8.2 Lewis Dot Structures

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    Octet Rule

    Atoms will typically transfer or share electrons in an attempt to have 8 electrons around them.

    octet rule ionic bonding
    octet rule covalent bonding

    Octet Rule Exceptions

    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 Dot 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 the central atom.
    4 Once all electrons are used, form multiple bonds to central atom if not “full.”

    Formal Charge

    Formal Charge = Number of Valence e- – [Nonbonding e- + ½ bonding e-]

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

    Rules for Best Formal Charges
    1. Fewer formal charges
    2. Lower magnitude (closer to zero)
    3. Negative charge on more electronegative atom


    Resonance – involves the delocalization of electrons

                        – Affects the bond length and strength