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Unit 3: Chemical Bonding I - Lewis Theory

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    In this unit, we begin with a general method for predicting the structures of simple covalent molecules and polyatomic ions; we will follow up in the next unit by discussing the actual distribution of electrons in covalent bonds. Even though we will find Lewis Theory has problems with predicting experimental results, it is still used by chemists to establish atomic connectivity and represent chemical reaction mechanisms. Lewis Theory will often serve as your intellectual foundation when predicting molecular properties, upon which you will add using the theories in the next unit.

    A chemical bond is an attraction between atoms that allows the formation of chemical substances that contain two or more atoms. The bond is caused by the electrostatic force of attraction between opposite charges, either between electrons and nuclei, or as the result of a dipole attraction. The strength of chemical bonds varies considerably.

    The learning objectives of this unit are:

    Unit Topic Learning Objectives


    Ionic Bonding

    1. Draw Lewis Dot structures for atoms and ions of the representative elements
    2. Define ionic bonding


    Lattice Energy

    1. Define lattice energy and relate it to Coulomb’s Law
    2. Order ionic compounds in terms of their melting point based on Coulomb’s Law


    Bond Energies

    1. Define bond energy
    2. Use bond energies to calculate a reaction enthalpy


    Covalent Bonding

    1. Differentiate between ionic and covalent bonding
    2. Describe bonding in terms of the balance of attractive and repulsive forces, and sketch a potential energy well
    3. Relate bond energy to bond strength and length
    4. Define electronegativity and use it to predict the degree of iconicity in a bond


    Lewis Structures and the Octet Rule

    1. Identify Lewis Structures
    2. Represent the polarity of a bond in a Lewis Structure using the bond dipole moment vector notation and using the δ+ δ- notation.
    3. Define the octet rule


    Lewis Structures

    1. Draw Lewis structures of covalent compounds


    Formal Charge

    1. Draw Lewis structures of complex ions
    2. Assign formal charges to all the atoms in a Lewis structure
    3. Use formal charges to identify a best Lewis Structure



    1. Define resonance
    2. Draw all the resonance structures for a molecule or ion
    3. Use "curvy" arrows to show the redistribution of electron density to form resonance structures
    4. Use the concept of bond order and bond energy to explain molecular properties


    Exceptions to the Octet Rule

    1. Describe the situations when the octet rule does not apply
    2. Give examples and draw Lewis structures of compounds exhibiting incomplete octets
    3. Give examples and draw Lewis structures of compounds exhibiting expanded octets
    4. Give examples and draw Lewis structures of radicals
    5. Explain why radicals are highly reactive

    Unit 3: Chemical Bonding I - Lewis Theory is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by LibreTexts.

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