2. Objective 1: Describe the evidence for the existence of electrons, protons, and neutrons, and describe the properties of these subatomic particles. Define atom: smallest particle of an element that retains the chemical properties of that element. Subatomic particles: Protons Neutrons Electrons
3. Discovery of the Electron Late 1800’s – J.J. Thomson discovered the electron through experiments with cathode-ray tubes. Electron Properties Relative Charge Mass Number actual mass - 1 0 9.109 x 10-31 kg Plum Pudding Model of atom
4. Discovery of Atomic Nucleus In 1911 – Ernest Rutherford – Gold Foil Experiment Showed that there was a small – dense positively charged nucleus of an atom. Proton Properties Relative Charge Mass Number actual mass + 1 1 1.673 x 10-27 kg
5. Neutrons Discovered in 1932 by James Chadwick British Scientist Neutron Properties Relative Charge Mass Number actual mass 0 1 1.675 x 10-27 kg
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7. Nucleus compared to rest of atom - approximately size of marble compared to a large football stadium.