Atomic Theory

Origins – Ancient Greece Aristotle – 4 elements (earth, air, fire, water) Everything is infinitely divisible Democritus – There must be a smallest particle atomos – “indivisible”

John Dalton - Came up with the basis for Modern Atomic Theory All matter is made of atoms Atoms are indivisible All atoms of the same element are exactly the same. All atoms of different elements are different Atoms are not created or destroyed in chemical reactions Compounds form when atoms of different elements combine in definite fixed ratios

Law of Conservation (of Matter) Matter cannot be created or destroyed, only altered in form Mass @ beginning = Mass @ end Law of Definite Proportions One element with combine with another in fixed ratios to form a compound Law of Multiple Proportions Some elements can combine in different fixed ratios to form more than one compound

Progression of Atomic Theory JJ Thompson – discovered the existence of the electron (negative particle) Cathode Ray Experiment 1st Modification! **Bent Away from the negative plate** Solid Sphere Plum Pudding Model

Progression of Atomic Theory Ernest B Rutherford Gold Foil Experiment Alpha (α) particles are positive Bombarded gold (Au) foil with α particles What Happened? Most of the particles went straight through Some were deflected

Gold Foil Experiment Conclusions The atom… is MOSTLY EMPTY SPACE!!!!! has a small, dense, POSITIVE nucleus Rutherford's Nuclear Model

Progression of Atomic Theory Niels Bohr – proposed location of electrons Experimenting with Hydrogen (H2) gas Proposed that electrons orbit the nucleus in distinct energy levels/shells Bohr Model

Progression of Atomic Theory Quantum Mechanics Heisenberg Uncertainty Principle It is impossible to know BOTH the location and movement of an electron at the same time Orbitals – areas of energy where electrons are most likely to be found

Progression of Atomic Models John Dalton Solid Sphere JJ Thompson Plum Pudding Model Rutherford Nuclear Atom Bohr Model Energy Levels Quantum Mechanics Electron-Cloud Model