answers - CONCEPT CHECK QUESTIONS AND ANSWERS Chapter 2...

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Unformatted text preview: CONCEPT CHECK QUESTIONS AND ANSWERS Chapter 2 Atomic Structure and Interatomic Bonding Concept Check 2.1 Q u e s t i o n : Why are the atomic weights of the elements generally not integers? Cite two reasons. A n s w e r : T h e a t o m i c w e i g h t s o f t h e e l e m e n t s o r d i n a r i l y a r e n o t i n t e g e r s b e c a u s e : ( 1 ) t h e atomic masses of the atoms normally are not integers (except for 12 C), and (2) the atomic weight is taken as the weighted average of the atomic masses of an atom's naturally occurring isotopes. Concept Check 2.2 Q u e s t i o n : Give electron configurations for the Fe 3+ and S 2- ions. A n s w e r : T h e F e 3+ ion is an iron atom that has lost three electrons. Since the electron configuration of the Fe atom is 1 s 2 2 s 2 2 p 6 3 s 2 3 p 6 3 d 6 4 s 2 (Table 2.2), the configuration for Fe 3+ is 1 s 2 2 s 2 2 p 6 3 s 2 3 p 6 3 d 5 . T h e S 2- ion a sulfur atom that has gained two electrons. Since the electron configuration of the S atom is 1 s 2 2 s 2 2 p 6 3 s 2 3 p 4 (Table 2.2), the configuration for S 2- is 1 s 2 2 s 2 2 p 6 3 s 2 3 p 6 . Concept Check 2.3 Q u e s t i o n : Offer an explanation as to why covalently bonded materials are generally less dense than ionically or metallically bonded ones. A n s w e r : C o v a l e n t l y b o n d e d m a t e r i a l s a r e l e ss dense than metallic or ionically bonded ones because covalent bonds are directional in nature whereas metallic and ionic are not; when bonds are directional, the atoms cannot pack together in as dense a manner, yielding a lower mass Concept Check 2.3 Q u e s t i o n : Offer an explanation as to why covalently bonded materials are generally less dense than ionically or metallically bonded ones. A n s w e r : C o v a l e n t l y b o n d e d m a t e r i a l s a r e l e ss dense than metallic or ionically bonded ones because covalent bonds are directional in nature whereas metallic and ionic are not; when bonds are directional, the atoms cannot pack together in as dense a manner, yielding a lower mass density. Chapter 3 Structures of Metals and Ceramics Concept Check 3.1 Q u e s t i o n : Table 3.4 gives the ionic radii for K + and O 2- as 0.138 and 0.140 nm, respectively. ( a ) W h a t w o u l d b e t h e c o o r d i n a t i o n n u m b e r f o r e a c h O 2- ion? ( b ) B r i e f l y d e s c r i b e t h e r e sulting crystal structure for K 2 O. ( c ) E x p l a i n w h y t h i s i s c a l l e d t h e a n t i f l u o r i t e s t r u c t u r e . A n s w e r : ( a ) F i r s t , l e t u s f i nd the coordination number of each O 2- ion for K 2 O. Taking the cation-anion radii ratio r K + r O 2- 0.138 nm 0.140 nm 0.986 From Table 3.3, the coordination number for oxygen is eight. ...
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