1. ATOMS History - Part 1 - Early Theories Democritus and Leucippus = atomos theoryDemocritus and Leucippus = atomos theory Aristotle = 4 basic elements (earth, air, fire, and water)Aristotle = 4 basic elements (earth, air, fire, and water) Alchemists = transmutation of base materials into goldAlchemists = transmutation of base materials into gold

2. Democritus An object cut in half again and again will ultimately reveal a tiny, indivisible particle - the atomosAn object cut in half again and again will ultimately reveal a tiny, indivisible particle - the atomos Couldn’t prove his theory, so everyone believed Aristotle’sCouldn’t prove his theory, so everyone believed Aristotle’s

3. Aristotle

4. The Alchemists

5. Atoms History - Part 2 - John Dalton 18081808 First accepted atomic theoryFirst accepted atomic theory Law Partial Pressures of GasesLaw Partial Pressures of Gases Developed symbols for elements and compounds and table of atomic massesDeveloped symbols for elements and compounds and table of atomic masses

6. Dalton’s Atomic Theory Atoms are tiny, indivisible particlesAtoms are tiny, indivisible particles Atoms of the same element are identical and are different from atoms of a different elementAtoms of the same element are identical and are different from atoms of a different element Atoms of different elements combine in simple, whole number ratios (Law of Definite Proportions)Atoms of different elements combine in simple, whole number ratios (Law of Definite Proportions)

7. ATOMS History - Part 3 - J.J. Thomson “Plum Pudding” model (“chocolate chip” model)“Plum Pudding” model (“chocolate chip” model) 18971897 Mysterious beams of light moved through gas discharge tubeMysterious beams of light moved through gas discharge tube Cathode raysCathode rays

8. Thomson’s Plum Pudding Atom (chocolate chip cookie idea) Positive backgroundPositive background Negative particles randomly spread out through positive backgroundNegative particles randomly spread out through positive background Negative particles = electronsNegative particles = electrons

9. Thomson’s Cathode Ray Tube Experiment The beam moved from the negative side to the positive sideThe beam moved from the negative side to the positive side A magnet’s positive side easily attracted the beamA magnet’s positive side easily attracted the beam A magnet’s negative side easily repelled the beamA magnet’s negative side easily repelled the beam Conclusion: particles are negative and have very little massConclusion: particles are negative and have very little mass

10. Atoms History Part 4 - Ernest Rutherford 19071907 Gold Foil ExperimentGold Foil Experiment

11. Rutherford’s Gold Foil Experiment Shot alpha particles (positively charged) into gold foilShot alpha particles (positively charged) into gold foil Expected alpha particles to go straight through gold atoms (based on Thomson’s atomic model)Expected alpha particles to go straight through gold atoms (based on Thomson’s atomic model) Some went straight through, some were deflected at an angle and some were deflected straight backSome went straight through, some were deflected at an angle and some were deflected straight back

12. Gold Foil Experiment Explained If deflected, alpha particles came close to a positive particle inside the atom (2 positives repel each other)If deflected, alpha particles came close to a positive particle inside the atom (2 positives repel each other) If not deflected, alpha particles passed through a much larger negative areaIf not deflected, alpha particles passed through a much larger negative area

13. Rutherford’s Atom Model Atoms have a very small, massive and dense positive center (NUCLEUS)Atoms have a very small, massive and dense positive center (NUCLEUS) Atoms have a very large, very light mass outer area where the electrons are randomly locatedAtoms have a very large, very light mass outer area where the electrons are randomly located

14. Atoms History Part 4 - Niels Bohr 19131913 Planetary Model to explain electron position outside nucleusPlanetary Model to explain electron position outside nucleus

15. Bohr’s Atomic Model Electrons arranged in orbits outside nucleus, like planets around sunElectrons arranged in orbits outside nucleus, like planets around sun Each electron has a specific orbit with a specific amount of energyEach electron has a specific orbit with a specific amount of energy

16. Atoms History Part 5 Quantum (Modern) Theory There are energy levels and energy levels are subdivided into orbits Electrons can leave their energy level when they absorb energy Electrons return when they give off the energy