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4.6.1: Back to Sodium Chloride

  • Page ID
    52318
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    By this point, we have concluded that NaCl is composed of Na+ ions (cations) and Cl ions (anions), but we have not yet discussed how these ions are arranged with respect to one another in space. As you may have come to expect, there is usually more than one way to represent a chemical structure. Different models emphasize different features of a substance but none of them are real in the sense that if we could look at the molecular-level structure, these models are not what we would see. At the same time, visible cubes of salt crystals provide a clue to atomic-molecular structure. If we follow the structure down from the macroscopic to the molecular, this cubic/rectangular structure is retained. A diagram of sodium chloride showing the relative positions of the ions, shown here, illustrates this cubic organization.

    Another way to look at NaCl is to think of each Na+ ion as being surrounded by six Cl ions, and each Clion is surrounded by six Na+ ions. Such an arrangement is possible because of the relative sizes of the sodium and chloride ions; the smaller Na+ ions can sit in the holes between the larger Cl ions (why are the chloride ions bigger than the sodium ions?). One consequence of this arrangement is that there is not an “ionic” bond that is analogous to a covalent bond. Our model of bonding here is best understood as this three-dimensional lattice of interacting ions. The alternating network of positive and negative ions makes for a very stable structure that is difficult to disrupt. The implication? Lots of energy is required to break these interactions and allow the ions to move with respect to one another. Many ionic compounds are organized in similar kinds of crystalline structures. A complexity (to which we will return in Chapter 6) is that many ionic compounds, including NaCl, are highly soluble in water, which means they interact strongly with water molecules. Often salts crystallize together with water molecules and form hydrated (with water) forms, as opposed to anhydrous (without water) forms.


    4.6.1: Back to Sodium Chloride is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by LibreTexts.

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