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Lesson : Old Dead Guys. Atom : The smallest particle of an element that keeps all the properties of that element. Dalton’s Theory (Postulates) All matter made of tiny particles called atoms All atoms of the same element are the same
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Lesson: Old Dead Guys Atom: The smallest particle of an element that keeps all the properties of that element.
Dalton’s Theory (Postulates) • All matter made of tiny particles called atoms • All atoms of the same element are the same • Atoms can’t be created or destroyed, or divided into smaller parts • Different atoms combine to make compounds • Atoms are rearranged during chemical changes
JJ Thomson • Cathode Ray Tube experiment • Found out the glowing beam in the tube had a negative charge • Discovered electrons
Thomson’s Theory: Electrons are spread out in a large positive mass. Called the Plum Pudding Model
Rutherford’s Gold Foil Experiment • Fired particles at gold foil • Some particles bounced back • Why? Because of the dense central nucleus
This is Thomson’s idea of an atom. Rutherford thought all the particles would pass straight through the atoms. This is what Rutherford found out: There is a dense nucleus in the middle of the atom.
Rutherford’s Model But what stops the electrons from joining the nucleus? Positive and negative attract…
Bohr’s Model • The electrons must be in energy levels, orbiting around the nucleus. Planetary Model • The electrons can change energy levels depending on their energy
Millikan’s Oil Drop Exp. Discovered the mass – to –charge ratio of an electron