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The structure of the atom

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Presentation on theme: "The structure of the atom"— Presentation transcript:

1 The structure of the atom
Chapter 3.2 The structure of the atom

2 Objectives Summarize the observed properties of cathode rays that led to the discovery of the electron. Summarize the experiment carried out by Rutherford and his co-workers that led to the discovery of the nucleus. List the properties of protons, neutrons, and electrons. Define atom.

3 Structure of the Atom Define atom: smallest particle of an element that retains the chemical properties of that element. Nucleus very small region located at the center of an atom Contains Protons – positive charged particle Neutron – particle with NO charge Area surrounding nucleus Electron cloud Electrons – negative charged particle Subatomic particles Visual Concept – Click Here

4 Properties of subatomic particles

5 Discovery of the Electron
Late 1800’s – J.J. Thomson discovered the electron through experiments with cathode- ray tubes. Plum Pudding Model of atom Robert A. Millikan – 1909 – Oil drop experiment Electron is 1/1837 the mass of hydrogen atom Visual Concept 1 – Click Here Visual Concept 2 – Click Here

6 Discovery of the Atomic Nucleus
In 1911 – Ernest Rutherford – Gold Foil Experiment Showed that there was a small – dense positively charged nucleus of an atom. Visual Concept – Click Here

7 Composition of the Atomic Nucleus
All atomic nuclei are made of protons and neutrons. Atoms are electrically neutral - contain equal numbers of protons and electrons Nuclear Forces – Short range proton-neutron, proton-proton, and neutron-neutron forces that hold the nuclear particles together Sizes of Atoms Nucleus compared to rest of atom - approximately size of marble compared to a large football stadium. Atom is mostly empty space

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