactants equals mass of products formed
• This is crucial for balancing chemical equations and calculating theoretical yields
• John Dalton's Atomic Theory combined existing concepts with new research
  • Atoms are indivisible and indestructible (later proven false)
  • Atoms of the same element are identical (later proven false due to isotopes and ions)
  • Atoms of different elements are different
  • Atoms combine in simple whole number ratios to form compounds
  • Dalton introduced the Law of Conservation of Mass and Law of Definite Proportions.
  • Law of Definite Proportions states every compound has fixed proportions of elements by mass (example is Percent Composition)

Further Atomic Model Development

• J.J. Thomson used the Cathode Ray Tube to discover the electron, which was originally called a corpuscle
• He developed the "Plum Pudding" model, depicting a sphere of positive charge with negatively charged electrons embedded within
• Ernest Rutherford's Gold Foil experiment revealed a dense, positively charged nucleus at the atom's center
• This contradicted the Plum Pudding model by showing the atom has a tiny, dense, positive core.
• Rutherford also discovered the proton

Chadwick's Contribution

• James Chadwick discovered the neutron, another subatomic particle within the nucleus.
• This discovery further refined the understanding of the atom's structure.
• Chadwick's finding was part of a follow-up to Rutherford's experiments on the nucleus.