Atom : The smallest particle of an element that keeps all the properties of that element.

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

Atom : The smallest particle of an element that keeps all the properties of that element.