Chem. Chap. 8 Outline - Chapter 8: Basic Concepts of...

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Chapter 8: Basic Concepts of Chemical Bonding 1. On the table in most diners, you can expect to find the two white crystalline substances shown in the photograph: table salt and granulated sugar. 2. The properties of substance are determined in large part by the chemical bonds that hold their atoms together. 8.1: Chemical Bonds, Lewis Symbols, and the Octet Rule a) Whenever two atoms or ions are strongly attached to each other, we say there is a chemical bond between them. b) The term ionic bond refers to electrostatic forces that exist between ions of opposite charge. c) A covalent bond results from the sharing of electrons between two atoms. d) Metallic bonds are found in metals, such as copper, iron, and aluminum. 2) Lewis Symbols a) The electrons involved in chemical bonding are the valence electrons, which, for most atoms, are those residing in the outermost occupied shell of an atom. b) The Lewis symbol for an element consists of the chemical symbol for the element plus a dot for each valence electron. c) The dots are placed on the four sides of the atomic symbol: the top, the bottom, and the left and right sides. d) The electron configurations and Lewis symbols for the representative elements of the second and third rows of the periodic table are shown in table 8.1. 3) The Octet Rule a) Atoms often gain, lose or share electrons to achieve the same number of electrons as the noble gas closest to them in the periodic table. b) An octet of electrons consists of full s and p subshells in an atom. 8. 2: Ionic Bonding a) When sodium metal, Na (s) , is brought into contact with chlorine gas, Cl 2(g) , a violent reaction ensues. b) The formation of Na + from Na and Cl from Cl 2 indicates that an electron has been lost by a sodium atom and gained by a chlorine atom; we can envision an electron transfer from the Na atom to the Cl atom. c) The arrow indicates the transfer of an electron from the Na atom to the Cl atom. 2) Energetics of Ionic Bond Formation a) As seen in Figure 8.2, the reaction of sodium with chlorine is very exothermic. b) In equation 8.2 we represented the formation of NaCl as the transfer of an electron from Na to Cl. c) The principal reason that ionic compounds are stable in the attraction between ions of unlike charge. d) To get a picture of this process for NaCl, imagine that the structure show in figure 8.3 expands from within, so that the distances between the ions increase until the ions are very far apart. e) Table 8.2 lists the lattice energies of NaCl and other ionic compounds. f) The magnitude of the lattice energy of a solid depends on the charges of the ions, their sizes, and their arrangement in the solid. 3) Electron Configurations of Ions of the Representative Elements a) We began considering the electron configurations of ions in Section 7.4.
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b) Even though lattice energy increases with increasing ionic charge, we never find ionic compounds that containNa +2 ions. c)
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Chem. Chap. 8 Outline - Chapter 8: Basic Concepts of...

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