scan0006 - 308 Chapter8 Bonding Basics Video Lesson Ionic...

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Unformatted text preview: 308 Chapter8 Bonding Basics Video Lesson: Ionic Bonds Visualization: Structure of an Ionic Solid (NaCl) .399!“ 33:4! Crystal structure of sodium chloride. In the crystal structure of NaCl, we note that each sodium ion is surrounded by six chloride ions and that each chloride ion is surrounded by six sodium ions. The resulting crystal possesses a regular close-packed pattern of ions (see Chapter 14). Description of Ionic Bonding Sodium chloride is commercially mined or processed from brine (salt water, such as from the oceans or the Great Salt Lake). In the laboratory, we can combine sodium metal and chlorine gas in a violent reaction to make the salt. The reac- tion, illustrated below, involves the transfer of electrons from sodium atoms to Na(s) + %Cl2(g) —> NaCl(5) AH: —410 kl chlorine. If we look at this reaction more closely, we note that one of the atoms (the metal) loses electrons to become a cation. In our reaction, the sodium atom Na- —> [Na]® + e— loses an electron to become the sodium cation (Na+). The other atom (the non- metal) gains electrons to become an anion. Addition of an electron to a chlorine atom forms the chloride anion (Cl’). The charges on the sodium and chloride 'Cl: + e" —> [iélile ions attract each other, causing the ions to associate with each other in an ion pair (Na+Cl_). But it doesn’t stop there. Other sodium cations are also attracted to the nega— tive charge on the chloride. Other chloride anions are attracted to the positively charged sodium. The end result is a collection of alternating sodium and chloride ions arranged in a solid crystalline lattice, a highly ordered, three—dimensional arrangement of atoms, ions, or molecules (explained in detail in Chapter 13). Within a sodium chloride crystal, each of the sodium cations has six neighboring chloride anions, and each of the chloride anions has siX neighboring sodium cations. The forces of attraction combine to provide a neatly packed crystal of alternating sodium and chloride ions, as shown in Figure 8.4. Examples of Ionic Bonding We can illustrate the formation of an ionic compound such as sodium chloride (NaCl) through the use of Lewis dot symbols. As reflected in their positions on the periodic table, sodium is a metal and chlorine is a nonmetal. Sodium has a relatively low ionization energy and loses an electron to achieve the electron configuration of a noble gas. Na- —-> [Na]® + e— 1522522176351 —> 1522522196 Chlorine, which has a very favorable electron affinity, gains an electron to achieve a noble gas electron configuration. . . . . E) '91: + e’ —» [zen] 1522522p63523p5 —> 15225221263523];6 In the formation of NaCl from Na metal and C12 gas, the electron from the sodium atom is added to the valence shell of the chlorine atom. We can represent this process in equation form by showing the movement of the electron from the sodium atom to the chlorine atom with a fishhook-shaped arrow. The result is a sodium cation and a chloride anion that are attracted to each other. The ionic crystal that results has the formula NaCl. Energy must be added to the system to remove the electron from the sodium atom. Energy, however, is released when that electron is added to the chlorine atom, and even more energy is released when the ionic bond forms. The net result from the ...
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