ATOM

• Leucippus

  • first proposed the idea of an atom
  • He believed that all things are made up of tiny, indivisible particles
• Democritus

  • a student of Leucippus.
  • He posited that all matter was composed of small indestructible particles, He called Atoms, from the Greek word "atomos", which means "indivisible".
  • Those who supported Leucippus and Democritus's idea of the atom were called atomists.
• Aristotle

  • strongly opposed Leucippus and Democritus theory
  • He believed that all the things can be divided infinitely, therefore, he said there was no smallest part of matter.
  • He also claimed that all matter consisted of four elements: Earth, Fire, Water, and Air.
• John Dalton

  • He revived the idea of atomic theory 2,000 years
  • He formulated his atomic theory based on Antoine Lavoisier's: Law of Conservation of Mass and Joseph Proust's Law of Definite Proportion
• Postulates of Dalton's Atomic Theory

  1. Matter is composed of small indivisible particles called atoms
  2. Atoms of the same element are identical
  3. Compounds contain atoms of more than one element
  4. A chemical reaction involves only the separation, combination, rearrangement of atoms
• Billiard Ball Model

  • Proposed By John Dalton that described the atom as a tiny and indivisible particle
• J.J. Thomson

  • discovered that an atom is composed of negative charged particles which was named electrons using Cathode Ray Tube experiment
• Ernest Rutherford

  • discovered the nucleus and the nucleus is the center of the atom.
  • Verified Thomson's atomic model by conducting his gold foil experiment using radioactive substances that emitted alpha particle rays
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  Neils Bohr

  • He Placed each electron on a specific energy level.
  • Electron moved in definite orbits around the nucleus just like the movement of planets around the Sun in the solar system.
  • Planetary Model
• Eugene Goldstein

  • He discovered the positively charged subatomic particle as a component of anode rays
  • But Rutherford who coined the term proton
• James Chadwick

  • He discovered the neutral particles which he called Neutrons.
  • Neutrons is in the nucleus of an atom
• The Electron Cloud Model (Wave Model)

  • the most recent model of was based on the principle of wave mechanics
  • The modern model of atoms state that an atom is composed of a small positively charge nucleus, surrounded by a large region where there are enough electrons surrounding the nucleus to make an atom neutral