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1.5: Bonding

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    75271
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    Before we dive into the whole Schrodinger equation thing let's look at some other areas where quantum mechanics can give use insight into chemistry. Solving the Schrodinger equation is hard, and it better be able to do more than just tell us the electron configurations of the elements!

    Lewis structures

    [Historical note: My presentation of G. N. Lewis' bonding theory does not cling tightly to the historical record. I have added ideas that came from others (notably I. Langmuir), and I have quashed all of Lewis' major blunders. The result is "Lewis theory" as modern chemists recognize it, but it isn't history.]

    Lewis' theory consists of the ideas in the following list. You can jump directly to a detailed essay by clicking on the appropriate title,

    • Valence electrons
      Atoms contain two kinds of electrons, core and valence. Valence electrons, by definition, are the only ones affected by chemical bonding and chemical reactions.
    • Inert gas electron configurations (Lewis octets)
      Inert gas atoms are chemically unreactive because their valence electrons are configured in a way that is unresponsive to other atoms. This electron pattern is called a Lewis octet. Other atoms exchange electrons and form bonds because this reconfigures their valence electrons into inert gas-like patterns, in other words, into Lewis octets.
    • Ions and ionic bonds
      Some atoms create Lewis octets by transferring electrons to or from other atoms. If an atom gains an electron, it becomes a negatively charged anion. If it loses an electron, it becomes a positively charged cation. Oppositely charged ions form compounds that are held together by ionic bonds.
    • Covalent bonds
      Other atoms create Lewis octets by sharing pairs of electrons with other atoms. The shared electron pair is "seen" by both atoms and creates an attractive force between them. This attraction is called acovalent bond.
    • Transfer or share? Energy decides
      Whether an atom transfers or shares electrons is dictated by the change in atom energy. Electrostatic forces make electron transfer most favorable for singly charged ions, like Na+ and Cl-. More highly charged ions are hard to make, and electron sharing becomes a more favorable option.

    Contributor: Alan Shusterman, Reed Organic Chemistry Online

    Since Lewis structures were developed before quantum mechanics there are a lot of "why" questions it leaves unanswered. Why is sharing electrons better than taking them or giving them up? Why eight? Why sometimes less or more than eight?

    Valence bond-hybrid orbital theory

    (WIP) You used it in organic.

    Molecular orbital theory

    (WIP) You used this in organic too a bit.


    1.5: Bonding is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by LibreTexts.

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