3.1 Atomic Theory and Atomic Structure

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    Atomic Theory

    1. All matter is composed of atoms.
    2. The atoms of an element are identical but different than atoms of other elements.
    3. The atoms of one element cannot be converted to another element by chemical reactions.
    4. Compounds are formed when atoms of different elements combine in whole number ratios.

    Atomic Structure

    Atomic Structure - An atom is comprised of a nucleus at its center that is composed of protons and neutrons surrounded by an electron cloud.

    Dalton Proposed his atomic theory
    Thompson Discovered electrons
    Millikan Determined the charge of an electron (oil drop experiment)
    Rutherford Discovered the nucleus (scattering of alpha particles in thin gold foil)
    atomic structure

    Isotope Symbols

    Atomic Number – Equals the number of protons
    Mass Number – Equals the sum of the number of protons plus neutrons
    Charge – Equals the number of protons minus the number of electrons
    Isotopes – Forms of elements that have different mass numbers due to differing numbers of neutrons
    isotope symbol

    Atomic Weight (a.k.a. Atomic Mass)

    Isotope Mass Abundance
    35Cl 34.97a.m.u. 75.8%
    37Cl 36.97a.m.u. 24.2%

    What is the atomic mass (also called atomic weight) of chlorine?