Review Chapter 9: The Basics of Chemical Bonding

Transcription

1 Review Chapter 9: The Basics of Chemical Bonding Chemistry: The Molecular Nature of Matter, 6 th edition By Jesperson, Brady, & yslop Chapter 9 Concepts! Know the difference between an ionic and covalent bond! Electronegativity:! Identify polar bonds and estimate relative dipole moments! Ionic Bond:! Energetics of ionic bonding: lattice energy! Predict possible ionic compounds! For transitions metals predict ions that will have half, full, or empty d-orbitals! Covalent Bond:! Draw lewis dot structures! Predict most reasonable lewis dot structure! Formal charges! Electronegativity! Identify possible reasonable resonance structures! Draw hybrid resonance structures! Understand electron delocalization & stability from it.!"

2 Covalent vs Ionic Bonds Ionic Bonds result from electrostatic attraction between a cation and anion: metal-nonmetal (with the exception of N 4 + and 3 + cations). Covalent bonds result from the sharing of electrons between two atoms: nonmetal-nonmetal. #$"" " " "%" Ionic Bonds Covalent Bonds Ionic Bonds Lattice Energy For a stable ionic compound to form the potential energy must be lowered. " Lattice Energies are usually very large negative numbers. " Lattice Energies always exothermic Transition Metals ard to predict ions electron configurations, but transition metal ions with exactly filled or half-filled d subshells are extra stable and therefore tend to form. " This is transition metals form multiple oxidation states " E q q 1 2 '()*(+,-."*/"12324+$52."362"7(3258/*"25249:"(;"3("$(5."<= > "/51" kr =!?".27/4/321",:"/"1$.3/5@2"<4?A"6242"B"$."/"74(7(48(5/*$3:"@(5.3/53C" &"

3 Electronegativity & Polar Bonds! +!! + on = +.17! on =.17!""#!$!%"# &!'!"# ( %! µ = q! r Atoms participating in covalent bonds will not share electron density equally if they have a difference in electronegativities of between.5 and 1.7. Drawing Lewis Dot Structures Step [1] Step [2] Step [3] Step [4] Determine the valence electrons for each element and draw the lewis symbol. Count the valence electrons. The sum gives the total number of e! that must be used in the Lewis structure. For each atom the number of bonds = 8 valence electrons. Arrange the atoms next to each other that you think are bonded together. Place and halogens on the periphery, since they can only form one bond. Arrange the electrons around the atoms. Place one bond (two e! ) between every two atoms. Use all remaining electrons to fill octets with lone pairs, beginning with atoms on the periphery.

4 Drawing Lewis Dot Structures >C )*+,+-.,!/-12-1+"E"/44/ "(;"/3(+.C""" 3+4-.,!.-56"" F.)/**:"9$G25"4.3" IC &C LC MC D4/"$5".$59*2",(51." %(4+"1(),*2",(51." The ctet Rule When atoms form covalent bonds, they tend to share sufficient electrons so as to achieve outer shell having eight electrons Exceptions olds rigorously for second row elements like C, N,, and F B and Be sometimes have less than octet Be 2, B 3 2 nd row can never have more than eight electrons 3 rd row and below, atoms often exceed octet

5 Formal Charges & Reasonable Structures S A5/-!)-.<,+!B+C8/!)-12-1+" >C #(2.3"7(..$,*2";(4+/*"@6/492."/42",2.3"!C **"%'"#"" > " IC 5:"529/8G2"%'"(5"+(.3"2*2@34(529/8G2"2*2+253" S Resonance Stabilization = Resonance Structures " D.C84E!F55=!G+/54.42+!)-12-1+/!! 1. All must be valid Lewis structures 2. nly electrons are shifted - Usually double or triple bond and lone pair - Nuclei can't be moved - Bond angles must remain the same Resonance ybrid Resonance Structures are equivalent lewis dot structures: - Atom connectivity does not change (ie, nuclei stay the same) - nly electrons change, ie, # of bonds between atoms can rearrange ybrid Resonance Structures show how electrons are delocalized over the molecule, the more atoms that are participating in the delocalization the more stable the molecule is. 4. Number of unpaired electrons, if any, must remain the same 5. Major contributors are the ones with lowest potential energy (see above) 6. Resonance stabilization is most important when delocalizing charge onto two or more atoms

6 Coordinate Covalent Bonds + N + + N N + B N B Problem Set A >C N1258;:"362"@(G/*253"/51"$(5$@",(51.P" /C '/%! ",C ''* Q/RS" 1C QS & QR I"!C T6$@6"$(5$@".(*$1"$."*$B2*:"3("6/G2"362".+/**2.3"2U(3624+$@"*/V@2"25249:W" #$'*X"'.'*X"Q/'*A"Y'*" IC T6/3"$(5"$**";(4+";(4"2/@6"2*2+253W"D4/"362"2*2+253."*2$.".:+,(*"!"#" 4$32"362"$(5-."2*2@34(5"@(59)4/8(5C" a. I!,C J" &C J421$@3"362"$(5$@"@(+7()51"36/3"$**";(4+",23225"362";(**($59P" /C "*)+$5)+"<*?"/51"'6*(4$52"<'*?",C [34(58)+"<[4?"/51"\4(+$52"<\4?"

7 Problem Set B/C LC /C ' M S M",C ' L S '! S'* I R!" 1C '! S^Q" 2C 'S! R I" ;C QS & 'Q" MC T6$@6"6/."362"*2/.3"7(*/4",(51W"S'*A"S%A"SNA"S\4C" ^C `C D4/"I"42.(5/5@2".34)@3)42."(;"Q'R a C"bG/*)/32"362";(4+/*"@6/492."(5" 2/@6"/51"12@$12"6$@6"$."362",2.3".34)@3)42C" cc D4/"362",2.3"*2$.".34)@3)42";(4"362";(**($59P"" a. 4 b. XeF 4 c. I 3 d. BrF 5 " >C N1258;:"362"@(G/*253"/51"$(5$@",(51.P" /C '/%! "I5482!,C ''* &"" Q/RS"I5482J!RS a "/"7(*:/3(+$@"$(5"$36"@(G/*253",(51." 1C QS & QR I ""I5482J!QS &d "/51"QR Ia "/42"7(*:/3(+$@"$(5."$36"@(G/*253",(51. " (K 3/3,J!,2@/).2"'."6/."362"*/492.3"4/1$).A"36242;(42"4"*/492"/51"b"*2.."529/8G2C" IC T6/3"$(5"$**";(4+";(4"2/@6"2*2+253W"T4$32"362"$(5-."2*2@34(5"@(59)4/8(5"and the lewis symbol. #"#" #" a. [Kr] 5s 2 4d 1 5p 6 #" I! #" #"#" Z,#" b. [Kr] or [Ar]"&.! "I1 >] "&7 eq2f"i.! "I7 M" P &C J421$@3"362"$(5$@"@(+7()51"36/3"$**";(4+P" /C *'* I",C [4\4!"

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