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Honors Chemistry Section 3.2

Honors Chemistry Section 3.2. The Structure of the Atom. The Think Tube. Demonstrate the Think Tube. Atom . The smallest particle of an element that still retains the properties of that element. Made of two regions Nucleus In center of atom Extremely small Majority of Mass of Atom

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Honors Chemistry Section 3.2

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  1. Honors ChemistrySection 3.2 The Structure of the Atom

  2. The Think Tube • Demonstrate the Think Tube

  3. Atom • The smallest particle of an element that still retains the properties of that element. • Made of two regions • Nucleus • In center of atom • Extremely small • Majority of Mass of Atom • Protons/Neutrons • Electron Cloud • Contains electrons

  4. The Atom

  5. Parts of the Atom Video

  6. Properties of Subatomic Particles

  7. How did we find the electron? • J.J. Thomson – late 1800’s • Use the Cathode Ray Tube

  8. Thomson's Experiment

  9. Thompson's Experiment Video

  10. Thomson's Observations • Cathode Rays move away from a negative charge • Cathode Rays move away from a magnetic field in the same manner as a wire carrying a negative charge • Found the Cathode Rays have mass – could move a paddle wheel in their path • Charge to mass ratio of Cathode Rays the same regardless of • Type of metal used in electrodes • Type of gas used in tube

  11. Thomson's Conculsions • Cathode Rays are negatively charged • Cathode Rays must be a fundamental particle of matter • Calculated the charge to mass ratio of the particles • Particles later named electrons

  12. Robert Millikan

  13. Millikan's Experiment Video

  14. Millikan's Results • Determined the fundamental charge on matter (the electron) • Used Thomson’s charge to mass ratio to determine the mass of an electron • Verified that electrons are negative

  15. Results • Atom is divisible • One of the basic subatomic particles is the negatively charged electron • Atom is electrically neutral, so it must contain positive charges to balance out the electrons • Electrons have an extremely small mass, therefore there must be other massive particles in the atom

  16. Thomson's and Millikan's Model

  17. Radiation Demonstration • Demo the Cloud Chamber

  18. Ernest Rutherford - 1911 • α particles are positively charged and massive • He nucleus

  19. Rutherford's Results

  20. Rutherford's Experiment Video

  21. Rutherford's Conclusions • Nucleus existed at the center of the atom • Small – extremely small • Massive • Densely Packed • Positive • Electrons are in orbit around the nucleus.

  22. Early 1900's Atomic Theory • All nuclei (execpt H) have protons and neutrons • Proton – positive • Charge equal and opposite the electron • Mass about the same as a neutron • 1.673 x 10-27 kg (1836 x the mass of an electron) • Neutron – electrically neutral • 1.675 x 10-27 kg • Atom neutral so # protons = # electrons • The number of protons determines the identity of the element

  23. Forces in the Nucleus • When two protons are extremely close to each other, there is a strong attraction between them. • A similar attraction exists when neutrons are very close to each other or when protons and neutrons are very close together. • The short-range proton-neutron, proton-proton, and neutron-neutron forces that hold the nuclear particles together are referred to as nuclear forces.

  24. Nuclear Forces

  25. The Size of an Atom • The radius of an atom is the distance from the center of the nucleus to the outer portion of its electron cloud. • Because atomic radii are so small, they are expressed using a unit that is more convenient for the sizes of atoms. • This unit is the picometer, pm.

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