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4.4: "Component Within": Introduction and Indicator

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  • Learning Objectives
    • Identify the indicator information associated with "component within" molar relationships.

    As stated previously, chemists established a new unit, the mole, in order to relate a variety of measurements to one another and to chemically-significant quantities.  The previous two sections of this chapter defined and discussed Avogadro's number, which quantifies the number of individual atoms, ions, or molecules that are present within a substance.  Because these particle counts are chemically-significant quantities, Avogadro's number, which has an approximate value of 6.02 × 1023, was identified as a fundamental chemical measurement and, therefore, defined as a molar standard.

    A second fundamental chemical quantity will be discussed in the following paragraphs, and its associated equality pattern will be presented and applied in Section 4.5.

    "Component Within"

    In Chapter 2, compounds, which can also be referred to as molecules, were defined as pure substances that contain two or more elements that are combined in a specific ratio.  The majority of the content within Chapter 3 was dedicated to explaining the derivation of these ratios.  Recall that ionic compounds exist due to the electrostatic attraction between charged particles.  However, a single positively-charged cation or negatively-charged anion cannot exist alone in nature, as its charged state is inherently destabilizing.  Therefore, these particles must associate with one another in specific ratios, in order to form a stable, net-neutral species.  Alternatively, covalent bonds are established when the unpaired electrons in neutral atoms interact with one another to form shared pairs of electrons.  The number of unpaired electrons possessed by each constituent atom determines the relative placement of these particles within the final covalent molecule.  More specifically, the element with more unpaired electrons becomes the central atom in the molecule, and the other element is used as a surrounding atom.  Additionally, one surrounding atom is paired with each of the central atom's unpaired electrons, in order to satisfy the valences of all of the atoms that are involved in the pairing process.  Therefore, the number of unpaired electrons found on the central atom ultimately dictates the relative ratio in which a given combination of elements will bond.

    Due to the defined nature of the processes described above, establishing the number of ions or atoms that must be combined to form ionic compounds or covalent molecules, respectively, is fundamental to the study of chemistry.  As a result, the relative ratios of the component particles found within molecules are chemically-significant quantities and, therefore, are defined as molar standards. 

    "Component Within" Indicator Information

    The phrase "component within" is used to describe the molar quantities that indicate the relative ratios of the elements that are present within a compound or molecule.  Unlike Avogadro's number, which is indicated for use in a problem-solving context by the presence of specific key words, the indicator for "component within" molar relationships is highly generic:  In order to apply a "component within" equality, the given problem must refer to both a complete molecule and one of its constituent elements.

    For example, consider a problem that would require a calculation of how many moles of Ag are present in 11.5 moles of Ag2CO3.  Because both a complete molecule, Ag2CO3, silver carbonate, and a component element found within this molecule, Ag, silver, are referenced in the given problem, a "component within" equality should be developed and applied when solving the problem. 

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