chuyen de lien ket hoa hoc

8/3/2019 Chuyen de Lien Ket Hoa Hoc

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Li n k t h a h c

Tr- ng chuy n L Qu n - Nng 1

Ch-ng III : lin kt ho hc!1. Tng quan v lin kt ho hc

I. Phn t v lin kt ha hcPhn t l ht vi m i di n cho cht v mang y t nh cht ho hc ca cht. Trong

t nhin ngo i cc kh hi m tn t i trng th i ph n t mt nguyn t, nguyn t ca c cnguyn t khc lun c xu h-ng kt hp vi nhau to to ra phn t c hai hay nhiunguyn t. S k t hp n y nh m t n c u trc mi bn vng hn, c nng l-ng th p hn.Ng-i ta gi s k t hp gia cc nguyn t l lin k t ho hc v nh- vy theo quan imhin nayphn t gm mt s c gii hn cc ht nhn nguyn t v cc electron t-ng tc vinhau v -c phn b m t cch xc nh trong khng gian to thnh mt cu trc bn vng.

Trong gi o tr nh n y, l thuy t tng quan v c c lo i lin k t ha hc -c x y dng trn thuyt electronha tr ca Lewis-Kossel-Langmuir m nn tng l qui tc bt t. Tuy nhin, thuy t n y cn nhiu h n ch dokhng cho thy b n ch t cc lo i lin k t v ch gi i th ch -c c u to v t nh cht ca cht trong mt str-ng hp n gi n... Do v y, trong mt s lo i lin k t, vic gi i th ch s h nh thnh lin k t cng nh- t nhcht ca ph n t -c kt hp vi mt s l thuy t hi n i hn.

II. Cc khuynh h-ng to lin kt ho hc1. Electron ho trElectron ho tr l electron c kh n ng tham gia to lin k t ho h c

Cc nguyn t nhm A c s electron ho tr b ng s electron lp ngoi cng, cc nguynt nhm B c s electron ho tr b ng s electron c trong c c ph n lp (n-1)dv ns.

2. Cng thc LewisCng thc Lewis l lo i cng thc cho bi t s electron ho tr ca nguyn t, trong

h t nh n v cc electron lp trong -c bi u di n b ng k hi u ha hc ca nguyn t ,cn mi electron ha tr -c bi u di n b ng mt d u ch m (.) quanh nguyn t (c ph nbi t gia electron cp i v c thn). Mi cp electron tham gia lin kt hoc t do cnc th -c bi u di n bng mt on gch ngang (-)

V d :IA IIA IIIA IVA VA VIA VIIA VIIIA

Chu k 2Li . eB : : B . :

.

.

C : ..

.

N :.

.

O : :..

..

F . :..

..

Ne :

hocLi . eB B .

.

.

C ..

.

N .

.

O

F .

Ne

3. Cc khuynh h-ng h nh thnh lin k t - Qui tc bt t (Octet)Nh- trn ni, s h nh th nh lin k t l nh m t c u trc bn vng hn. Thc t

cho thy trong t nhin cc kh him c th tn t i d ng nguyn t t do, iu n y cho

th y c u trc nguyn t kh hi m l mt c u trc bn. Trn c s n y, ng-i ta cho rngkhi tham gia lin k t t cu trc bn cc nguyn t c n ph i lm cho lp v cachng c c u trc ging lp v kh hi m g n k. C hai gi i php t n c u trc n yl dng chung hoc trao i c c electron ho tr.

Nhng iu ni trn l ni dung ca qui tc bt t : "Khi tham gia lin k t ho hc ccnguyn t c khuynh h-ng hoc dng chung electron hoc trao i electron t ncu trc bn ca kh hi m bn cnh vi 8 hoc 2 electron lp ngoi cng".

V d : H. + ...

..

Cl : H:..

..

Cl : H-Cl

Na. + ...

..

Cl : Na+ Cl- NaCl

(28 1) (2 8 7) (28) (2 8 8)

nNa. nNa+ + ne-


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Li n k t h a h c


+ + + +

+ + + +

+ + + +

cationkimlo i

electron t do

III. s phn loi cc Lin kt ho hc1. nh ngh a

a. Lin kt cng ha tr : L loi lin kt ha hc -c h nh th nh bi 1, 2 hay nhiuelectron chung.V d : H:H H2

O::O O2

H:O:H H2Ob. Lin k t ion : L lo i lin k t ha hc -c h nh th nh bi lc ht t nh i n gia c c

ion mang i n t ch tr i d u (gia cation v anion)V d : Na+Cl- NaCl

NH4+NO3

- NH4NO3

c. Lin k t kim loi : L lo i lin k t ha hc -ch nh th nh bi lc ht t nh i n gia c c cationkim loi nm nt mng tinh th v cc electront do di chuyn trong ton b m ng l-i tinh thkim lo i.

2. So snhLin kt cng ha

trLin k t ion Lin k t kim loi

Bn cht lc lin kt T nh i n (electronchung v h t nh n)

T nh i n (cation vanion)

T nh i n (cation velectron t do)

Khuynh h-ng Dng chung electron Trao i electron Dng chung electronT nh nh h-ng C t nh nh h-ng Khng nh h-ng Khng nh h-ng

3. i t-ng h nh thnh lin k ta.Lin kt cng ha tr : Th-ng h nh thnh gia cc nguyn tphi kim

V d : H-H, O=O, H-Cl, O=C=O...

b.Lin k t ion : Th-ng h nh thnh gia cc nguyn tkim loi v phi kim in h nhV d : Na+Cl-, Mg2+F2

-, K2+O2-...

c. Lin kt kim loi : Th-ng h nh thnh gia cc nguyn tkim loi

IV. Mt s i l-ng c tr-ng cho lin kt ha hc1. di lin kt (d) : l kho ng c ch gia hai h t nh n ca hai

nguyn t lin k t trc ti p vi nhau.V d : Trong phn t n-c , dO-H = 0,94

d i lin k t gia hai nguyn t A-B c th t nh g n ng b ngtng bn k nh ca hai nguyn t A v B.

2. Gc lin k t : l gc t o bi hai na -ng thng xu t ph t t h tnhn ca mt nguyn t v i qua ht nh n ca hai nguyn t kh c lin k t trc tip vi hainguyn t trn.V d : Trong phn t n-c ,

3. Nng l-ng lin k t (E):Nng l-ng lin k t A-B l nng l-ng cn cung cp ph v hon ton lin k t A-B(th-ng -c qui v1 mol lin k t - kJ/mol hoc kcal/mol).EH-H = 103 kcal/mol : H2 2H H = 103 kcal/mol.

Nng l-ng lin k t (n ng l-ng phn li lin kt), v tr tuy t i, ch nh b ng nng l-ngh nh thnh lin k t. Tng nng l-ng cc lin k t trong phn t b ng nng l-ng phn lica phn t .

HOH =104o28'

O0,94

104

o

28'H H


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Li n k t h a h c


2. lin kt cng ha tr

A. l thuyt phi c hc l-ng t

(Thuy t electron ha tr Lewis - Langmuir)1. S h nh thnh lin k t cng ha tr! Khi h nh th nh lin k t cng ha tr, c c nguyn t c khuynh h-ng dng chung cccp electron t n cu trc bn ca kh hi m k bn (vi 8 hoc 2 electron lp ngo icng).! C c cp electron dng chung c th do sgp chungca hai nguyn t tham gia lin k t(cng ha tr thng th-ng) hoc ch do mt nguyn t b ra dng chung (cng ha tr phitr)

S electron gp chung ca mt nguyn t th-ng bng 8-n (n : s th t ca nhm nguyn t).Khi h t kh nng gp chung, lin k t vi c c nguyn t cn li -c h nh thnh bng cpelectron do mt nguyn t b ra (th-ng l nguyn t ca nguyn t c m i n nh hn).

V d :Cng thc ph n t Cng thc electron Cng thc c u t oH2O H:O:H H-O-HSO2 :O::S:O: O=SO

2. Cng thc cu to ca mt s loi hp cht thi t lp trn thuyt electron ha tr.a. Hp cht cha hidro

CH4

H

C HH

H NH3

H

N

H H N2H4

H

N

H

N

H

H

H2O H O H H2O2 H O O H HCl H Cl

b. Oxit (L-u : Trt t lin k t trong oxit dng X2On l O(n-1)/2XOX O(n-1)/2)CO : C O

SO2O S O

N2O3O N OO N

Cl2O : Cl O Cl

CO2 :O C O

SO3 : O

O

O

N2O5

O N

O

O

O

N

O

Cl2O7:

O

Cl

O

O Cl

O

O

OO

c. Hidroxit (L-u : Trt t lin k t trong oxit dngHnXOm l (HO)nXOm-n)

H2CO3

HO

HO

O

H2SO4

HO

S

HO

O

O

HNO3

O

NHO

O HClO4

HO Cl

O

O

O

d. Mui : Cng thc ca mui c th xy dng t c ng thc axit t-ng ng, trong H+/axit -c thay th bi Mn+/mui.

Na2CO32Na+

Ca(NO3)2Ca2+

3. N hng hn ch ca l thuy t phi c hc l-ng t! Khng cho th y bn ch t ca lin k t cng ha tr! Khng cho thy s nh h-ng khng gian ca lin k t v nh- vy khng th gii th ch cu to

h nh hc ca ph n t.

O 2-

C=OO

O-N=O -

O 2


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Li n k t h a h c


! Khng gi i th ch -c mt s cng thc cu to trong lin kt cng ha tr khng phi-c h nh thnh t cp electron m l i xu t hi n cc s l electron chung, cng nh- cc cngthc trong qui tc bt t khng -c tha mn (s electron lp ngo i cng ca nguyn t nhhn hoc ln hn 8).

! Khng gi i th ch -c lin kt "cng ha tr nhiu tm khng nh x" nh- trong phn tbenzen C6H6...

B. l thuyt c hc l-ng tI.Thuyt VB(ValentBond - Lin k t ha tr)Heitler-London kh o s t phn t H2 trn c s ca c hc l-ng t, sau m rng v phttrin thnh ph-ng php lin k t cng ha tr (thuy t VB) p dng cho mi ph n t. Trongph n n y khng cp n kh a c nh ton-l ca ph-ng php m ch cp n ph-ngph p nh t nh gi i th ch cc v n v lin k t cng ha tr, m ch y u l cc lin k t nhx.

1. Thuy t VB v s h nh thnh lin kt cng ha tr .! Khi hai nguyn t tham gia lin kt l i gn nhau s xu t hi n lc ht t nh i n gia h tnh n nguyn t n y vi lp v electron ca nguyn t kia l m cho c c obitan "xen ph" vo

nhau mt ph n. Vi s xen ph n y, mt i n t ch m kho ng gia h t nhn hainguyn t (mang i n t ch d-ng) t ng ln, lm t ng lc ht gia electron trong vng xenph vi hai ht nh n, lc ht ny c n b ng vi lc y t-ng h ca hai h t nhn, giu choh t nhn hai nguyn t lin k t vi nhau : lin k t ha hc -c h nh th nh. C n thy r ng,khi cc obitan "xen ph" vo nhau electron khng cn thuc v m t nguyn t na, chng dichuy n trong mt obitan mi ca c hai nguyn t. Theo Pauli, obitan mi h nh th nh n y chcha ti a hai electron v hai electron ny ph i c spin ng-c du. Nh- v ymi lin ktcng ha tr -c -c h nh thnh bng cch xen ph hai obitan nguyn t c electronc thn ca hai nguyn t lin kt, hai electronc thn tham gia lin kt phi c spinng-c du.! Lin k t gia hai nguyn t c ng bn nu mc xen ph ca c c obitan c ng ln, dov y s xen ph ca cc obitan tu n theo nguyn l xen ph cc i : lin k t -c phn btheo ph-ng no m mc mc xen ph cc obitan lin k t c gi tr cc i.

V d :H2 H:H H-H

H HH : 1s1

HCl H:Cl H-ClH Cl

Cl:3s23p5

Cl2 Cl:Cl Cl-ClCl Cl

2. Thuy t VB gii th ch nhng hn ch ca thuy t electron ha tr! Vi ph-ng ph p gi i th ch s h nh th nh lin k t cng ha tr tr nh by trn, thuy tVB cho thy lin k t cng ha tr -c h nh th nh nh t-ng tc t nh i n gia c celectron chung (mang i n t ch m)vi ht nh n hai nguyn t (mang i n t ch d-ng).! Theo thuyt VB lin k t -c phn b theo ph-ng no m mc mc xen ph ccobitan lin kt c gi tr cc i, nh- v y lin k t cng ha tr l mt lin k t c t nh nhh-ng v ph n t to t c c lin k t cng ha tr s c mt cu t o h nh hc x c nh. Cuto h nh hc ca cc ph n t s -c kh o s t trn c s ca mt l thuy t i km vithuy t VB l thuyt lai ha c c obitan nguyn t.! Theo thuyt VB, c u trc bn khng nh t thi t ph i ging vi c u trc ca kh him. Khihai nguyn t lin k t vi nhau b ng cch xen ph hai obitan cha electron i song spinng-c du) l m cho nng l-ng ca h thng gi m, c u trc c to ra l bn hnso vi c u trc ca cc nguyn t t-ng ng ng vi mc n ng l-ng thp hn. Nh- vy cth gii th ch -c lin k t cng ha tr trong mt s phn t m c u trc ca nguyn tkhng ging cu trc kh hi m.


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Li n k t h a h c


3. Thuyt VB v v n ha tr ca nguyn t trong hp cht cng ha tr! Cng ha tr ca mt nguyn t (ha tr nguyn t) bng s lin kt m nguyn t cth to -c vi cc nguyn t khc.

V d : Trong CO2 (O=C=O) nguyn t C v O l n l-t c cng ha tr bng 4 v 2.! Theo thuyt VB, to -c mt lin kt cng ha tr, nguyn t s dng mtelectron c thn ca chng. Nh- vy, c th ni r ng cng ha tr ca mt nguyn t bng

s electron c thn ca nguyn t dng tham gia lin k t.! Cng theo thuy t VB, khi tham gia lin k t cc nguyn t c th b "k ch th ch". S k chth ch n y c nh h-ng n cu h nh electron ca nguyn t , cc electron cp i c tht ch ra v chi m c c c obitan cn trng trong cng mt lp. Nh- vy s electron c thnca nguyn t c th thay i v c ng ha tr ca nguyn t c th c gi tr khc nhau trongnhng hp cht khc nhau (xem b ng 1).

B ng 1 : S electron c th n c th c ca nguyn t thuc phn nhm ch nhNhm Cu h nh electron ha tr S e-

c thn

ns2 IIA

X* 2

ns2np1 IIIA

X*

1, 3

ns2np2 IVA

X*

2, 4

ns2np3

X*

VAT chu k 3

X*

3, 5

ns2np4

X*

VIAT chu k 3

X*

2, 4, 6

ns2np5

X*

X*

VIIAT chu k 3

X*

1, 3, 5, 7

V d 1 : Cng ha tr ca l-u hunhH2S (S ha tr 2)

H-S-HSO2 (S ha tr 4)

O=S=OH2SO4 (S ha tr 6)

V d 2 : Cng ha tr ca ClHOCl (Cl ha tr 1)

H-O-ClHOCl2 (Cl ha tr 3)

H-O-Cl=OHOCl3 (Cl ha tr 5) HOCl4 (Cl ha tr 7)

4. Bc lin ktBc lin k t l s lin k t cng ha tr (s cp electron chung) gia hai nguyn t .

a. Lin kt b c mt (lin k t n) : ch c mt lin k t cng ha tr gia 2 nguyn t

H-O OS

H-O O

OH-O-Cl

O

OH-O-Cl = O

O


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Li n k t h a h c


V d : H-H, H-Clb. Lin k t b c hai (lin k t i) : c hai lin k t cng ha tr gia 2 nguyn t

V d : O=C=Oc. Lin k t bc ba (lin k t ba) : c ba lin k t cng ha tr gia 2 nguyn t .

V d : NN, H-CC-HCc lin i v ba cn -c gi chung l lin kt bi.

! Khi s electron chung cng ln, lc ht t nh i n gia electron vi h t nh n ca hainguyn t c ng m nh, bn lin k t t ng cn khong c ch gia hai tm nguyn t gi m.

Do v y, khi b c lin k t c ng ln th nng l-ng lin kt cng ln v di lin kt cngnh.

V d :Phn t : C-C C=C CCE (kcal/mol): 83 143 194dC-C () : 1,54 1,34 1,2

5. Lin kt xichma () v lin kt pi ()Ty theo c ch xen ph c c obitan nguyn t m lin kt cng ha tr to thnh c bn

khc nhau. Trn c s n y ng-i ta phn bi t lin k t cng ha ha tr th nh hai lo i ch nhl lin k t xichma () v lin kt pi ().

a. Lin kt Lin k t l loi lin kt cng ha tr -c h nh thnh bng ph-ng php xen phng trc cc obitan nguyn t, vng xen ph nm trn trc lin k t.Lin kt c c c loi s-s , s-p , p-p ,...

s s s p p pLin k t th-ng bn, do c vng xen ph ln v cc nguyn t c th quay t do xungquanh trc lin k t m khng ph v lin k t ny.

b. Lin kt Lin k tl lo i lin kt cng ha tr -c h nh thnh bng ph-ng php xenph song song trc cc obitan nguyn t, vng xen ph nm hai ph a so vitrc lin k t.Lin kt c cc lo i p-p ,p-d ,...Lin k t km bn, do c v ng xen ph nh v c c nguyn t khng th quayt do xung quanh trc lin k t m khng ph v lin kt ny.

Lin kt n lun l lin kt, lin k t i gm 1v 1v lin k t ba gm 1v 2.

6. Lin k t cng ha tr phn cc v khng phn cc! Trong phn t H2 (H:H) do m i n ca hai nguyn t H b ng nhau nn xc su t cmt ca electron chung ln nh t l kho ng gia h t nh n hai nguyn t, s ph n b i nt ch trn hai nguyn t H l b ng nhau, ng-i ta gi lin k t gia hai nguyn t H trong ph nt H2 l lin k t cng ha tr khng phn cc. Trong phn t HCl (H :Cl) do m i n caCl (3,0) ln hn m i n ca H (2,1) nn electron chung b ht l ch mt ph n v ph anguyn t Cl (H :Cl), x c su t c mt ca electron v ng g n nguyn t Cl s nhiu hn,nguyn t Cl mang mt ph n i n t ch m (-) v ng-c l i nguyn t H mang mt ph nin t ch d-ng (+), ng-i ta ni lin k t gia H v Cl trong phn t HCl l lin kt cngha tr phn cc.! Lin kt cng ha tr khng phn cc l loi lin k t cng ha tr trong electronchung ch nh gia ht nhn hai nguyn t. Lin k t cng ha tr khng phn cc h nh

th nh gia cc nguyn t ca cng mt nguyn t nh- trong c c n ch t H2, N2, O2, Cl2, ...! Lin k t cng ha tr phn cc l loi lin k t cng ha tr trong electron chung l chmt phn v ph a nguyn t c m i n ln hn, nguyn t ny s mang mt phn i n


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Li n k t h a h c


t ch m v ng-c li. Lin kt cng ha tr khng ph n cc h nh th nh gia c c nguyn tca hai nguyn t khc nhau (hi u m i n gia hai nguyn t c gi tr trong kho ngt 0 n 1,7), nh- lin k t trong c c ph n t HCl, H2O, SO2, ... Ng-i ta biu din s phncc b ng mi tn trn g ch ngang lin k t theo chiu t nguyn t c m i n nh nnguyn t c m i n ln.

7. S lai ha cc obitan nguyn t! Trn cc lun i m thu n ty ca thuy t VB s khng gi i th ch ng cu t o h nh hcca phn t. V d nh- trong phn t n-c (H-O-H), hai lin k t cng ha tr -c h nhth nh bi s xen ph hai obitan p ca O vi hai obitan s ca hai nguyn t H, nh- vy gc link t HOH ph i l 90o (hai obitan p ca O vung g c vi nhau). Nh-ng thc t gc lin kt n yli bng 104o28'. gi i quy t vn ny, ng-i ta b sung thm vo thuy t VB mt githuy t mi c tn l thuyt lai ha cc obitan nguyn t.! Thuy t lai ha cho r ng mt s obitan c mc n ng l-ng gn bng nhau khi tham gia

lin k t c xu h-ng t hp vi nhau t o ra cc obitan lai ha c n ng l-ng thp hn,lin kt h nh th nh bi s xen ph cc obitan lai ha s bn vng hn.! S obitan lai ha to thnh bng s obitan nguyn t tham gia lai ha v cc obitan laiha to ra c nng l-ng t-ng -ng. Bng 2 tm t t mt s d ng lai ha th-ng gp.

Bng 2 : Cc tr-ng hp ch y u ca s lai ha cc obitan nguyn tKhiu

S lai ha Phn b khng gian ca c c obitan lai ha

spp

sps

180o -ng th ng

sp2 sp2s

120o Tam gic

sp3p sp3

s109o28' T di n

sp3dd

p sp3d

s

L-ng th p y tam gi c

sp3d2d

p sp3d2

s

B t din

! Kiu lai ha ca nguyn t c th x c nh da trn gi tr thc nghi m ca gc lin kt,v d gc lin k t HOH trong ph n t n-c c gi tr 104o28' g n vi gi tr 109o28' nh- v ynguyn t O trong ph n t H2Olai ha sp

3. Ng-i ta cng d o n ki u lai ha ca nguyn ttrn l thuy t b ng tng s lin k t m nguyn t to ra v s cp electron t do canguyn t (H). Gi tr ca H t nh -c b ng 2, 3, 4, 5, 6 t-ng ng vi cc trng thi lai hasp, sp2, sp3, sp3d, sp3d2.

V d: H-O-H, HO = 2+2 = 4 O lai ha sp3.

O=SO, HS = 2+1 = 3 S lai ha sp2

- +A B (A < B)


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Li n k t h a h c


O=C=O, HC = 2+0 = 2 C lai ha sp

! D-i y l mt s v d v s h nh th nh ph n t trn c s k t hp thuy t VB vthuyt lai ha cc obitan nguyn t :

CH4 (C lai ha sp3) CH2=CH2 (C lai ha sp

2) CHCH (C lai ha sp)H

H HH

H HH H H H

8. Mt s t nh cht ca phnta. Cu trc h nh hc

C mt s ph-ng ph p khc nhau gi i th ch cu trc h nh hc ca ph n t nh-ph-ng php m h nh s y gia cc i electron v ha tr - VSEPR, ph-ng php mh nh lin k t b un conghoc ph-ng php m h nh lai ha cc obitan nguyn t. Trong b iny c c c u trc h nh hc ca ph n t -c xem xt trn c sm h nh lai ha cc obitannguyn t.

Bng d-i y l mt s m h nh cu trc h nh hc ca ph n t :

-ngthng

Ch V Tamgic

phng

Thptamgic

T din L-ngthp

y tamgic

Vungphng

Thpvung

B tdin

Mi lo i lai ha c kh nng t o ra mt hay mt s c u trc no :! Lai ha sp : to cu trc -ng thng (nh- trong c c ph n t BeH2, ZnCl2, CO2,C2H2,

...)V d :

H C C H

! Lai ha sp2 : to c u trc ch V(nh- trong cc phn t SO2 , O3 , ...), tam gic phng(nh- trong c c ph n t v ion : BF3, SO3, HNO3 ,C2H4 , NO, NO3

-, CO32-...).

V d :

O

S

O

H-O N+

O

O

! Lai ha sp3 : to cu trc ch V(nh- cc phn t H2O , H2S, ...), thp tam gic (nh-NH3, H3O

+ , ...) v t din (nh- trong c c ph n t v ion: CH4, CCl4, NH4+, PO4

3-, SO42-,

ClO4-...).

V d :

H

O

H

N

H H

H

H

C

H

H

H

! Lai ha sp3d : to cu trc thng (nh- XeF2), ch T(nh- ClF3), l-ng thp tam gic(nh- trong ph n t PCl5, ...).V d :


9/22

Li n k t h a h c


F Xe F

F Cl F

F

ClP

Cl

Cl

Cl

Cl

! Lai ha sp3d2 : t o c u trc vung phng (nh- trong phn t XeF4, ...), thp vung (nh-

trong phn t BrF5,...) v cu trc bt din (nh- trong SF6, AlF63-, SiF62-...).V d :

F

Xe

F

F

F

F

BrF

F

F

F

F

S

F

F

F

F

F

b. S phn cc ca phn t! L-ng cc i n : L-ng cc i n l mt h gm hai i n t ch +q

v -q c ch nhau mt khong c ch l. L-ng cc in -c c tr-ng

bng i l-ng momen l-ng cc vi nh ngh a momen l-ngcc bng t ch ca i n t ch q v cnh tay n l.

= ql.

Trong h SI momen l-ng cc -c t nh b ng Cm (coulomb.met). Vi ph n t domomen l-ng cc c gi tr nh nn ng-i ta th-ng t nh theo D (Debye) vi qui -c :

1D =3

1.10-29Cm

! L-ng cc lin kt : Trong lin k t ion hoc lin k t cng ha tr phn cc i n t chphn b khng ng u trn hai nguyn t tham gia lin k t, trng t m i n t ch mlch v ph a nguyn t c m i n ln hn v trng t m i n t ch d-ng lch v

ph a nguyn t c m i n nh hn. Nh- vy, mi lin k t ion hoc lin k t cngha tr phn cc l mt l-ng cc i n v c mt momen l-ng cc xc nh -c gil momen l-ng cc lin kt. Lin k t ph n cc c ng mnh th momen l-ng cc cngln.

V d :Lin kt H > F H > Cl H > Br H > I (D) 1,83 1,08 0,82 0,44

! L-ng cc phn t : Trong vic kh o s t l-ng cc phn t, ng-i ta tha nh n thuct nh cng t nh ca momen l-ng cc lin k t v coi momen l-ng cc ca phn t ltng vect cc momen l-ng cc lin k t.

V d :

Vi ph n t CO2 : =O C = O = 0

Vi ph n t H2O : HO

H 0 ( = 1,84D)

! Vic kho st momen l-ng cc ph n t l mt thng s c n thi t cho vi c nghin cut nh cht ca lin k t (khi cng ln, t nh ion ca lin k t cng mnh), c u trc h nhhc ca ph n t cng nh- cc t nh ch t v t l , ha hc ca mt cht.

c. T t nh ca phn t! Cht thun t : Ch t thun t l nhng ch t b ht bi nam chm. V mt cu to, ph n

t ca cc ch t n y c electron khng ghp i (electron c thn).

-ql

+qL-ng cc i n


10/22

Li n k t h a h c


V d : NO2 l mt ch t thu n t do trong c u to cn mt electron c th n trn

nguyn t N : ONOo

= ! Cht nghch t : Ch t nghch t l nhng ch t b y bi nam chm. V mt c u to,

ph n t ca cc ch t n y khng c electron c thn.! Vic nghin cu t t nh ca phn t l m s ng t hn c u t o ca ph n t . V d nh-

thc nghi m cho th y oxi (O2) l mt cht thun t, t-ng -ng vi cu to phn tphi c electronc th n. Nh- v y, cch l gi i theo thuyt electron ha tr hoc theo

thuyt cng ha tr (VB) (cng thc ca phn t oxi (O2) c dng

= OO ch gm cc

electron ghp i) l khng ng. Cng thc ng ca O2 -c gi i th ch trn c s cathuyt obitan phn t (MO) s xt n phn sau.

II.Thuyt MO(Molecular Orbital - Obitan phn t)

Thuy t VB v MO (Hund, Mulliken, Lenard-Jones, 1927-1929) u da trn l thuyt c hcl-ng t gi i th ch s h nh th nh lin k t v t nh ch t ha hc ca phn t , tuy nhin c cht v n ca hai thuy t ny g n nh- tri ng-c nhau. Thuy t VB tha nh n s t nh c l pca c c nguyn t trong phn t, lin k t -c h nh t cc obitan nguyn t khc nhau. Thuy tMO ph nh n s t n t i c lp ca cc nguyn t trong phn t, c c electron trong ph n tkhng cn thuc v c c obitan nguyn t m thuc v cc obitan chung gi l obitan ph n t.Trong b i ny chng ta tho lu n k t qu thu -c t ph-ng php MO.

1. Cc lun im ch nh ca thuyt MO! Trong ph n t c c electron chuy n ng trong nhng obitan chung gi l obitan ph n t.

Cc obitan ph n t (c c MO) ny thu -c t s t hp tuyn t nh c c obitan nguyn t(atomic orbital - AO). Tng s MO thu -c bng tng s AO tham gia t hp.

! Cc MO thu -c c n ng l-ng kh c nhau -c h nh th nh mt gin nng l-ngc gi tr t thp n cao.

! Mi loi MO gm cc MO c n ng l-ng thp gi l MO lin k t ( hoc ) v MO cnng l-ng cao hn gi l MO ph n lin k t (* hoc *).

! C c electron ha tr ca nguyn t tham gia lin k t -c phn b v o c c MO tu n theonguyn l vng bn, nguyn l Pauli v qui tc Hund.

! Bc lin k t =2

1(s electron trn MO lin k t - s electron trn MO phn lin k t)

2. Thuy t MO v s h nh thnh lin kt cng ha tr.a. Phn t hai nguyn t dng A2.

! Chu k 1: C c nguyn t chu k 1 c AO duy nht 1s, nn trong phn t hai nguyn tdng A2 s c s t hp hai AO-s t o ra hai MO- c nng l-ng nh- gin d-i y :

E *1s

1s 1s

1sA A2 A

Trn c s gin ny ta c cu h nh ph n t :


11/22

Li n k t h a h c


H: 1s1 H2 : (1s)2 (*1s)

0, b c lin k t =2

1(2-0) = 1.

Hai nguyn t H lin vi nhau bng mt lin k t n : H-H

He: 1s2 He2 : (1s)2 (*1s)

2, b c lin k t =2

1(2-2) = 0.

Khng tn t i lin k t gia hai nguyn t He.

! Chu k 2 : Cc nguyn t ca cc nguyn t chu k 2 c 4 AO ha tr (2s, 2px, 2py v2pz), do v y trong ph n t hai nguyn t d ng A2 s t hp to 8 MO :- Hai AO-2s to ra hai MO- l 2S v

*2S

- Hai AO-2pZ t o ra hai MO- l Z v *Z

- Bn AO-2pX,Y t o ra hai MO- l X, Y v *

X, *Y.

i v i c c h O2, F2, (Ne2) nng l-ng cc MO -c phn b t ng d n theo th t :2S <

*2S < Z < X, Y <

*X,

*Y <

*Z (gi n A)

i v i cc h Li2, (Be2), B2, C2, N2 nng l-ng cc MO -c ph n b t ng d n theo tht :

2S < *2S < X, Y < Z <

*X,

*Y <

*Z (gin B)

E *Z *Z

*X *

Y *X

*Y

2p 2p 2p 2p 2p 2p 2p 2p 2p 2p 2p 2pX Y 2S

2S X Y

*

S *

S2s 2s 2s 2s

S S(Gin A) (Gin B)

Trn c s gin ny ta c cu h nh ph n t :F : [He] 2s2 2p5 Ph n t F2 c tng 14 electron ha tr ng vi c u h nh :

F2 : (2S)2 (*2S)

2 (Z)2 (X)

2 (Y)2 (*X)

2 (*Y)2 (*Z)

0

Bc lin k t =2

1(8-6) = 1

Hai nguyn t F lin vi nhau b ng mt lin k t n ( F-F )

O:[He] 2s2

2p4

Ph n t O2 c tng 12 electron ha tr ng vi c u h nh :

O2 : (2S)2 (*2S)

2 (Z)2 (X)

2 (Y)2 (*X)

1 (*Y)1 (*Z)

0

Bc lin k t =2

1(8-4) = 2

Hai nguyn t O lin vi nhau bng mt lin k t n v hai lin k t

mt electron ( O O hay OO!

"

)

b. Phn t hai nguyn t dng AB.i vi c c nguyn t chu k 2, s t hp ca hai AO-2s v su AO-2p to ra tm MO c tr tt

t ng d n mc nng l-

ng nh-

sau :2S < *2S < X, Y < Z <

*X,

*Y <

*Z

Trn c s ny ta c th kh o s t c u h nh ph n t ca cc phn t nh- NO, CO, ...hay c cion nh- CN -, NO+, NO-, CO+,...


12/22

Li n k t h a h c


! BO, CN, CO+ , c c ph n t v ion n y u c 9 electron ha tr ng vi c u h nh :(2S)

2 (*2S)2 (X)

2 (Y)2 (Z)

1

Bc lin k t =2

1(5-2)= 2,5

Ph n t c mt lin k t , mt lin kt v mt lin k t mt electron ( BA"

= ).! CO, NO

+

, CN-

, c c ph n t v ion n y u c 10 electron ha tr ng vi c u h nh :(2S)2 (*2S)

2 (X)2 (Y)

2 (Z)2

Bc lin k t =2

1(8-2)= 3

Ph n t c mt lin k t v hai lin k t ( BA ).! NO, ph n t n y c 11 electron ha tr ng vi c u h nh :

(2S)2 (*2S)

2 (X)2 (Y)

2 (Z)2 (*X)

1

B c lin k t =2

1(8-3)= 2,5

Ph n t c mt lin k t , mt lin kt v mt lin k t mt electron ( ON"

= ).

3. S cng h-ng - Lin k t nhiu tm khng nh xThc nghi m cho bit trong ion cacbonat CO3

2-c c gc t m u l 120o v cc lin k t c d i nh- nhau (1,31), di ny c gi tr trung gian gia lin kt n C-O (1,43 nh- trongph n t CH3OH) v lin k t i C=O (1,21 nh- trong phn t H2C=O) . Nh- vy cng thc -cvit nh- d-i y l khng ph hp do bc lin kt khc nhau s to ra d i v gc lin k t kh cnhau :

-O

C

-O

O

Gi i th ch v n n y, ng-i ta cho rng do t nh b nh ng ca 3 nguyn t O m link t C=O c th chuy n ha qua l i gia 3 nguyn t v nh- vy CO3

2- tn t i ng thi 3dng c u t o t-ng -ng (nh- c c cng thc a, b, c d-i y). Ng-i ta gi y l hint-ng cng h-ngv c c c u to y -c gi l cu to cng h-ng.

-O

C

-O

O

(a)

O-C

-O

O (b) -O

C O-

O

(c)

Ch nh xc hn - theo thuyt MO - trong ion CO32- c mt MO- h nh th nh do s t hp

ca 4 AO-p hay ni c ch kh c c mt lin k t khng nh x, m gii ta trn 4 nguyn

t ca phn t (xem cng thc d) vi b c lin k t ca mi lin kt C-O l3

4=

3

11

O C

O

O(d)

S cng h-ng t-ng t trn cn gp mt s tr-ng hp nh- HNO3, NO3-, PO43-, SO42-,ClO4

-, benzen C6H6...V d :


13/22

Li n k t h a h c


N

O

O

HO

S

O

O

OO

Theo thuyt MO, lin k t nhiu tm khng nh x khng ch xu t hin trong c c hcng h-ng , m cn c cc lin kt nhiu t m khng nh x. L thuy t v lin k tnhiu t m khng nh x gip gi i th ch -c lin k t mt s ph n t thiu cng nh- thaelectron.

V d : Trong phn t diboran tn t i hai lin k t khng nh x 3 tm (BHB)

B

H

H

H

H

B

H

H

B

H

H

H

H

B

H

H

B

H

H

H

H

B

H

H

2. lin kt Trong phn t phc

I. i c-ng v phc cht1. Khi nim" Phc cht l nhng hp ch t phc t p h nh th nh t nhng ph n t hay ion n gi n,

th-ng gm ion hay nguyn t trung tm (ht trung tm) v cc phn t , ion lin k t vi h ttrung t m (c cphi t - ligan).

V d : Fe(CO)5 , K2[CuCl4]" Ht trung tm trong ph n ln c c ph n t phc l nguyn t hay cation ca cc kim lo ichuy n ti p nh- Fe, Co, Ni, Fe2+, Fe3+, Co3+, Ni2+, Cu2+, Ag+, Au3+...

" Cc phi tc th l cc phn t trung ha (nh- CO, NH3, H2O,...) hay c c anion (nh- F-,

Cl-, Br-, CN -, OH-,...).- S phi t lin kt trc tip vi ht trung tm -c gi l s phi tr ca h t trung tm.

V d : Fe(CO)5 Fe c s phi tr bng 5K2[CuCl4] Cu

2+ c s phi tr bng 4.- c i m chung ca cc phi t l chng u c mt hay nhiu cp electron t do c khn ng to lin k t vi h t trung tm, s cp electron t do tham gia lin k t -c gi l s

rng ca phi t. Ty theo s cp electron t do ca phi t c kh n ng t o lin kt vi h ttrung tm m ng-i ta chia phi t th nhphi t mt rng hay nhiu rng:Phi t mt rngl phi t ch c mt cp electron ring tham gia lin k t t o phc.

V d nh- : Cl-, OH-, CN-, SCN-, NO2-, CH3COO

-...

hoc3

HN

,

OH2

,

NHC55

(piridin, vi t t t l pi),

OC , ...

Phi t nhiu rngl phi t c ng thi nhiu cp electron ring tham gia lin k t

V d nh- : ( )2222

HNCHNH

(etilendiamin - en) - 2 rng

( ) ( )222222

HNCHHNCHNH

(dietilentriamin-dien) - 3rng

H2C

H2CN N

H2C

H2C

CH2

CH2

COO-

COO-

-OOC

-OOC


14/22

Li n k t h a h c


(etilendiamin tetra axetat - EDTA) - 6 r ng" Cu to ca phc c th chia thnh 2 ph n, h t trung tm v cc phi t hp th nh cu ni

(t trong d u mc vung), ph n cn l i ca phc -c gi l cu ngoi.

V d :cuni

CuCl

icungo

K ][

42

icungo

NO

cuni

OHAl

)(])([3362

" Vic phn loi phc da trn mt s c s kh c nhau :

- Da trn s phi t ng-i ta chia th nhphc c s phi tr 2, 3, ..., 6.V d : [Ag(NH3)2]

+ (s phi tr 2)[HgI3]

- (s phi tr 3)...[Fe(CN)6]

4- (s phi tr 6)- Da vo lo i phi t c th chia th nhphc aqu (phi t l H2O),phc aminoacat (phit l NH3), phc hidroxo (phi t l OH

-), phc axido (phi t l gc axit), phc hn tp(cha 2 hay nhiu phi t khc nhau)...

V d : [Cr(H2O)6]Cl3 phc aqu[Cu(NH3)4]SO4phc aminoacatK2[Zn(OH)4] phc hidroxo ...

- Da v o i n t ch ca c u ni c th chia th nhphc cation (c u ni l ion d-ng),phcanion (c u ni l ion m), phc trung ha (cu ni l phn t trung ha).

2. Danh phpTn ca phc -c gi theo tr t t :

" Tn cation tr-c tn anion (khng ph n bi t ion c u ni hay c u ngo i)" Cc c u t ca c u ni -c gi theo trt t :

S phi t + Tn phi t + Tn ht trung tm! S phi t-c gi b ng s m Hilp (2 : di, 3 : tri, 4 : tetra, 5 : penta, 6 : hexa, 7 :

hepta, 8 : octa, ...)! Tn ca phi t:

- Phi t l anion : tn ca anion, thm ti p v ng "o"V d : Cl- cloro, CN- : xiano, OH- : hidroxo, SCN- : thioxianato, S2O3

2- : thiosunfato...- Phi t l phn t trung ha : mang cc tn ring.

V d : H2O : aquo, NH3 : amin, CO : cacbonyl ...- Trong phc hn tp, tn phi t -c gi theo tr t t : phi t l anion tr-c (c c anionv c c s nguyn t t ng d n, cc anion hu c theo tr t t b ng ch c i), sau nphi t trung ha (H2O, NH3, cc phi t v c , c c phi t hu c theo tr t t b ng chci).

! Tn h t trung tm -c gi b ng tn Latinh, c ch ti mc oxi ha (ghi b ng s Lam trong ngoc n). i vi c u ni l ion m, tn h t trung t m c thm tip v ng"at".V d : [Pt(NH3)2Cl2] Diclorodiamin platin(II)

[Ti(H2O)6]Cl3 Hexaaquotitan(III) clorua[Pt(NH3)4(H2O)2]Cl4 Diaquotetraaminplatin(IV) cloruaK2[PtCl6] Kali hexacloroplatinat(IV)K2[Zn(OH)4] Kali tetrahidroxozincat(II)

""#!$%&'!()*!*+,'-!./0'!*1!./23!1. Thuyt VB v phc" Cc lun im ch nh

! Mi phi t u c c c cp electron t do, trong khi cc h t trung t m (c c nguyn thay ion kim lo i chuy n tip) l i c cc obitan trng (obitan t do). S xen ph gia c cobitan mang cp electron t do ca phi t vi cc obitan t do lai ha ca ht trung t mh nh th nh cc lin k t cng ha tr phi tr . Nh- v y lin kt ha hc trong ph n tphc ch gm c c lin k t cng ha tr phi tr gia cc phi t v i h t trung tm.


15/22

Li n k t h a h c


! C u to h nh hc ca phn t phc ph thuc trng thi lai ha ca h t trung t m." Phc vi s phi tr khc nhau

Phc c s phi tr 2 : Th-ng l phc ca cc ion Ag+, Cu+, Au+, Hg2+ vi cc phi t nh-NH3, Cl

-, CN -, S2O32-...Trong phc n y cc h t trung tm th i lai ha sp nn phc cu h nh

-ng thng.V d : Phc [CuCl2]

-

Cu h nh ca Cu+

: 3d10

Trng th i lai ha : sp (gia 4s v 4p cn trng)Lin k t -c h nh th nh gia cp electron t do ca Cl- vi obitan trng lai ha sp caCu+ t o ra phc thu n t c cu h nh thng:

Cl- Cl-

!" !" !" !" !" !" !"3d 4s 4p

[ ] ClCuCl

Phc c s phi tr 4 : Ty thuc t-ng tc phi t v h t trung tm m trng th i lai haca ht tm c khc nhau. Nu phi t vi h t trung tm t-ng tc mnh th ht trung tmlai ha trong dsp2 v phc s c cu h nh vung phng, cn nu t-ng tc y uth ht trungtm lai ha ngoi sp2d v phc s c cu h nh t di n.

V d : Phc [NiCl4]2-Cu h nh ca Ni2+ : 3d8

Trng th i lai ha : sp3 (gia 4s v 4p cn trng)Lin kt -c h nh th nh gia cp electron t do ca Cl- vi obitan trng lai ha sp3 caNi2+ t o ra phc thu n t c cu h nh t di n :

Cl- Cl- Cl- Cl-

!" !" !" ! ! !" !" !" !"3d 4s 4p

Cl

Ni

Cl Cl

Cl

2 -

V d 3: Phc [Cu(CN)4]2-

Cu h nh ca Ni2+ : 3d8

Trng th i lai ha : dsp2 (do CN - l mt phi t tr-ng m nh, t-ng tc ca phi t n yl m cho hai electron d c thn ca Ni2+ b nn l i th nh mt obitan cha electron ghpi to mt obitan d trng)Lin kt -c h nh th nh gia cp electron t do ca CN- vi obitan trng lai ha dsp2ca Ni2+ t o ra phc thu n t c cu h nh vung phng:

CN- CN- CN- CN-

!" !" !" !" !" !" !" !"3d 4s 4p

Ni

CN

CN CN

CN2-

Phc c s phi tr 6 t-ng t nhphc vi s phi tr 4, ty thuc t-ng tc ca phi tv ht trung tm l mnh hay yu m ht trung tm s c lai ha trong d 2sp3 hoc lai hango i sp3d t-ng ng. C hai kiu lai ha ny u t o c u h nh bt di n.

V d 3: Phc [FeF6]4-

Cu h nh ca Ni2+ : 3d6

Trng th i lai ha : sp3d2 (do F - l mt phi t tr-ng y u, t o lai ha ngoi).Lin k t -c h nh th nh gia cp electron t do ca F - vi obitan trng lai hasp3d2 ca Fe2+ t o ra phc thu n t c cu h nh bt din:F- F- F- F- F- F-!" !" !" !" !" !"4s 4p 4d F

Fe

F F

F

F

F

4 -

2. Thuy t tr-ng phi t v phc" Cc lun im ch nh


16/22

Li n k t h a h c


! Lin kt gia phi t v h t trung tm ch l t-ng tc t nh i n! C u h nh electron ca ht trung t m chu nh h-ng ca i n tr-ng to bi c c phi t! i vi h t trung t m l cc nguyn t chuy n ti p :

- Trong phc t di n c c obitan dxy, dyz v dzx h-ng trc tip v o cc phi t, chu t-ngtc t nh i n m nh nn n ng l-ng tng ln so vi cc obitan 2Zd v 22 YXd d n n s

t ch thnh 2 mc n ng l-ng (e v t2) nh- h nh v d-i y :

!!! t2t

!! ed !!!!!

- Trong phc bt din cc obitan 2Zd v 22 YXd h-ng trc tip vo cc phi t, chu

t-ng t c t nh i n m nh nn n ng l-ng tng ln so vi cc obitan dxy, dyz v dzx d n n s tch th nh 2 mc nng l-ng (t2g v eg) nh- h nh v d-i y :

!! ego

!!! t2gd !!!!!

! chnh lch gi-a hai mc n ng l-ng suy bi n -c gi l nng l-ng tch (). ivi mt ht trung tm xc nh, nng l-ng tch ph thuc vo bn cht ca phi t.Gi tr t ng dn (dy ha hc quang ph) ca c c phi t -c x c nh bng thcngi m v cho kt qu sau :I- < Br- < Cl- < SCN- < F- < OH- < H2O< NH3 < NO2

- < CN-...Cc phi t t o ln -c gi l phi t tr-ng mnh (nh- NO2

- , CN -) v c c phi tt o nh -c gi l phi t tr-ng y u (nh- I- , Br- , Cl-).

! i vi c c h t trung t m c s electron d ln hn s obitan suy bin mc th p ( e i

vi phc t din v t2g i vi phc b t di n) th cu h nh electron ph thuc v o c c i l-ng nng l-ng tch v nng l-ng ghpP (nng l-ng ph i tiu tn ghpi electron).- N u < P cc electron sau khi chi m c mc n ng l-ng thp t n s electron tia s tip tc chi m c mc n ng l-ng cao hn tr-c khi b o ha c c obitan.- N u > P c c electron s bo ha mc n ng l-ng th p tr-c khi chi m c mc n ngl-ng cao hn.

" Cc v d :Xt hai phc [Fe(H2O)6]

2+ v [Fe(CN)6]4- c nng l-ng tch t-ng ng l 124,1 kJ/mol v

394,2kJ/mol. i vi Fe2+, P = 210,2kJ/mol. Xc nh c u h nh v t t nh ca hai phc.! i vi phc [Fe(H2O)6]

2+ :

V < P nn ta c cu h nh 242 gget (h nh a)

Phc c 4 electron c th n nn c t nh thun t.

## ego

### t2gd #$####

! i vi phc [Fe(CN)6]4-:

V > P nn ta c cu h nh 62gt (h nh b)

Phc khg c electron c th n nn c t nh nghch t.

eg


17/22

Li n k t h a h c


o#$#$#$ t2g

d #$####

BA I TP LIN KT HO A HOC

1. !"# $ %&'()*+,&%-. +(&/"# 0 1&2"# 3 +&4)5 &(. +(&%(67 +(&869 8&'(: +&%); &461&67 &%) 7 &86 9 8&


18/22

Li n k t h a h c


5. !"# $ %& 8C+,& %() 9 8& WHW8%-@+?& 8C+,& %() 9 8& 8: $ 1& %65 @& 8(@& 869 8& '(: +& %) ; & 461& T%(W@& !"#$%& !'()(*!+,-'",. /'!+0 &>67 &!"#$% & !'*12 -3'",. /'!+0 '4'56U&E&S69 8&6 7 &F\M& E&Z"6; "&%(i 8(& %65 "&46@&XGHM&8@ 9 & %(# 0 &b# $ % &

(*D '&>*9 "&F\ME&&

8. e(W@&'()*+,&'(69 '&!X&%(. &8@9 &%(# 0 &%Cf +&%65 "&869 8&'(: +&%) ; &461&b(C+,&&V&OLl&?&X-Lp&?&RLp&?&GHLM&?&PLl&&>67 &RpL&h&Z"6; "&%(i 8(E&&

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