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Understanding Atomic Theory: Atoms, Molecules, and Ions in Chemistry

This chapter delves into the fundamental concepts of atomic theory including John Dalton's postulates. It explores the nature of elements and atoms, emphasizing that all atoms of an element are identical while differing from others. Key laws such as the Law of Constant Composition, Conservation of Mass, and the Law of Multiple Proportions are discussed. The chapter also highlights significant discoveries by J.J. Thomson, Robert Millikan, and Ernest Rutherford that shaped our modern understanding of atomic structure and the periodic table's role in categorizing elements and their ionic behaviors.

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Understanding Atomic Theory: Atoms, Molecules, and Ions in Chemistry

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  1. AP Chemistry – Chapter 2 Atoms, Molecules and Ions

  2. The Atomic Theory • John Dalton’s Postulates: • Each element is composed of atoms. • All atoms of an element are identical to each other, but different than atoms of other elements. • Atoms of one element cannot be changed into atoms of different elements by chemical reactions; atoms are neither created or destroyed in reactions. • Compounds are formed when atoms of different elements combine.

  3. Laws! • Law of Constant Composition – In a given compound, the relative numbers and kinds of atoms are constant. (CO2 and H2O) • Conservation of Mass – The total mass of products equals the mass of the reactants. Mass is not created or destroyed in a reaction. • Law of Multiple Proportions – If 2 elements combine to form more than one compound, the masses exist in small whole number ratios.

  4. Developing the Current Atomic Theory • J. J. Thomson and the cathode ray tube lead to the discovery of the electron and its charge to mass ratio. • Millikan’s Oil Drop experiment calculated the mass of an electron. • Rutherford’s Gold Foil Experiment determined the atom is mostly empty space with a small dense nucleus at the center of the atom.

  5. Thomson’s Plum Pudding Model

  6. Atomic Structure

  7. Average Atomic Mass The average atomic mass is determined by multiplying the abundance by the mass, and adding these values for all isotopes of that given atom.

  8. The Periodic Table • Metals lose electrons and become positive ions (cations) • Non-metals gain electrons and become negative ions (anions)

  9. The Periodic Table of Elements

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