44 a schematic representation of the metallic bond in

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Unformatted text preview: -phase degradation mec which a material combines with oxygen to oxide. oxidation (anodic) reaction An electroc reaction that results in the production of e oxygen concentration cell An electroch resulting from oxygen concentration gradi electrolyte. pg036 [V] G2 7-27060 / IRWIN / Schaffer Part I Fundamentals Isolated Mg 2 valence electrons Can be viewed as +12 +2 +2 +2 +2 +2 +2 +2 +2 +2 +2 +2 ion core Ion cores +2 Delocalized cloud of valence electrons +2 +2 +2 Many Mg atoms combine to form a solid metal FIGURE 2.4–4 A schematic representation of the metallic bond in solid Mg. The valence electrons form an electron cloud that surrounds the ion cores. ....................................................................................................................................... EXAMPLE 2.4–4 Predict the most likely type of primary bond in each of these materials: (a) Cu, b KCl, c Si, and d CdTe. Solution To predict primary bond type, one must know the electronegativity values and number of valence electrons for each of the elements involved. From Appendix B, EN(Cu) 1.90, EN(K) 0.82, EN(Cl) 3.16, EN(Si) 1.90, EN(Cd) 1.69, and EN(Te) 2.1. Cu and K have one valence electron, Cd has two, Si has four, Te has six, and Cl has seven valence electrons. a. Since Cu bonds with itself, EN 0 and the bond is not ionic. Cu has an EN value that is neither highly electronegative nor highly electropositive, so we must consider the number of valence electrons. Since Cu has fewer than three valence electrons, it will have metallic bonds. b. For KCl, EN 3.16 0.82 2.34. Using the table in Appendix A, this corresponds to a bond that is 75% ionic. Therefore, we predict the bonding in KCl can be considered chiefly ionic. c. Si (with EN 0) is not ionic. Like Cu, EN(Si) is neither highly electropositive nor highly electronegative. Since Si has four valence electrons, it is likely to display covalent bonds. | v v 36 pgm 1-14-98 plm 3-21-98 MP | e-Text Main Menu | Textbook Table of Contents (b) When the ions at...
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