1. Evolution of the Atomic Theory: from 400 B.C to late-20 th century Nazli Suyolcu 9D – Hisar Okullari

2. Timeline for the Atomic Theories Democritus- 442 B.C. Lavoisier-1789 Proust-1799 Dalton-1803 Faraday-1832 Stoney-1894 Thomson-1897 Rutherford-1898 Bohr-1922 Milikan-1909 Chadwick-1932

3. Descriptions of the Atomic Theories Democritus (460 B.C.-375 B.C.) Democritus (460 B.C.-375 B.C.)Atomus=indivisible Every matter is composed of constantly moving invisible particles called atoms Indestructible, solid, different for any particular matter Solids -> small pointy Liquids-> large, round

4. Antoine Laurent Lavoisier (1743-1794) “Father of Modern Chemistry” Antoine Laurent Lavoisier (1743-1794) “Father of Modern Chemistry” By evaporating and condensing rain water and weighing the solid residue, he found The Law of Conservation of Masses. Clarified the notion of elements being indivisible even by chemical analysis He added 11 more elements to the Periodic table He developed the first compound nomenclature after their consisting elements which is still in use.

5. Joseph Proust (1754 – 1826) Joseph Proust (1754 – 1826) He experimented with Hydrogen Sulfide by using it as a reagent and noted his observations and data He found the Law of Definite Proportions: every compound is made up of elements in the same particular ratio which built the base of stoichiometry John Dalton (1766-1844) John Dalton (1766-1844) He made additions to Democritus’ theory: Compounds are hard to break into its elements It’s called The Billiard Model Different elements consist of different atoms “Atoms can be neither created nor destroyed.”

6. Michael Faraday (1791-1867) Michael Faraday (1791-1867) Faraday split molecules with electricity what he called “electrolysis” and later Laws of Electrolysis He got the idea that atoms had an electrical parts in them (later on which got called electrons) George J. Stoney (1826- 1911) George J. Stoney (1826- 1911) He introduced the term electron as a subparticle ->Dalton’s theory got disproved

7. J.J.Thomson (1856-1940) He found the so called ‘electron’ by showing the negatively charged particles in cathode rays. He invented the Plum Pudding Model: The atom is positively charged (pudding) It contains electrons in it (plums) This model also explained the atom electroneutrality

8. Ernest Rutherford (1871-1937) He proposed the Nuclear Model by doing his known Gold Foil experiment. The atom has: He proposed the Nuclear Model by doing his known Gold Foil experiment. The atom has: a dens +-charged nucleus (proton) Multiple very-small electrons orbit the nucleus

9. Niels Bohr (1885-1962) Bohr discovered the Planetary Model: The nucleus is surrounded by electrons on orbitals having different energy levels The orbitals have integer numbers (n) The orbitals are circular and have different radii This is the introduction to ‘Quantum’ in chemistry

10. Robert A. Millikan (1868-1953 Robert A. Millikan (1868-1953 Millikan worked on oil droplets and ionized air to observe electrons. He found out that: Electrons had a charge of and integral multiple of 1.59 x 10 -19 C (Planck’s constant) It’s mass is at least 1000 times smaller than the whole atom. James Chadwick 1891-1974 He discovered the neutron(neutral particles) by using the data from Marie Curie’s hydrogen experiment. Neutrons and protons have the same mass

11. In short, the models mentioned throughout the presentation are..

12. Sources TOUPADAKIS, Andreas, Chemistry Reader 2A http://pages.uoregon.edu/ch111/L5.htm http://science.howstuffworks.com/dictionary/famous- scientists/chemists/joseph-louis-proust-info.htm http://science.howstuffworks.com/dictionary/famous- scientists/chemists/joseph-louis-proust-info.htm http://www.livescience.com/32016-niels-bohr-atomic- theory.html http://www.livescience.com/32016-niels-bohr-atomic- theory.html http://www.chalkbored.com/lessons/chemistry-11/atomic- models-handout.pdf http://www.chalkbored.com/lessons/chemistry-11/atomic- models-handout.pdf https://prezi.com/esib9acdwyva/atomic-structure-timeline/