8.2 Lewis Dot Structures

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    Octet Rule

    The octet rule states that most atoms will transfer electrons (ionic bonding) or share electrons (covalent bonding) to obtain a total of 8 electrons in its valence shell.

    ionic bonding
    covalent bonding
    1. A few atoms routinely go under the octet rule
    H only 2
    Be only 4
    B and Al only 6
    2. Third row and lower can exceed the octet rule
    3. Molecules with odd numbers of electrons (ex. NO)

    How to Draw Lewis Structures

    1. Set up skeleton with single bonds (central atom is the atom which can make the most bonds).
    2. Fill the octets of the outside atoms with lone pairs of electrons.
    3. Any remaining valence electrons go on central atom.
    4. Once all electrons are used, form multiple bonds to the central atom if not “full.”

    CH4 Lewis Structure

    CH4 lewis structure

    NH3 Lewis Structure

    NH3 lewis structure

    HCN Lewis Structure

    HCN lewis structure

    Formal Charge

    Formal Charge = Number of Valence e- – [Nonbonding e- + ½ bonding e-]
    Formal Charge = Number of Valence e- – [“dots” + “lines”]


    CO2 Lewis Structure

    CO2 lewis structure

    N2O Lewis Structure

    N2O lewis structure

    SF4 Lewis Structure

    SF4 lewis structure

    NO3- Lewis Structure

    NO3- lewis structure