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Exploring Early Atomic Theories and Subatomic Particles

Discover the evolution of atomic theory from Democritus to Thomson and the identification of subatomic particles like electrons, protons, and neutrons. Learn about isotopes and the fundamental structure of atoms.

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Exploring Early Atomic Theories and Subatomic Particles

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  1. CHAPTER 4 ATOMIC STRUCTURE

  2. 4.1 Early Theories of Matter • In about 400 B.C., Democritus proposed the earliest recorded atomic theory. He believed that matter was made up of tiny particles, or atoms.

  3. In the 1800’s, John Dalton proposed that “matter can be changed in many ways, but it cannot be created or destroyed”.

  4. 4.2 Subatomic Particles and the Nuclear Atom • In 1897, J.J. Thomson used a cathode ray to study subatomic particles. He discovered the existence of electrons.

  5. Electrons • Have a negative charge. • Are the smallest and fastest subatomic particles • Are located on the outside of the nucleus • The number of electrons are determined by an atom (element’s) atomic number. • Electrons can sometimes be lost or gained

  6. Earnest Rutherford discovered the proton in 1920. • James Chadwick discovered the neutron in 1932.

  7. Protons • Have a positive (+) charge • Are slightly smaller and less dense than a neutron • Are located inside the nucleus • The number of protons are determined by an atom’s (element’s) atomic number. • This number never changes for an element

  8. Neutrons • Have a neutral (0) charge • Are the biggest and heaviest subatomic particle • Are located inside the nucleus • Accounts for most of the atom’s mass • Neutrons are determined by taking the Mass # - Atomic # • This number can vary

  9. In 1910, Robert Millikan was the first scientist to obtain an accurate measurement of an electron’s charge (-1).

  10. Gold-Foil Experiment • The Gold-Foil Experiment was performed in 1909. The experiment launched radiation into a thin strip of gold.

  11. Gold-Foil Experiment • The Gold-Foil Experiment proved that atoms are made of mostly empty space. • Also, most of the mass of the atom is contained in the nucleus.

  12. What is What

  13. Example 1: P E N Symbol • Actinium ___ ___ ___ ____ • Magnesium ___ ___ ___ ____

  14. PP1: P E N Symbol • Carbon ___ ___ ___ _____ • Chlorine ___ ___ ___ _____ • Hydrogen ___ ___ ___ _____ • Yttrium ___ ___ ___ _____

  15. 4.3 How Atoms Differ • Isotopes are atoms that have the same number of protons but a different number of neutrons.

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