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History of the Atomic Theory

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Presentation on theme: "History of the Atomic Theory"— Presentation transcript:

1 History of the Atomic Theory

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3 Democritus - Matter Around 500 BCE
Said everything is made up of matter He called these matter, atomos (not cut) This is where the word atom comes from

4 Aristotle - Matter Contrasted Democritus
Said everything is made up of 4 elements Earth Fire Water Wind Most believed Aristotle over Democritus for over 2000 years!

5 John Dalton - Atom In 1803, proposed the first atomic theory
Each element are made up of tiny particles called atoms that are solid spheres Atoms are indivisible and cannot be created nor destroyed All atoms of each element are identical All atoms of one element are different from all atoms of another element Atoms may combine to form compounds Law of multiple proportions We call this the “Billiard Ball” model

6 J.J. Thomson - Electron 100 years after Dalton in 1904
His work around a cathode ray tubes Lead to the idea of negatively charged particles which he called electrons Thomson said that atoms must be neutral so the rest of the solid sphere must be positive Called the plum-pudding model

7 Earnest Rutherford – Nucleus and Proton
1911, he did an experiment of bombarding a gold foil with alpha particles Most alpha particles went through the foil Some deflected slightly Some deflected a lot and some even bounced back He postulated that the atom must have a dense center which is small, he called it the nucleus He also said the center must be positively charged in which he called protons

8 Niels Bohr – Electron Orbital Model
Around 1913, observed different lines of light produced by excited hydrogen gas Said that the lines are produced by different electrons in different orbital levels and that each level can only hold a certain amount of electrons

9 Similarities between Rutherford and Bohr
As Bohr was a student of Rutherford and Bohr did his research in Rutherford’s lab, their models are very similar Typically, their models are blended into one and referred to as the Rutherford-Bohr Model.

10 Homework Page 142 #4 Page 144 #7 and 9


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