02 Hoa Hoc Dai Cuong Phan An

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  • 1

    B Y T

    HA I CNG (DNG CHO O TO BC S A KHOA)

    M S: .01.X.06

    NH XUT BN GIO DC H NI 2007

  • 2

    Ch o bin son: V KHOA HC V O TO B Y T

    Ch bin: PGS.TSKH. PHAN AN

    Tham gia bin son: PGS.TSKH. PHAN AN TS. NGUYN S C DS. L HU TR

    Th k bin son: ThS. NGUYN TH NGUYT

    Tham gia t chc bn tho: PH VN THM TS. NGUYN MNH PHA

    Bn quyn thuc B Y t (V Khoa hc v o to) 7702007/CXB/21676/GD M s: 7K720M7 DAI

  • 3

    LI GII THIU Thc hin mt s iu ca Lut Gio dc, B Gio dc v o to v B Y t ban hnh

    chng trnh khung o to bc s a khoa. B Y t t chc bin son ti liu dy hc cc mn c s v chuyn mn theo chng trnh trn nhm tng bc xy dng b sch t chun chuyn mn trong cng tc o to nhn lc y t.

    Sch Ho i cng c bin son da trn chng trnh gio dc ca Trng Trng i hc Y H Ni trn c s chng trnh khung c ph duyt. Sch c PGS.TSKH. Phan An (Ch bin), TS. Nguyn S c v DS. L Hu Tr bin son theo phng chm: Kin thc c bn, h thng; ni dung chnh xc, khoa hc; cp nht cc tin b khoa hc, k thut hin i v thc tin Vit Nam.

    Sch Ho i cng c Hi ng chuyn mn thm nh sch v ti liu dy hc chuyn ngnh bc s a khoa ca B Y t thm nh nm 2007. B Y t quyt nh ban hnh ti liu dy hc t chun chuyn mn ca ngnh trong giai on hin nay. Trong thi gian t 3 n 5 nm, sch phi c chnh l, b sung v cp nht.

    B Y t chn thnh cm n cc tc gi, ThS. Nguyn Th Nguyt v Hi ng chuyn mn thm nh gip hon thnh cun sch; Cm n PGS.TS. ng Vn Tnh, TS. ng Vn Hoi c v phn bin cun sch sm hon thnh kp thi phc v cho cng tc o to nhn lc y t.

    Ln u xut bn, chng ti mong nhn c kin ng gp ca ng nghip, cc bn sinh vin v cc c gi ln xut bn sau sch c hon thin hn.

    V KHOA HC V O TO B Y T

  • 4

    LI NI U Gio trnh Ho hc dng cho sinh vin nm th nht h o to bc s a khoa ca Trng

    i hc Y H Ni c bin son theo khung chng trnh o to bc s a khoa ban hnh theo quyt nh s 12/2001/Q BGD & T ngy 26 thng 4 nm 2001 ca B Gio dc v o to v c thng qua ti Hi ng Chuyn mn Thm nh SGK v TLDH chuyn ngnh BSK (B Y t).

    Gio trnh c in thnh 2 tp: HO I CNG HO V C V HU C

    Vi thi lng 90 tit l thuyt, trong gio trnh ny chng ti ch trnh by nhng kin thc c bn v cn thit sinh vin c th theo hc tip nhng mn hc c s ca Y hc c lin quan n ho hc nh: Ho sinh, Dc l hc, V sinh v Mi trng,...

    Phn c in ch nghing nh l phn m rng thm tham kho. Cui mi bi c cc cu hi t lng gi gip sinh vin vn dng v nm chc c l

    thuyt. Sch do mt s cn b ging dy b mn Ho bin son vi s phn cng nh sau: Phn i cng v V c: PGS. TSKH. Phan An Phn Hu c: TS. Nguyn S c v DS. L Hu TrCh bin: PGS.TSKH. Phan An. Th k ca ban bin son: ThS. Nguyn Th Nguyt Chng ti mong nhn c kin ng gp ca cc bn ng nghip v sinh vin ln ti

    bn sch s hon thin hn.

    Thay mt nhm bin son PGS.TSKH. PHAN AN

  • 5

    Bi 1 CU TO NGUYN T

    MC TIU 1. Phn tch c nhng u im v nhc im ca cc mu nguyn t c in ca Rutherford v Bohr.

    2. Trnh by c nhng lun im c bn ca thuyt c hc lng t trong vic nghin cu nguyn t. 3. M t c nhng c trng ca cc orbital (my electron) nguyn t. 4. Vn dng c nhng quy lut phn b electron trong nguyn t, biu din cu hnh electron ca nguyn t mt nguyn t. 5. M t c cu trc ca bng tun hon cc nguyn t ho hc v quy lut bin thin tnh cht ca cc nguyn t trong bng tun hon.

    M U Khi nim nguyn t " " (khng th phn chia) c cc nh trit hc c Hy

    Lp a ra cch y hn hai ngn nm. Nm1807 Dalton, trn c s cc nh lut c bn ca ho hc, a ra gi thuyt

    nguyn t, tha nhn nguyn t l ht nh nht cu to nn cc cht, khng th chia nhhn bng phng php ho hc.

    Nm 1811 Avogadro, trn c s gi thuyt nguyn t ca Dalton a ra gi thuyt phn t, tha nhn phn t c to thnh t cc nguyn t, l ht nh nht ca mt cht, mang y tnh cht ca cht .

    Nm 1861 thuyt nguyn t, phn t chnh thc c tha nhn trong hi ngh ho hc th gii hp ti Thu S.

    Ch n cui th k XIX v u th k XX vi nhng thnh tu ca vt l, cc thnh phn cu to nn nguyn t ln lt c pht hin.

    1. THNH PHN CU TO CA NGUYN T V mt vt l, nguyn t khng phi l ht nh nht m c cu to phc tp, gm t nht l

    ht nhn v cc electron. Trong ht nhn nguyn t c hai ht c bn: proton v ntron.

    Ht Khi lng (g) in tch (culong) electron (e) 9,1.1028 1,6.1019

    proton(p) 1,673.1024 +1,6.1019

    ntron(n) 1,675.1024 0

  • 6

    Khi lng ca khi lng p. in tch ca e l in tch nh nht v c ly lm n v in tch, ta ni electron mang

    1v in tch m (e) cn proton mang 1v in tch dng (+e). Nu trong ht nhn nguyn t ca mt nguyn t no c Z proton th in tch ht nhn

    l +Ze v nguyn t phi c Z electron, v nguyn t trung ho in. Trong bng tun hon, s th t ca cc nguyn t cng l s ch in tch ht nhn hay s

    proton trong ht nhn nguyn t ca nguyn t . 2. NHNG MU NGUYN T C IN 2.1. Mu Rutherford (Rzfo Anh) 1911

    T th nghim bn cc ht qua mt l vng mng, Rutherford a ra mu nguyn thnh tinh (hnh 1.1).

    Nguyn t gm mt ht nhn gia v cc electron quay xung quanh ging nh cc hnh tinh quay xung quanh mt tri.

    Ht nhn mang in tch dng, c kch thc rt nh so vi kch thc ca nguyn tnhng li tp trung hu nh ton b khi lng nguyn t.

    Mu Rutherford gii thch c kt qu th nghim trn v cho php hnh dung mt cch n gin cu to nguyn t. Tuy nhin khng gii thch c s tn ti ca nguyn t v hin tng quang ph vch ca nguyn t.

    Hnh 1.1. S th nghim ca Rutherford v mu nguyn t hnh tinh

    2.2. Mu Bohr (Bo an Mch) 1913 Da trn thuyt lng t ca Planck (Plng) Bohr a ra hai nh : Trong nguyn t electron ch c th quay trn nhng qu o xc nh gi l cc qu o

    lng t, mi qu o ng vi mt mc nng lng xc nh. Qu o lng t phi tho mn iu kin sau:

    (1.1)

  • 7

    h: hng s Planck 6,62.1027 erg.s m: khi lng electron v: tc chuyn ng ca electron r: bn knh qu o n: s nguyn t 1, 2, 3... n c gi l s lng t

    Tch mvr gi l momen ng lng Khi quay trn nhng qu o lng t electron khng pht hay thu nng lng. N ch

    pht hay thu nng lng khi chuyn t mt qu o ny sang mt qu o khc.

    Hnh 1.2. Cc qu o lng t theo thuyt nguyn t ca Bohr v s to thnh cc dy quang ph vch ca nguyn t hydro

    Da vo nhng nh lut ca c hc c in Bohr tnh c bn knh rn ca cc qu o electron trong nguyn t hydro v gi tr nng lng En ca electron tng ng trn cc qu o :

    (1.2)

    e: gi tr tuyt i ca in tch electron Electron chuyn ng c trn qu o nh s cn bng gia lc ly tm v lc ht culong:

    hay mv2r = e2

    Kt hp vi iu kin qu o Bohr (1.1) ta c biu thc tnh rn (1.2)

  • 8

    Nu thay cc gi tr ca hng s (H n v CGS): h = 6,62.1027 ec.s

    m = 9,1.1028 g

    e = 4,8.1010 vt vo phng trnh (1.2) ta c:

    rn = n2.0,53. 108 cm = n2. 0,53. (1 = 108 cm)

    T : r1 = 12. 0,53 = 0,53 r2 = 22. 0,53 = 4r1

    r3 = 32. 0,53 = 9r1

    ....

    rn = n2. 0,53 = n2 r1

    (1.3)

    Nng lng ton phn ca electron bng tng ng nng v th nng:

    thay mv2 bng ta c:

    Thay gi tr ca r t (1.2) ta c (1.3) Nu thay cc gi tr ca hng s vo (1.3) ta c:

  • 9

    T cc cng thc (1.2) v (1.3) ta thy s n lm gin on (nh ngi ta ni n lng tho) bn knh qu o electron v nng lng ca electron trong nguyn t. V vy n c gi l s lng t.

    Thuyt Bohr cho php gii thch cu to quang ph vch ca nguyn t hydro v tnh c bn knh ca nguyn t hydro trng thi c bn.

    Bnh thng nguyn t trng thi c nng lng thp nht (trng thi c bn). Khi b kch thch cc electron chuyn t trng thi c bn (qu o gn nhn nht) sang trng thi c nng lng cao (qu o xa nhn hn). Trng thi kch thch l trng thi khng bn nn ngay lp tc electron li tr v trng thi c bn (c th qua mt s trng thi trung gian). Mi bc nhy pht ra mt lng t tng ng vi mt vch trn quang ph ca nguyn t.

    Tuy nhin thuyt Bohr khng gii thch c quang ph ca cc nguyn t phc tp cng nh s tch vch quang ph di tc dng ca t trng. iu cho thy rng i vi nhng ht hay h ht vi m nh electron, nguyn t th khng th p dng nhng nh lut ca c hc c in. Cc h ny c nhng c tnh khc vi h v m v phi c nghin cu bng c hc lng t. 3. NHNG TIN CA C HC LNG T 3.1. Thuyt lng t Planck (Plng c) 1900

    nh sng hay bc x ni chung khng phi l lin tc m gm nhng lng nh ring bit gi l nhng lng t.

    Mi lng t mang mt nng lng tnh bng biu thc: E = h (1.4) : tn s ca bc x. 3.2. Thuyt sng ht ca nh sng

    Thuyt sng v nh sng c Maxwell (Macxuen) a ra nm 1865 gii thch c hin tng nhiu x, giao thoa ca nh sng nhng khng gii thch c hiu ng quang in.

    Theo thuyt lng t th nh sng gm nhng lng t nng lng E = h pht i t ngun sng. Mt khc theo h thc tng i Einstein (Anhxtanh) E = mc2 th mt vt th bt k nu

    mang nng lng E s c khi lng . Nh vy nh sng c tnh cht ht. Ngy nay ngi ta tha nhn bn cht sng ht ca nh sng. T h thc Einstein v thuyt lng t ta c:

    mc2 = h

    t : (1.5)

  • 10

    3.3. Tnh cht sng ht ca ht vi m (electron, nguyn t, phn t...) Nm 1924 De Broglie ( Bri Php) trn c s thuyt sng ht ca nh sng ra

    thuyt sng ht ca vt cht: Mi ht vt cht chuyn ng u lin kt vi mt sng gi l sng vt cht hay sng lin

    kt, c bc sng tnh theo h thc:

    (1.6)

    m: khi lng ca ht v: tc chuyn ng ca ht

    Nm 1927 Davisson v Germer lm thc nghim cho thy hin tng nhiu x chm electron. Nh vy bn cht sng ca electron cng c tha nhn.

    Nm 1924 ngi ta xc nh c khi lng ca electron ngha l tha nhn electron c bn cht ht.

    V d: Electron khi lng 9,1.10-28g chuyn ng vi vn tc 108 cm/s s c mt sng lin kt

    vi tnh theo biu thc (1.6)

    Nh vy: electron va c bn cht sng va c bn cht ht. i vi nhng vt th v m, m c gi tr rt ln so vi hng s h nn c gi tr rt nh, v

    vy c th b qua bn cht sng. V d: Mt t c khi lng 1000 kg chuyn ng vi tc 72 km/h s c mt sng lin kt

    bc sng ny l v cng nh v vy thc t c th b qua. 3.4. Nguyn l bt nh Heisenberg (Haixenbec c) 1927

    i vi ht vi m khng th xc nh chnh xc ng thi c tc v v tr

    (1.7)

    x: bt nh v v tr

  • 11

    v: bt nh v tc m: khi lng ht

    Theo h thc ny th vic xc nh to cng chnh xc bao nhiu th xc nh tc cng km chnh xc by nhiu.

    V d: Nu ly bt nh ca php o v tr electron trong nguyn t x l 1010 cm (nguyn t c

    ng knh c 10 8 cm) th bt nh trong php o tc s l:

    ngha l gp mt sai s xp x bng tc ca nh sng. 4. KHI NIM C BN V C HC LNG T 4.1. Hm sng

    Trng thi ca mt h v m s hon ton c xc nh nu bit qu o v tc chuyn ng ca n. Trong khi i vi nhng h vi m, do bn cht sng ht v nguyn l bt nh, khi nim qu o khng cn ngha na.

    Trong c hc lng t mi trng thi ca mt ht hay h ht vi m c m t bng mt hm xc nh gi l hm sng hay hm trng thi (x, y, z) (c l: pxi) ca cc bin s x, y, z trong to Decard hay (r, , ) ca cc bin s r, , trong to cu.

    Bn thn hm sng khng c ngha vt l g nhng 2 li c ngha vt l rt quan trng.

    2 biu th mt xc sut tm thy ht ti mt im nht nh trong khng gian. 2 dv biu th xc sut tm thy ht ti mt th tch nguyn t dv. ng vi ngha vt l ca 2, hm sng phi tho mn mt s iu kin nh: n tr, lin

    tc, gii ni v phi c chun ho. Hm phi n tr ngha l ch c mt gi tr ti mt im xc nh, cng chnh l n xc

    nh mt cch n gi xc sut tm thy ht ti mt im nht nh. Hm phi lin tc v gii ni ngha l n phi tin dn n 0 khi r tin dn n v cng. Hm phi c chun ho. V mt ton hc iu kin ny c th hin phng trnh:

    c ngha l xc sut tm thy ht trong ton b khng gian l 1. Hm sng nhn c khi gii phng trnh sng.

  • 12

    4.2. Phng trnh sng C s ca c hc lng t l phng trnh sng do nh bc hc o Schrodinger (Sring)

    a ra nm 1926. l phng trnh m t trng thi chuyn ng ca ht vi m trong khng gian.

    Phng trnh c dng nh sau:

    (1.8)

    U: th nng ca ht E: nng lng ton phn ca ht m: khi lng ca ht

    Phng trnh Schrodinger thng c vit dng rt gn:

    (1.9)

    gi l ton t Laplas i vi mt bi ton c th, thay U bng biu thc tnh th nng ca ht v gii phng

    trnh ta nhn c cc nghim 1, 2, 3... n c trng cho cc trng thi khc nhau ca ht vi m v cc gi tr nng lng ng vi mi trng thi . 5. NGUYN T HYDRO V NHNG ION GING HYDRO

    Nguyn t hydro l nguyn t n gin nht. N ch gm mt electron chuyn ng trong trng th ca ht nhn mang in tch +1. Cc ht He+, Li2+ cng l nhng h gn ging nguyn t hydro, ch c mt electron. V vy phng trnh Schrodinger cho cc trng hp ny c thgii c chnh xc. Nhng kt qu thu c t vic gii bi ton i vi nguyn t hydro l cs cho h thng l thuyt v cu to nguyn t. 5.1. Phng trnh Schrodinger i vi nguyn t hydro

    Nguyn t hydro gm ht nhn mang in tch + e v mt electron mang in tch e. Do tng tc tnh in vi proton, electron c mt th nng U = e2/r. T phng trnh Schrodinger cho bi ton nguyn t hydro c dng:

    (1.10)

    r: khong cch t electron n ht nhn i vi trng hp He+ v Li2+ biu thc th nng s l:

  • 13

    Ze2/r Z l in tch nhn V trng th c i xng cu nn thun tin cho vic tnh ton ngi ta s dng to

    cu. Khi hm l hm ca cc bin s r, , . Gii phng trnh (1.10) ngi ta c cc hm (r, , ), t tm c 2 (r, , ) biu

    th xc sut tm thy electron ti nhng im khc nhau trong khng gian nguyn t, nng lng ton phn E, mmen ng lng M, hnh chiu ca mmen ng lng Mz ca electron tng ng vi cc hm . Trong biu thc tnh cc i lng ny xut hin nhng con s nguyn n, l, m tng ng c gi l cc s lng t. 5.2. Orbital nguyn t. My electron

    Phng trnh Schrodinger c v s nghim. l nhng hm (r, , ), c gi l cc orbital nguyn t (atomic orbital) vit tt l AO. Nh vy: Orbital nguyn t l nhng hm sng m t cc trng thi ca electron trong nguyn t.

    Mi hm sng l tch ca hai phn: Rnl (r) gi l phn bn knh v ph thuc vo khong cch r; Ylm (, ) gi l phn gc ph thuc cc gc , . nlm (r, , ) = Rnl (r). Ylm (, ) (1.11)

    BNG 1.1. MT S ORBITAL CHNH CA NGUYN T HYDRO

    V d: Nghim n gin nht m t trng thi c bn ca electron (trng thi e c nng lng thp

    nht) trong nguyn t hydro c dng:

  • 14

    Hm ny ch ph thuc vo bin s to r. T hm ny ta bit c 2 (r) biu th mt xc sut c mt electron ti v tr tng ng.

    Biu din s ph thuc ca hm 2 theo khong cch r ta c ng cong phn b mt xc sut c mt electron trng thi c bn (hnh 1.3). Theo :

    Mt xc sut c mt electron gim dn t ht nhn ra ngoi. khong cch xa ht nhn 2 c gi tr nh nhng khng bng 0. (ng biu din khng

    ct trc honh m ch tim cn vi trc ny). Mt cch hnh nh ngi ta cng c th biu din s phn b mt xc sut tm thy

    electron trong nguyn t bng nhng du chm. Mt ca cc chm s ln gn nhn v tha dn khi cng xa nhn. Khi orbital nguyn t ging nh mt m my electron. d hnh dung ngi ta thng coi:

    My electron l vng khng gian xung quanh ht nhn trong tp trung phn ln xc sut c mt electron (khong 90 95% xc sut).

    Nh vy my electron c th coi l hnh nh khng gian ca orbital nguyn t

    Hnh 1.3. My 1s (a) v 2s (b)

    5.3. Cc s lng t Nh ni trn cc s lng t xut hin trong qu trnh gii phng trnh Schrodinger

    tm mt s i lng c trng cho mt AO. Nh vy l mi hm sng (hay mi AO) c c trng (c xc nh) bi 4 tham s n,

    l, m, ms gi l cc s lng t. 5.3.1. S lng t chnh n

    n nhn cc gi tr t 1, 2, 3.... n. n xc nh nng lng ca electron trong nguyn t theo biu thc:

  • 15

    Cc AO c cng n s c cng mt mc nng lng v to ra mt lp orbital nguyn t. n 1 2 3 4... n

    K hiu lp K L M N... Mc nng lng E1 E2 E3 E4. .... En

    5.3.2. S lng t ph l Cc gi tr ca l ph thuc vo s lng t chnh: l = 0, 1, 2... (n 1) l xc nh momen ng lng ca electron trong biu thc:

    (1.12)

    ng vi mt gi tr ca n (mt lp) c n gi tr ca l (n phn lp) Lp n K n = 1 l = 0

    L n = 2 l = 0 l = 1

    M n = 3 l = 0 l = 1 l = 2

    N n = 4 l = 0 l = 1 l = 2 l = 3

    K hiu phn lp s p d f Mun ch ra mt phn lp thuc lp no ngi ta vit s th t lp trc k hiu phn lp.

    V d: 2s ch electron (hayAO) thuc phn lp s (l = 0) ca lp 2 (n = 2). 3d........................................................d (l = 2).............3 (n = 3).

    5.3.3. S lng t t m m nhn cc gi tr t l n + l k c s 0. Nh vy ng vi mt gi tr ca l c 2l + 1 gi

    tr ca m. m xc nh hnh chiu ca momen ng lng Mz ca electron trn mt phng z ca

    trng ngoi, trong biu thc:

  • 16

    (1.13)

    Nh vy cc AO c Mz khc nhau (c m khc nhau) s nh hng khc nhau trong khng gian, m quyt nh hng ca AO hay hng ca my electron.

    Phn lp s l = 0 m = 0 ch c mt cch nh hng. Phn lp p l = 1 m = 1, 0, +1 c 3 cch nh hng tng ng:

    px, pz, py

    Phn lp d l = 2 m = 1, 2, 0, +1, +2 c 5 cch nh hng tng ng:

    5.3.4. S lng t spin mS Nghin cu quang ph ca cc nguyn t ngi ta thy cn gi thit thm rng electron

    ngoi chuyn ng quanh nhn cn t quay quanh trc ring ca n. Chuyn ng ny c gi l spin v c c trng bng s lng t spin ms. ms ch c hai gi tr l: .

    Nh vy trng thi ca mi electron trong nguyn t c c trng bi bn s lng t n, l, m, ms: c gi l orbital ton phn

    n l m c gi l orbital khng gian. BNG 1.2. TRNG THI LNG T CA ELECTRON THUC BA LP U

    n l m AO S AO S e

    100 1 0 0 1s 1 2

    200 0 0 2s 1 2

    211 2 1 2px

    210 1 0 2pz 3 6

    21+1 +1 2py

    300 0 0 3s 1 2

    311 1 3px

    310 1 0 3pz 3 6

    31+1 3 +1 3py 322 2 3dxy

    321 1 3dyz

  • 17

    320 2 0 5 10

    32+1 +1

    32+2 +2 3dzx

    5.4. Hnh dng v du ca cc orbital (cc my electron) Nh bit hm sng m t trng thi ca mt electron c dng:

    nlm (r,,) = Rnl (r). Ylm (, ) R(r) l phn bn knh, quyt nh kch thc ca AO. Y(, ) l phn gc, quyt nh hnh dng ca AO.

    Nu biu din s ph thuc ca phn gc ca hm sng vo cc gc , khi r khng i, (r c trn nh th no b mt gii hn thu c bao chm mt khng gian trong xc sut c mt electron chim 90 95%) th cc b mt gii hn ny cho ta hnh dng ca cc orbital hay cc my electron (hnh 1.4).

    Mt khc v orbital l mt hm (x, y, z) hay (r, , ) m cc bin s l cc to khng gian, nn tu theo cc tr ca bin m hm c th c gi tr dng hay m. Ngi ta thng ghi du + hoc trn mt gii hn biu din hnh dng cc orbital.

    Orbital s c dng hnh cu. Cc orbital px, py, pz c hnh s 8 ni hng theo 3 trc to ox, oy, oz. Cc orbital dxy, dyz, dzx u c dng hnh hoa th (4 cnh) hng theo ng phn gic ca

    cc gc tng ng xoy, yoz, zox.

    Orbital c dng hoa th nhng hng theo 2 trc ox v oy.

    Ring orbital gm hnh s 8 ni hng theo trc oz v mt vnh khn nm trn mt phng xoy. Di y l hnh dng ca mt s AO v du ca n:

  • 18

    Hnh 1.4. Hnh dng v s sp xp trong khng gian ca mt s orbital nguyn t

    6. NGUYN T NHIU ELECTRON 6.1. M hnh v cc ht c lp hay m hnh dng hydro

    Khc vi nguyn t hydro, trong nguyn t nhiu electron ngoi nhng tng tc gia cc electron v ht nhn cn c nhng tng tc gia cc electron vi nhau. Trong trng hp ny phng trnh Schrodinger cha qu nhiu bin s nn khng gii c chnh xc. V vy ngi ta phi s dng mt phng php gii gn ng da trn mt m hnh gn ng thch hp gi l m hnh v cc ht c lp.

    Trong nguyn t nhiu electron, mi electron chuyn ng c lp vi cc electron khc trong mt trng trung bnh c i xng cu to bi ht nhn v cc electron khc.

    Trn c s ngi ta xt ring tng electron, c gi l trng thi n electron. Nh vy, bi ton N electron chuyn thnh N bi ton n electron ging nh trng hp nguyn thydro. Ngha l cc orbital trong nguyn t nhiu electron cng c c trng bng cc slng t n, l, m, ms v c hnh dng tng t nh nguyn t H, ch khc v kch thc v nng lng.

  • 19

    6.2. Quy lut phn b cc electron trong nguyn t 6.2.1. Nguyn l ngn cm Pauli (PaoliThy S). S electron ti a mi lp

    Trong nguyn t khng th c hai electron ging nhau c bn s lng t. iu ny cng c ngha l trong mt nguyn t nu hai electron c m t bng hm sng

    nlm c cc s lng t n, l, m ging nhau th chng phi c spin khc nhau, s lng t th tphi khc nhau.

    V s lng t spin ch c hai gi tr nn theo nguyn l Pauli iu cng c ngha l trong mi AO ch c th c ti a hai electron. T ta c th tnh c s electron ti a trong mi phn lp (phn mc), trong mi lp.

    ng vi mt gi tr ca n c n gi tr ca l. ng vi mt gi tr ca l c (2l + 1) gi tr ca m.

    V ms ch c hai gi tr nn phn mc l ch c nhiu nht 2(2l + 1) electron v tng s electron ca mt mc (hay lp) s l:

    (1.14)

    V d: Phn mc s (l = 0) c 1 AO (s), ti a c 2 electron Phn mc p (l = 1) c 3 AO (px, py, pz) ti a c 6 electron Phn mc d (l = 2) c 5 AO, ti a c 10 electron Phn mc f (l = 3) c 7 AO, ti a c 14 electron mc n = 1 c 2 electron mc n = 2 c 8 electron (2e phn mc s + 6e phn mc p) mc n = 3 c 18 electron (2e ...s + 6e ...p + 10e ... d) mc n = 4 c 32 electron (2e s + 6e p + 10e d +14e f)

    6.2.2. Nguyn l vng bn. Cu hnh electron ca nguyn t Trong nguyn t cc electron chim ln lt cc orbital c nng lng t thp n cao. Bng phng php quang ph nghim v tnh ton l thuyt ngi ta xc nh c th

    t tng dn nng lng ca cc AO theo dy sau y: 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f 6d 7p...

  • 20

    nh c th t bc thang nng lng ny ta dng s sau:

    Dy nng lng ny tun theo mt quy tc sau y gi l quy tc Kleskovxky: Mc nng lng ca AO tng dn theo tr s (n+l)

    V d: 3s (3 + 0) 3p (3 +1); 4s (4 + 0) 3d (3 + 2) Hai AO c (n+l) bng nhau th AO no c n ln hn s c nng lng cao hn.

    V d: 4p (4 + 1) 5s (5 + 0); 4d (4 + 2) 5p (5 + 1) Da vo nguyn l Pauli v nguyn l vng bn ngi ta c th biu din nguyn t ca mt

    nguyn t bng cu hnh electron. c cu hnh electron ca mt nguyn t, trc ht ta in dn cc electron vo bc thang

    nng lng ca cc AO. Sau sp xp li theo tng lp AO. V d:

    He (z = 2) 1s2

    Li (z = 3) 1s2 2s1

    Cl (z = 17) 1s2 2s2 2p6 3s2 3p5

    Sc (z = 21) 1s2 2s2 2p6 3s2 3p6 3d1 4s2

    Ch : c mt s ngoi l:

  • 21

    Cu (z = 29) 1s2 2s2 2p6 3s2 3p6

    Cr (z = 24) 1s2 2s2 2p6 3s2 3p6

    Cu hnh (trng thi vi bo ho) bn hn cu hnh Cc nguyn t Ag (z = 47) v Au (z = 79) cng c cu hnh tng t Cu

    Cu hnh (trng thi vi na bo ho) bn hn cu hnh Nguyn t Mo (z = 42) c cu hnh tng t Cr

    6.2.3. Quy tc Hund (Hun c). Cu hnh electron dng lng t Ngoi cch biu din cc AO di dng cng thc nh trn, ngi ta cn biu din mi AO

    bng mt vung gi l lng t. Cc AO ca cng mt phn mc c biu din bng nhng vung lin nhau. V d:

    Trong mi lng t ch c th c 2 electron c spin ngc nhau c biu din bng 2 mi tn ngc nhau

    Trn c s thc nghim Hund a ra mt quy tc phn b cc electron vo cc lng tnh sau:

    Trong mt phn mc cc electron c xu hng phn b u vo cc lng t sao cho selectron c thn l ln nht. V d:

    Thng thng ch cn vit cu hnh electron i vi cc phn mc lp ngoi cng v phn mc d hoc f lp st ngoi cng m cha bo ho.

    Cn lu rng cu hnh ni trn l i vi cc nguyn t trng thi c bn. Khi b kch thch electron c th nhy ln nhng phn mc cao hn trong cng mt mc nng lng. V d:

  • 22

    Nh vy trng thi c bn C c hai electron c thn cn trng thi kch thch (c k hiu l C*) C* c bn electron c thn. Chnh cc electron c thn ny l cc electron ho tr. 7. H THNG TUN HON CC NGUYN T HO HC 7.1. nh lut tun hon Mendeleev (Menlep Nga) 1869

    Tnh cht ca cc nguyn t, thnh phn v tnh cht ca cc hp cht to nn t cc nguyn t bin thin tun hon theo chiu tng ca khi lng nguyn t.

    Ngy nay nh lut tun hon c pht biu chnh xc hn bng cch thay cm t khi lng nguyn t bng cm t in tch ht nhn.

    Trn c s nh lut tun hon, Mendeleev sp xp mt cch c h thng cc nguyn tthnh mt bng gm nhng hng v ct gi l bng tun hon (BTH) cc nguyn t ho hc. 7.2. BTH cc nguyn t ho hc 7.2.1. Nguyn tc sp xp cc nguyn t trong BTH

    Cc nguyn t c sp xp theo th t tng dn ca in tch ht nhn. S in tch ht nhn trng vi s th t ca nguyn t.

    Cc nguyn t c tnh cht ho hc ging nhau c xp trong cng mt ct. Mi hng (bng di) c gi l mt chu k. Mi chu k c bt u bng mt kim loi

    kim, (tr chu k 1, bt u bng hydro) v c kt thc bng mt kh him. 7.2.2. Cu trc ca BTH

    BTH gm 7 chu k: Chu k 1 c 2 nguyn t Chu k 2 v 3, mi chu k c 8 nguyn t Chu k 4 v 5, mi chu k c 18 nguyn t Chu k 6 c 32 nguyn t Chu k 7 c 24 nguyn t (cha hon thnh) 14 nguyn t ng sau lantan thuc chu k 6 gi l cc lantanit. 14 nguyn t ng sau actini thuc chu k 7 gi l cc actinit. Cc lantanit v actinit xp ra ngoi bng thnh hai hng, mi hng 14 nguyn t. Tr cc nguyn t c xp ra ngoi bng, mi chu k di (tr chu k 7) c 18 nguyn t

    xp thnh 18 ct.

  • 23

    Cc nguyn t thuc cc ct 1, 2 v cc ct t 13 n 18 to thnh 8 nhm nh s t IA n VIIIA c gi l cc nhm chnh hay cc nhm A.

    10 ct cn li to thnh 8 nhm ph (nhm B) nh s theo th t IIIB... VIIIB v sau l IB v IIB. Mi ct to thnh mt nhm, ring nhm VIIIB gm 3 ct.

    BNG 1.3. CU HNH ELECTRON CA MT S NGUYN T

    Chu k

    z Nguyn t

    Cu hnh electron Chu k

    z Nguyn t

    Cu hnh electron

  • 24

    1 1 H 1s1 55 Cs [Xe] 6s1

    2 He 1s2 56 Ba 6s2

    3 Li [He] 2s1 57 La 5d1 6s2

    4 Be 2s2 58 Ce 4f2 5d0 6s2

    2 5 B 2s2 2p1 59 Pr 4f3 5d0 6s2

    ... ... .... 6 ... ... ....

    10 Ne 2s2 2p6 63 Eu 4f7 5d0 6s2

    11 Na [Ne] 3s1 64 Gd 4f7 5d1 6s2

    12 Mg 3s2 ... ... ....

    3 13 Al 3s2 3p1 71 Lu 4f14 5d1 6s2

    ... ... .... 72 Hf 5d2 6s2

    18 Ar 3s2 3p6 ... ... ....

    19 K [Ar] 4s1 80 Hg 5d10 6s2

    20 Ca 4s2 81 Tl 6s2 6p1

    21 Sc 3d1 4s2 ... ... ....

    4 ... ... .... 86 Rn 6s2 6p6

    30 Zn 3d10 4s2 87 Fr [Rn] 7s1

    31 Ga 3d10 4s2 4p1 88 Ra 7s2

    ... ... .... 89 Ac 6d1 7s2

    36 Kr 3d10 4s2 4p6 90 Th 6d2 7s2

    37 Rb [Kr] 5s1 7 91 Pa 5f2 6d1 7s2

    38 Sr 5s2 ... ....

    39 Y 4d1 5s2 93 Np 5f4 6d1 7s2

    ... ... .... ... ....

    5 48 Cd 4d10 5s2 96 Cm 5f7 6d1 7s2

    49 In 4d10 5s2 5p1 97 Bk 5f9 6d0 7s2

    ... ... .... ... ... ....

    54 Xe 4d10 5s2 5p6 103 Lr 5f14 6d1 7s2

    104 Ku 6d2 7s2

  • 25

    7.3. Cu hnh electron ca cc nguyn t trong BTH Chu k 1: Gm 2 nguyn t, c mt lp electron, cc electron ln lt in vo 1s. Ngi ta

    gi cc nguyn t ny l nguyn t s. Chu k 2: Gm 8 nguyn t, c hai lp electron. Lp trong c cu hnh electron ca He. Hai

    nguyn t u l cc nguyn t s (2s). Cc nguyn t tip theo, s electron c in vo hai phn lp 2s v 2p, trong phn lp 2s bo ho, cn phn lp 2p c s electron tng dn t2p1 n 2p6. Cc nguyn t ny gi l cc nguyn t p.

    Chu k 3: Gm 8 nguyn t, c ba lp electron. Cc lp trong c cu hnh electron ca Ne. Hai nguyn t u l cc nguyn t s (3s). Su nguyn t tip theo l cc nguyn t p (3p1 3p6).

    Chu k 4: Gm 18 nguyn t, c bn lp electron. Cc lp trong c cu hnh electron ca Ar. Hai nguyn t u l cc nguyn t s (4s). Mi nguyn t tip theo, cc electron c in vo hai phn lp 3d v 4s, trong phn lp 4s bo ho, cn phn lp 3d c s electron tng dn t 3d1 n 3d10. Cc nguyn t ny gi l cc nguyn t d hay cc nguyn t chuyn tip. Cui cng l su nguyn t p (4p1 4p6).

    Chu k 5: Gm 18 nguyn t, c nm lp electron. Cc lp trong c cu hnh electron ca Kr. Hai nguyn t u l cc nguyn t s (5s). Tip theo l mi nguyn t d (4d1 4d10). Su nguyn t cui cng l cc nguyn t p (5p1 5p6).

    Chu k 6: Gm 32 nguyn t. Ngoi cc nguyn t s, p, d nh chu k 5 cn thm 14 nguyn t f. Cc nguyn t f ny c hai lp electron ngoi cng ging nhau 5d1 6s2 nhng phn lp 4f c s electron ln lt t 4f1 n 4f14.

    Chu k 7: Chu k cha kt thc, tuy nhin theo quy lut ngi ta d on phi gm 32 nguyn t. Vi cc nguyn t hin bit, cu hnh electron c s lp li tng t nh cc nguyn t chu k 6.

    Nhn xt: Chu k 1, 2, 3 l cc chu k nh ch gm cc nguyn t s v p. Cc nguyn t ny c

    xp vo cc nhm chnh (nhm A) ca BTH. Tng s electron thuc lp ngoi cng (s + p) bng ch s ca nhm. S lp electron bng ch s chu k.

    Nhm IA IIA IIIA IVA VA VIA VIIA VIIIA

    Cu hnh e s1 s2 s2p1 s2p2 s2p3 s2p4 s2p5 s2p6

    Chu k 4, 5 l cc chu k ln ngoi cc nguyn t s v p vi cu hnh electron tng tnh cc nguyn t thuc chu k nh, cn c thm 10 nguyn t d. Cc nguyn t ny c xp vo cc nhm ph (nhm B) ca BTH.

    Nhm IB IIB IIIB IVB VB VIB VIIB VIIIB

    Cu hnh e d10s1 d10s2 d1s2 d2s2 d3s2 d5s1 d5s2 d6 d7 d8s2

    Chu k 6, 7 l cc chu k ln, ngoi cc nguyn t s, p v d tng t nh cc nguyn tthuc chu k 4, 5 cn c thm 14 nguyn t f c xp thnh hai hng di BTH.

  • 26

    Bit s th t ca mt nguyn t ngi ta c th bit c cu hnh electron ca n. T suy ra c v tr ca nguyn t trong BTH. V d:

    Bit s th t ca nguyn t ln lt l z = 9, 11, 18, 25, 34. Ta c cu hnh electron nhsau:

    7.4. Bin thin tun hon mt s tnh cht ca cc nguyn t S lp li tun hon cu hnh electron ca nguyn t theo chiu tng ca in tch ht nhn

    chnh l nguyn nhn ca s lp li tun hon cc tnh cht ca nguyn t. 7.4.1. Bin thin tnh cht trong mt chu k

    Khi i t u n cui chu k, in tch ht nhn tng ng thi bn knh li gim i. Kt qu l lm tng lc ht gia ht nhn v electron lp ngoi cng, c ngha l lm gim tnh khv tng tnh oxy ho.

    Cc kh him c cu hnh bo ho (ns2 np6) nn rt bn vng, khng cho v cng khng thu thm electron nn hu nh khng tham gia vo phn ng ho hc. Nh vy mi chu k (tr chu k 1) c bt u bng mt kim loi kim v kt thc bng mt kh him.

    Tc bin thin tnh cht ca cc nguyn t cc chu k nh rt nhanh. Trong khi cc chu k ln chm hn nhiu, chu k cng ln tc bin thin cng chm. V d chu k 2 ch ba nguyn t u (Li, Be, B) chuyn t mt kim loi mnh (Li) sang mt phi kim. Nhng chu k 4, t K u chu k n Ga (qua 11 nguyn t) vn l mt kim loi.

    BNG 1.4. BN KNH NGUYN T CA MT S NGUYN T ()

    IA IIA IIIA IVA VA VIA VIIA VIIIA

    H

    0,37

    He

    1,22

    Li

    1,52

    Be

    1,13

    B

    0,88

    C

    0,77

    N

    0,70

    O

    0,66

    F

    0,64

    Ne

    1,60

    Na

    1,86

    Mg

    1,60

    Al

    1,43

    Si

    1,17

    P

    1,70

    S

    1,04

    Cl

    0,99

    Ar

    1,91

    K

    2,31

    Ca

    1,97

    Ga

    1,22

    Ge

    1,22

    As

    1,21

    Se

    1,17

    Br

    1,14

    Kr

    2,01

  • 27

    Rb

    2,44

    Sr

    2,15

    In

    1,62

    Sn

    1,40

    Sb

    1,41

    Te

    1,37

    I

    1,33

    Xe

    2,20

    Cs

    2,62

    Ba

    1,17

    Tl

    1,71

    Pb

    1,75

    Bi

    1,46

    Po

    1,40

    At

    1,40

    Rn

    Fr

    2,70

    Ra

    2,20

    7.4.2. Bin thin tnh cht trong mt phn nhm chnh Trong mt phn nhm chnh, theo chiu t trn xung di, tnh kh tng dn v tnh oxy

    ho gim dn. l v, i t trn xung, bn knh nguyn t tng dn (tng s lp electron), in tch ht nhn cng tng, nhng bn knh tng nhiu, nh hng ln n lc ht gia ht nhn v electron ngoi cng.

    7.4.3. Bin thin tnh cht trong mt phn nhm ph Tnh cht ho hc ca cc nguyn t gia cc phn nhm chnh rt khc nhau. T kim loi

    in hnh n phi kim, kh him. Cn cc nguyn t thuc phn nhm ph d cho c tnh cht khc nhau cng u l kim loi. iu cho thy s bin thin tnh cht cc nguyn t thuc phn nhm ny (nguyn t d v f) l rt chm chp.

    Cc nguyn t d thuc cng mt phn nhm ph c phn lp d st lp ngoi cng v lp ngoi cng ging nhau. Chng ch khc nhau v bn knh nguyn t v in tch ht nhn. Theo chiu t trn xung, in tch ht nhn tng nhiu nhng bn knh nguyn t tng khng ng k, dn n tng lc ht ca ht nhn i vi electron lp ngoi cng. Do tnh kim loi gim. V d:

    Phn nhm IB Phn nhm IIB Cu Zn Ag Cd Au Hg

    Trong nhm IB Cu l kim loi tng i hot ng nhng Au l kim loi tr. Trong nhm IIB cng tng t: Zn c tnh kh mnh, Hg c tnh kh yu, ng sau H trong

    dy hot ng ca kim loi. BNG 1.5. CU HNH ELECTRON LP NGOI CNG CA CC NGUYN T NHM A

    IA IIA IIIA IVA VA VIA VIIA VIIIA

    H

    1s1

    He

    1s2

  • 28

    Li

    2s1

    Be

    2s2

    B

    2s22p1

    C

    2s22p2

    N

    2s22p3

    O

    2s22p4

    F

    2s22p5

    Ne

    2s22p6

    Na

    3s1

    Mg

    3s2

    Al

    3s23p1

    Si

    3s23p2

    P

    3s23p3

    S

    3s23p4

    Cl

    3s23p5

    Ar

    3s23p6

    K

    4s1

    Ca

    4s2

    Ga

    4s24p1

    Ge

    4s24p2

    As

    4s24p3

    Se

    4s24p4

    Br

    4s24p5

    Kr

    4s24p6

    Rb

    5s1

    Sr

    5s2

    In

    5s25p1

    Sn

    5s25p2

    Sb

    5s25p3

    Te

    5s25p4

    I

    5s25p5

    Xe

    5s25p6

    Cs

    6s1

    Ba

    6s2

    Tl

    6s26p1

    Pb

    6s26p2

    Bi

    6s26p3

    Po

    6s26p4

    At

    6s26p5

    Rn

    6s26p6

    Fr

    7s1

    Ra

    7s2

    BNG 1.6. CU HNH ELECTRON LP NGOI V ST NGOI CA CC NGUYN T NHM B

    IB IIB IIIB IVB VB VIB VIIB VIIIB

    Cu

    3d104s1

    Zn

    3d104s2

    Sc

    3d14s2

    Ti

    3d24s2

    V

    3d34s2

    Cr

    3d54s1

    Mn

    3d54s2

    Fe

    3d64s2

    Co

    3d74s2

    Ni

    3d84s2

    Ag

    4d105s1

    Cd

    4d105s2

    Y

    4d15s2

    Zr

    4d25s2

    Nb

    4d45s1

    Mo

    4d55s1

    Tc

    4d65s1

    Ru

    4d75s1

    Rh

    4d85s1

    Pd

    4d105s0

    Au

    5d106s1

    Hg

    5d106s2

    La

    5d16s2

    Hf

    5d26s2

    Ta

    5d36s2

    W

    5d46s2

    Re

    5d56s2

    Os

    5d66s2

    Ir

    5d76s2

    Pt

    5d96s1

    Ac

    6d17s2

    Ch : c mt s bt thng cc nguyn t: Nb, Tc, W, Pd v Ru, Rh. CU HI T LNG GI

    1.1. Pht biu hai nh ca Bohr. Hy nu nhng u im v hn ch ca thuyt Bohr v cu to nguyn t. 1.2. Ni dung v biu thc ca nguyn l bt nh Heisenberg. p dng biu thc Heisenberg hy tnh Dx hoc Dv trong cc trng hp sau v cho nhn xt:

    Qu bng bn bay, bit m = 10g, x = 0,01mm.

  • 29

    Electron trong nguyn t, bit v = 106 m/s. 1.3. Ni dung ca thuyt sng vt cht v h thc De broglie. Tnh bc sng l ca sng lin kt vi:

    Chuyn ng ca mt t, khi lng m = 1tn, tc v = 100 km/h. Chuyn ng ca electron trong nguyn t vi tc v = 106 m/s Cho nhn xt.

    1.4. Ti sao ngi ta ni phng trnh Schrodinger l phng trnh c bn ca chc lng t? Hy cho bit khi nim v hm sng v ngha vt l ca 2. 1.5. Vit phng trnh Schrodinger i vi nguyn t hydro. Gii thch cc k ttrong phng trnh. Orbital nguyn t l g? 1.6. Vit biu thc ton hc ca hm sng m t trng thi c bn ca electron trong nguyn t hydro. T hm suy ra s phn b mt xc sut c mt ca electron nh th no? Th no l my electron? 1.7. Hy vit nhng biu thc tnh nng lng, momen ng lng, hnh chiu ca momen ng lng (trn mt phng xc nh) ca electron trong nguyn thydro v cho bit ngha ca cc s lng t. 1.8. Tnh nng lng m nguyn t hydro hp th khi electron chuyn t trng thi c n = 1 ln trng thi c n = 2. 1.9. Cho cc hm s c k hiu nh sau: n,l,m; Rn,l; Yl,m. Mi hm ny ph thuc vo nhng bin s no? ngha ca mi hm s ny. 1.10. Cc obital ton phn ca nguyn t ( ) c c trng bng 4 slng t. Hy cho bit cc gi tr c th c ca cc s lng t . T tnh sphn lp trong mt lp, s AO, s electron trong mt phn lp, trong mt lp.

    1.11. Hy cho bit hnh dng ca cc m my electron 2s; 2px; 3dxz; v ch r c im ca cc m my . S khc nhau gia cc m my 1s v 2s; 2pxv 2py, 2pz.

    1.12. Cho cc orbital nguyn t: 1s; 2s; 2px; 2py; 2pz. Hy vit cc k hiu AO tng ng vi cc s lng t n,l,m. 1.13. Xt cc AO sau y trong nguyn t hydro: 1,0,0; 2,1,1; 3,2,0 (cc orbital c c trng bng 3 s lng t n, l, m gi l cc orbital khng gian). Hy vhnh dng cc AO . 1.14. Quy tc Kleskovxky v gin cc phn mc nng lng i vi nguyn tnhiu electron. Gin ny c ngha nh th no?

  • 30

    1.15. Hy cho bit ni dung ca nguyn l vng bn v ngha ca nguyn l ny.

    1.16. Pht biu nguyn l Pauli v nu ngha ca nguyn l ny. 1.17. Gii thch ti sao mi b 4 s lng t di y khng th l b 4 s lng t ca mt electron trong mt nguyn t no :

    1.18. Hy lp bng cc gi tr 4 s lng t cho tng electron trng thi bnh thng ca nguyn t nit. 1.19. Pht biu quy tc Hund v nu ngha ca quy tc ny. 1.20. Vit cu hnh electron ca cc nguyn t c s th t z = 28; 36; 37; 42; 47; 53; 56; 80. Hy cho bit v tr ca nguyn t trong BTH v tnh cht ho hc c trng. 1.21. Gii thch v sao

    O (z = 8) c ho tr 2 cn S (z = 16) li c cc ho tr 2, 4, 6. N (z = 7) c ho tr 3 cn P (z = 15) li c cc ho tr 3, 5 F (z = 9) c ho tr 1 cn Cl (z = 17) li c cc ho tr 1, 3, 5, 7.

    1.22. Vit cu hnh electron ca cc ion: Cu+, Cu2+; Fe2+, Fe3+; Mn2+, Mn7+. 1.23. Vit cu hnh electron ca Ar. Nhng cation, anion no c cu hnh electron ging Ar? 1.24. Trn c s cu trc nguyn t c th phn cc nguyn t ho hc thnh my loi (khi)? Hy nu c im cu to electron ca mi loi (khi). 1.25. Pht biu nh lut tun hon cc nguyn t ho hc. Trnh by nhng nguyn tc sp xp cc nguyn t trong BTH. 1.26. Nu c im cu hnh electron ca cc nguyn t nhm IA v tnh cht ho hc c trng ca chng. 1.27. Nu c im cu hnh electron ca cc nguyn t nhm VIIA v tnh cht ho hc c trng ca chng.

  • 31

    1.28. So snh cu hnh electron ca cc nguyn t nhm IA v IB; IIA v IIB; IB v IIB.

    1.29. Hy gii thch s bin thin tun hon tnh cht ca cc nguyn t theo chiu tng in tch ht nhn (ly chu k 2 v chu k 3 lm v d). 1.30. Hy so snh s bin thin tnh cht ca cc nguyn t trong chu k nh v chu k ln (ly chu k 3 v chu k 4 lm v d). 1.31. Hy so snh v gii thch s bin thin tnh cht ca cc nguyn t trong mt nhm A v nhm B (ly nhm IIA v IIB lm v d). 1.32. Radi (Ra) z = 88 l nguyn t kim loi kim th. Hy cho bit nguyn t kim loi kim th tip theo s c s th t bao nhiu? 1.33. S nghin cu hin nay hng v iu ch cc nguyn t c s th t 112 v 118. Hy cho bit chng thuc loi nguyn t g (s, p, d,...)?

    Bi 2 LIN KT HO HC V CU TO PHN T

    MC TIU 1. nh ngha v nu c mi quan h gia cc i lng c trng ca lin kt. 2. Nu c bn cht v cho v d cc thuyt c in v lin kt. 3. Trnh by c nhng lun im c bn ca thuyt lin kt ho tr (VB). 4. Nu c nhng c im ca cc kiu lai ho v biu din c cu trc khng gian ca mt s phn t in hnh. 5. Trnh by c nhng lun im c bn ca thuyt orbital phn t (MO) v vit c cu hnh electron ca mt s phn t v ion.

    M U Tr mt s kh him, cc nguyn t khng tn ti c lp m chng thng lin kt vi

    nhau to nn cc phn t. Vy cc phn t c hnh thnh nh th no? Bn cht ca cc lin kt l g?

    Nm 1913 thuyt cu to nguyn t ca Bohr ra i th ch ba nm sau (1916) xut hin nhng l thuyt u tin v lin kt.

    Nm 1926 cc thuyt c hc lng t mi v lin kt ra i. 1. MT S I LNG C LIN QUAN N LIN KT 1.1. m in ca nguyn t

  • 32

    m in l i lng cho bit kh nng nguyn t ca mt nguyn t ht electron lin kt v pha n. cng ln th nguyn t cng d thu electron

    IA: Nng lng ion ho (cn gi l th ion ho) l nng lng cn tch mt electron ra khi nguyn t A. I cng ln th nguyn t cng kh nhng electron.

    EA: i lc electron, l nng lng to ra khi nguyn t A nhn c mt electron. E cng ln th nguyn t cng d thu electron.

    Ngi ta cn phn bit: th ion ho th nht, th hai hay i lc electron th nht, th hai tng ng vi vic tch (hay nhn) electron th nht, th hai. I v E thng c tnh bng n v eV.

    Trong phn ng: A + B AB Nu B A th electron lin kt s lch hoc di chuyn v pha nguyn t B. hnh thnh lin kt gia A v B c hai kh nng:

    Kh nng xy ra l kh nng no to ra nng lng ln hnKh nng th nht xy ra nu EB IA > EA IB T EB + IB > EA+ IB

    Tc l B >A Ngi ta quy c ly m in ca Li l 1 th cc nguyn t khc s c m in tng

    i nh sau theo thang m in ca Pauling. BNG 2.1. M IN CA NGUYN T MT S NGUYN T

    IA IIA IIIA IVA VA VIA VIIA

    H

    2,1

  • 33

    Li

    1,0

    Be

    1,5

    B

    2,0

    C

    2,5

    N

    3,0

    O

    3,5

    F

    4,0

    Na

    0,9

    Mg

    1,2

    Al

    1,5

    Si

    1,8

    P

    2,1

    S

    2,5

    Cl

    3,0

    K

    0,8

    Ca

    1,0

    Ga

    1,6

    Ge

    1,8

    As

    2,0

    Se

    2,4

    Br

    2,8

    Rb

    0,8

    Sr

    1,0

    In

    1,7

    Sn

    1,8

    Sb

    1,9

    Te

    2,1

    I

    2,5

    Cs

    0,7

    Ba

    0,9

    Tl

    1,8

    Pb

    1,9

    Bi

    1,9

    Po

    2,0

    At

    2,2

    Fr

    0,7

    Ra

    0,9

    Nhn xt: Trong mt chu k, t tri sang phi m in ca cc nguyn t tng dn. Trong mt nhm A, t trn xung di m in gim dn. Cc nguyn t kim loi kim c 1, Fr c nh nht. Cc nguyn t phi kim c 2, F c ln nht.

    1.2. Nng lng lin kt Nng lng ca mt lin kt l nng lng cn thit ph v mi lin kt v to ra cc

    nguyn t th kh. Nng lng lin kt thng k hiu E v tnh bng Kcalo cho mt mol lin kt.

    V d: nng lng ca lin kt H H trong phn t H2; EHH = 104 Kcal/mol. Nng lng lin kt cng ln th lin kt cng bn. i vi cc phn t c s lin kt ging nhau nhiu hn 2 ngi ta dng i lng nng

    lng trung bnh ca lin kt. V d:

    Trong phn t H2O c 2 lin kt O H EOH th nht bng 118 Kcal/mol EOH th hai bng 102 Kcal/mol. V vy EOH trung bnh bng 110 Kcal/mol.

  • 34

    Tng t nh vy, gi tr ECH trong CH4 l trung bnh cng nng lng ca 4 lin kt CH. 1.3. di lin kt

    di lin kt l khong cch gia hai nhn nguyn t khi hnh thnh lin kt. di lin kt thng k hiu r0 v c tnh bng (1 = 108cm).

    di lin kt cng nh th lin kt cng bn vng. BNG 2.2. DI LIN KT V NNG LNG LIN KT CA MT S LIN KT

    Lin kt Phn t r0 () E (Kcal/mol) C Cl CHCl3 1,77 75,8

    C F CH3F 1,38 116,3

    C C CnH2n + 2 1,54 79,3

    C = C CnH2n 1,34 140,5

    C C CnH2n 2 1,20 196,7

    H H H2 0,74 104,0

    O = O O2 1,21 118,2

    O H H2O 0,96 109,4

    S H H2S 1,35 96,8

    N H NH3 1,01 92,0

    Nhn xt: cc lin kt cng loi (v d Cl C v F C; O H v S H) khi E cng ln th r0 cng

    nh. 1.4. bi ca lin kt

    S lin kt c hnh thnh gia hai nguyn t cho trc c gi l bi ca lin kt. V d bi ca lin kt gia cc nguyn t C trong ethan, ethylen, acetylen ln lt l 1, 2, 3. bi ca lin kt cng ln th lin kt cng bn, nng lng lin kt cng ln v di lin kt cng nh (bng 2.2). 1.5. Gc lin kt (gc ho tr)

    Gc to bi hai mi lin kt gia mt nguyn t vi hai nguyn t khc.

  • 35

    Trong cc gc lin kt th gc 109028 (gc t din) nh phn t CH4 l gc bn vng nht. V vy trong qu trnh hnh thnh phn t, cc nguyn t c xu hng to c cc gc lin kt gn vi gc 1090 28.

    Nhng hp cht c gc lin kt 600 hay 900 nh cyclopropan, cyclobutan thng khng bn, d b v vng, cn cyclohexan thng tn ti hai dng: dng thuyn v dng gh l dng c cc gc lin kt gn vi gc 109028 hn.

    1.6. phn cc ca lin kt. Momen lng cc Trong nhng lin kt gia hai nguyn t khc nhau, do c s chnh lch v m in,

    electron lin kt b lch v pha nguyn t c in m ln hn, to ra y mt in tch m no vi mt t l % in tch nguyn t (thng k hiu ) cn nguyn t kia mang mt in tch dng. Khi ngi ta ni lin kt b phn cc.

    phn cc ca lin kt c nh gi qua momen lng cc (muy). Momen lng cc l mt i lng vect v c gi tr: = q. l

    vi q = e (e l in tch nguyn t v l t l %, < 1) q: in tch ca mi cc (culong) l: di lin kt (mt).

    : i lng vect, hng t nguyn t c nh sang nguyn t c ln

    c tnh bng culong.mt (C.m thuc h n v SI). Ngi ta cn hay s dng mt n v khc gi l bai (D). 1D = 3,3.1030 Cm.

  • 36

    Trong thc t momen lng cc v di lin kt c xc nh bng thc nghim. T c th tnh c gi tr in tch q ca cc v phn trm in tch . V d:

    Lin kt HCl c gi tr = 1,07 D hay 3,56.1030 Cm v di lin kt l = 1,28 hay 1,28.1010 m. T tnh c q v :

    i lng cn c gi l ion (% lin kt ion) ca lin kt cng HCl. Trong mt phn t phn cc ca mt lin kt cn ph thuc vo s phn cc ca cc lin

    kt khc. V d:

    Lin kt H O trong HNO3 b phn cc mnh hn so vi HNO2 l do nh hng ca lin kt N O th ba trong phn t ny.

    BNG 2.3. GI TR MMEN LNG CC CA MT S LIN KT

    Lin kt H F H Cl H Br H I N = O C = O (D) 1,91 1,07 0,79 0,38 0,16 0,11

    2. NHNG THUYT KINH IN V LIN KT Nm 1913 thuyt cu to nguyn t ca Bohr ra i th ba nm sau (1916) xut hin

    nhng thuyt u tin v lin kt ho hc. l thuyt lin kt cng ho tr v lin kt ion. Nhng thuyt kinh in ny u da trn quy tc bt t (octet). Xut pht t nhn xt sau

    y: Tt c cc kh him (tr Heli) u c 8 electron lp ngoi cng. Chng rt t hot ng ho hc: khng lin kt vi nhau v hu nh khng lin kt vi

    nhng nguyn t khc to thnh phn t, tn ti trong t nhin di dng nguyn t t do. V vy, cu trc 8 electron lp ngoi cng l mt cu trc c bit bn vng. Do khi hnh

    thnh phn t, cc nguyn t c xu hng lin kt vi nhau t c cu trc electron bn vng ca cc kh him vi 8 (hoc 2 i vi heli) electron lp ngoi cng.

  • 37

    2.1. Lin kt ion. Kossen (Ctxen c) 1916 Lin kt ion c hnh thnh gia nhng nguyn t ca hai nguyn t c s chnh lch

    nhiu v m in (thng 2). Nguyn t ca nguyn t c nh nhng hn 1, 2 hay 3 electron cho nguyn t ca nguyn

    t c ln khi to thnh cc ion dng v nguyn t nhn electron to thnh cc ion m c cu trc electron ging kh him. Cc ion dng v ion m ht nhau to thnh phn t. V d:

    Na Cl Na+ Cl NaCl 2s2 2p6 3s1 3s2 3p5 2s2 2p6 3s2 3p6

    Nh vy bn cht ca lin kt ion l lc ht tnh in gia cc ion tri du. Trong lin kt ion, ho tr ca nguyn t bng s in tch ca ion vi du tng ng. Trong

    v d trn Na c ho tr +1, Cl c ho tr 1. Lin kt ion l lin kt bn, nng lng lin kt kh ln ( 100Kcal/mol) Lc ht tnh in gia cc ion khng nh hng, mt ion dng c tc dng ht nhiu ion

    m v ngc li v vy ngi ta ni lin kt ion khng c nh hng v khng bo ho. Nhng hp cht ion thng dng tinh th bn vng. 2.2. Lin kt cng ho tr Lewis (Liuyt M) 1916

    Thuyt lin kt ion khng gii thch c s hnh thnh phn t v d H2, O2 ( = 0) hay HCl, H2O ( nh).

    Lin kt cng ho tr c hnh thnh gia cc nguyn t ca cng mt nguyn t ( = 0) hay gia nguyn t ca cc nguyn t c s chnh lch nh v in m (thng 2).

    Trong lin kt cng ho tr, cc nguyn t b ra 1, 2, 3 hay 4 electron dng chung mi nguyn t t c cu trc 8 electron (hoc 2e trong trng hp hydro). V d:

    H. . H H: H H H H2: : : : : : : : O = O O2

    N N N2 : : : C: : : ::: C::: O = C = O CO2 Cc electron gp chung c gi l cc electron lin kt, mt cp electron gp chung to ra

    mt lin kt v cng c biu din bng mt gch.

  • 38

    Trong hp cht cng ho tr, ho tr ca nguyn t bng s lin kt hnh thnh gia mt nguyn t ca nguyn t vi cc nguyn t khc hoc bng s electron m nguyn t a ra gp chung.

    V d: Trong phn t CO2 ho tr ca O l 2 ca C l 4, trong phn t NH3 ho tr ca N l 3 ca H

    l 1.

    Ngi ta phn bit hai loi lin kt cng ho tr: Lin kt cng ho tr khng phn cc hay lin kt cng ho tr thun tu. V d lin kt

    trong cc phn t H2, O2, N2... ( = 0), lin kt C H trong cc hp cht hu c. Trong cp electron lin kt phn b u gia hai nguyn t.

    Lin kt cng ho tr phn cc. V d lin kt trong phn t HCl, HF lin kt O H trong phn t H2O, N H trong NH3... Trong cp electron lin kt b lch v pha nguyn t c m in ln hn. H : Cl H: F H: O: H H: N: H

    Nh vy mc phn cc ca lin kt ph thuc vo m c th bin thin t 0 n 3,2. Do c th coi lin kt cng ho tr thun tu v lin kt ion l hai trng hp gii hn ca lin kt cng ho tr phn cc. Da vo c th nh gi gn ng mc ion ca mt lin kt gia hai nguyn t. Cl Cl H Cl Na+ Cl cng thun tu cng phn cc ion

    BNG 2.4. PHN TRM C TNH CA CC LIN KT

    0 05 1,0 1,5 1,7 1,8 2,0 2,5 3,0 3,2 c tnh lin kt ion %

    0 6 22 43 50 55 63 79 89 92

    c tnh lin kt cng ht %

    100 94 78 47 50 45 37 21 11 8

    Qua bng trn ta nhn thy khi = 0 lin kt mang 100% c tnh cng (lin kt cng thun tu), trong khi khng c lin kt ho hc no mang 100% c tnh ion.

    Lin kt cng tng i bn. Nng lng lin kt c hng chc Kcal/mol. 2.3. Lin kt cho nhn

    Lin kt cho nhn cn gi l lin kt phi c th xem l mt dng c bit ca lin kt cng. Trong lin kt ny cp electron dng chung ch do mt nguyn t a ra gi l cht cho, cn nguyn t kia c mt orbital trng gi l cht nhn.

  • 39

    V d:

    Nh vy iu kin hnh thnh lin kt cho nhn l cht cho phi c t nht mt i electron cha lin kt v cht nhn phi c orbital trng.

    Ngi ta thng dng du mi tn ch lin kt cho nhn. Tuy nhin trong thc t cc lin kt ny hon ton ging lin kt cng ho tr thng thng. 2.4. Lin kt hydro

    Lin kt hydro c hnh thnh nhng hp cht trong hydro lin kt vi nguyn t ca nguyn t khc c m in ln v bn knh nh nh N, O, F. Cc lin kt ny b phn cc v trn nguyn t H c mt phn in tch dng. Trong khi cc nguyn t N, O, F mang mt phn in m v do ngoi lin kt cng ho tr n cn c th tng tc vi cc nguyn t H ca phn t bn cnh hnh thnh mt lin kt yu gi l lin kt hydro. Cc lin kt ny thng c biu din bng nhng du chm. V d:

    Lin kt hydro gia cc phn t.

    V d: Lin kt hydro ni phn t: lin kt hnh thnh trong cng mt phn t.

    Lin kt hydro l lin kt yu, nng lng lin kt nh v di lin kt ln. Tuy nhin n c nh hng nhiu n tnh cht vt l v ho hc ca phn t. V d:

    H2O c nhit si cao hn nhiu so vi phn t tng t vi n H2S. Cc phn t hu c mang nhm O H c nhit si cao hn cc ng phn ca chng

    khng cha lin kt ny: alcol so vi ether; acid so vi ester...

  • 40

    Alcol tan v hn trong nc l do to c lin kt hydro vi nc. Lin kt hydro to ra gia cc nhm C = O v NH ca amin acid trong cc chui

    polypeptid duy tr c cu trc khng gian ca phn t protein. Lin kt hydro gia cc cp base b sung (A:::: T v G:::: X) trong cc phn t ADN lm

    cho ADN ng vai tr m di truyn. Tm li khi da trn thuyt cu to nguyn t ca Bohr v quy tc bt t, cc thuyt kinh

    in v lin kt cho php m t v phn loi mt cch n gin lin kt ho hc, t gii thch c mt s tnh cht ca phn t. Tuy nhin cc thuyt ny c mt s hn ch sau y:

    Nhiu hp cht hay ion khng t c cu trc 8 electron lp ngoi nhng vn tn ti mt cch bn vng, v d: NO, NO2, BH3, Fe2+...

    Cha ni c bn cht ca lc lin kt gia cc nguyn t trong phn t l g. Khng cho bit cu trc khng gian ca cc phn t. Khng gii thch c mt s trng hp, v d nh ti sao di cc lin kt ca phn t

    benzen li bng nhau trong khi n c biu din bng cc lin kt i v n xen k nhau. Phn t l nhng h ht vi m, v vy l thuyt v lin kt v cu to phn t phi c xy

    dng trn c s ca c hc lng t (CHLT). Nm 1927 ra i hai thuyt CHLT v lin kt b sung cho nhau nhng s dng nhng

    phng php tnh gn ng khc nhau. 3. THUYT LIN KT HO TR

    (vit tt l VB valence bond) hay cn gi l thuyt cp electron lin kt do Heiler, London (Haile, Lnn c) xng nm 1927, tip theo l Pauling, Sleiter (Polinh, Slyt M) pht trin. 3.1. S hnh thnh lin kt trong phn t H2

    Thuyt VB c ra da trn c s nghin cu s hnh thnh lin kt trong phn t H2. Lun im ch yu ca thuyt ny l khi to lin kt ho hc cc nguyn t vn gi nguyn

    cu trc m ch tng tc vi nhau theo tng cp electron. Mi nguyn t H c mt electron trng thi c bn 1s. Khi hai nguyn t H tin li gn

    nhau s c hai kh nng xy ra: Nu hai electron c s lng t spin cng du, khi khong cch r gim nng lng ca h

    tng lin tc, l trng thi khng bn, khng to ra lin kt ho hc. Nu hai electron c s lng t spin ngc du nhau, nng lng ca h gim dn, v ti

    khong cch r0 = 0,74 c gi tr cc tiu tng ng vi nng lng ES E0 khi h trng thi bn vng, trng thi hnh thnh lin kt (hnh 2.1a).

  • 41

    Hnh 2.1a, b. Trng thi nng lng ca h 2 nguyn t H (a) v s hnh thnh phn t H2

    Nu lu rng mi orbital s (m my s) c bn knh 0,53 th khi tip xc nhau khong cch gia hai ht nhn phi l 1,06. Trong khi khong cch khi hnh thnh lin kt ch cn 0,74. iu chng t khi hnh thnh lin kt, hai orbital s xen ph vo nhau, lm tng xc sut c mt electron vng gia hai ht nhn, mt in tch m tng ln gy ra s ht hai ht nhn v lin kt chng vi nhau. (Hnh 2.1b)

    Nh vy lc lin kt ho hc cng c bn cht tnh in. 3.2. Nhng lun im c bn ca thuyt VB

    T nghin cu ca Heiler v London v phn t H2, Pauling v Sleiter pht trin thnh thuyt lin kt ho tr.

    Lin kt cng ho tr c hnh thnh do s ghp i hai electron c thn c spin ngc du ca hai nguyn t lin kt, khi c s xen ph hai AO.

    Mc xen ph ca cc AO cng ln th lin kt cng bn, lin kt c thc hin theo phng ti s xen ph l ln nht.

    Trong thuyt VB ho tr ca nguyn t bng s e c thn ca nguyn t trng thi c bn hay trng thi kch thch. V d:

    Ho tr cc i ca mt nguyn t bng tng s AO ho tr (AO lp ngoi cng). V d cc nguyn t thuc chu k 2 c 4 AO lp ngoi cng 2s v 2p3 nn c th c ti a ho tr 4

    3.3. S nh hng lin kt. Lin kt (xch ma) v lin kt (pi)

  • 42

    Tu theo cch thc xen ph ca cc AO, ngi ta phn bit: lin kt , lin kt , lin kt (enta).

    Lin kt ho hc to ra do s xen ph cc AO trn trc ni hai nhn ca nguyn t c gi l lin kt xch ma. Lin kt c th hnh thnh do s xen ph cc m my s s, s p hay p p (hnh 2.2) hoc gia cc m my lai ho L L; L s; L p (xem phn 4.6)

    Hnh 2.2. S xen ph cc orbital khi hnh thnh cc lin kt v

    Nh vy khi to ra lin kt th t c s xen ph ln nht v vy lin kt xch ma l lin kt bn. Nu gia hai nguyn t ch c mt lin kt th lin kt lun lun l lin kt .

    Lin kt ho hc to ra do s xen ph cc AO hai bn ca trc ni hai nhn nguyn tc gi l lin kt pi. Lin kt c th hnh thnh do s xen ph cc m my p p, p d hay d d (hnh 2.2).

    So vi lin kt th lin kt bn hn v mc xen ph ln hn v vng xen ph nm trn trc ni hai nhn nguyn t.

    Khi gia hai nguyn t c t hai lin kt tr ln th ch c mt lin kt cn li l cc lin kt . V d:

    Trong phn t H2 c 1 lin kt do s xen ph 2AO s. Phn t Cl2 c 1 lin kt do s xen ph 2 AO p. Phn t O2 c 1 lin kt do s xen ph 2AO pxpx v 1 lin kt do s xen ph 2AO py

    py ca 2 nguyn t oxy. Tng t phn t N2 c 1 lin kt v 2 lin kt . Trong cc trng hp trn lin kt hnh thnh do s xen ph cc AO thun khit ss hay p

    p.

    4. S LAI HO CC AO TRONG LIN KT

  • 43

    + Khi nim lai ho c Pauling a ra trong khun kh thuyt VB. Ta hy xt s hnh thnh phn t CH4

    Nu khi hnh thnh phn t CH4 nguyn t C* s dng 4 AO (1 my s v 3 my p) xen phvi 4 my s ca 4 nguyn t H (mt lin kt hnh thnh do s xen ph ss v 3 lin kt do s xen ph ps). Nh vy l ra cc lin kt phi khc nhau (v d bn, gc lin kt) nhng trong thc t chng li hon ton ging nhau. iu ny c Pauling gii thch bng s lai ho cc AO.

    Khi lin kt cc nguyn t c th khng s dng cc orbital (cc m my) s, p, d thun m chng c th trn ln (hay cn gi l t hp) vi nhau to thnh nhng orbital mi hon ton ging nhau (gi l cc AO lai hay cc m my lai L).

    Nh vy: Lai ho l s t hp cc AO khc loi to ra cc AO hon ton ging nhau v hnh dng,

    kch thch v nng lng nhng c hng khc nhau. Khi c n AO tham gia lai ho s to ra n AO lai ho. c s lai ho, cc AO phi c nng

    lng khc nhau khng ln. V d: 2s 2p; 3s3p3d... Cc m my lai b dch chuyn so vi ht nhn nguyn t, mt u phnh to ra (u +) v

    do vy n s xen ph hon ton hn vi cc m my tng tc, to c cc lin kt ho hc bn vng

    + Di y l mt s kiu lai ho v nhng c im ca cc AO lai: 4.1. Lai ho sp

    S t hp mt AO s vi mt AO p to ra 2 AO lai ho c hnh dng, kch thc v nng lng hon ton ging nhau nhng hng theo 2 hng trong khng gian, trc ca 2AO ny to ra gc 1800. V d s lai ho cc AO trong nguyn t Be khi hnh thnh phn t BeH2

  • 44

    Hnh 2.3. Lai ho sp v s to thnh phn t BeH2

    4.2. Lai ho sp2

    S t hp mt AO s vi hai AO p to ra 3 AO lai ho c hnh dng, kch thc v nng lng hon ton ging nhau nhng hng theo 3 nh ca mt tam gic u, trc ca 3AO ny to ra gc 1200. V d s lai ho cc AO trong nguyn t B khi hnh thnh phn t BH3.

    Hnh 2.4. Lai ho sp2 v s to thnh phn t BH3

    4.3. Lai ho sp3

    S t hp mt AO s vi ba AO p to ra 4 AO lai ho c hnh dng, kch thc v nng lng hon ton ging nhau nhng hng theo 4 nh ca mt t din u, trc ca cc AO ny to ra gc 109o28. V d, s lai ho cc AO trong nguyn t C khi hnh thnh phn t CH4.

  • 45

    Hnh 2.5. Lai ho sp3 v s to thnh phn t CH4

    Ngoi cc kiu lai ho trn, cc nguyn t t chu k 3 tr i, cn c orbital d cng c ththam gia lai ho nh dsp2; dsp3; d2sp3 ln lt to ra 4, 5, 6 m my lai ho s c ni n phn 3.7.

    xc nh kiu lai ho, ngi ta thng s dng quy tc sau y: S lng orbital lai ho ca mt nguyn t trong phn t bng tng s lin kt xch ma m

    n to vi cc nguyn t xung quanh v s cp electron ho tr cha tham gia lin kt. V d: CH4 C c lai ho sp3 (4+0)

    C2H2 C .. sp (2+0)

    NH3 N c lai ho sp3 (3+1)

    H2O O ....sp3 (2+2)

    SO2 S.sp2 (2+1)

    4.4. Hnh hc phn t ca mt s hp cht H3C CH3 ethan

    Hnh 2.6. S xen ph cc orbital v hnh hc phn t ca ethan

    Mi C c lai ho sp3 to ra 4 orbital lai ho. Mt orbital lai ho to ra lin kt gia 2 nguyn t C. Cc orbital lai ho cn li to ra 3

    lin kt vi H. Phn t c 7 lin kt . Phn t c dng hnh hc 2 chp t din (hnh 2.6)

  • 46

    H2C=CH2 ethylen

    Hnh 2.7. S xen ph cc orbital v hnh hc phn t ca ethylen

    Mi nguyn t C c lai ho sp2 to ra 3 orbital lai. Mt orbital lai ho to lin kt gia 2 C v 2 lin kt gia C v H. AO p thun xen ph bn to 1 lin kt . Phn t c dng hnh hc 2 nh tam gic (hnh

    2.7).

    HC=CH acetylen

    Hnh 2.8. S xen ph cc orbital v hnh hc phn t ca acetylen

    Mi nguyn t C c lai ho sp. 2 orbital lai ho to 1 lin kt gia 2C v 2 lin kt gia C v H. 4 AO p thun xen ph bn tng i mt to 2 lin kt . Phn t c dng hnh hc thng

    (hnh 2.8).

    CH4 methan

    Hnh 2.9. S xen ph cc orbital v hnh hc phn t ca methan

    C c lai ho sp3. 4 orbital lai ho xen ph vi 4 AO s ca H to 4 lin kt . Hnh hc phn t c dng t din u. Gc lin kt 109o28. NH3

  • 47

    amoniac

    Hnh 2.10. S xen ph cc orbital v hnh hc phn t ca amoniac

    N c lai ho sp3. 3 orbital lai ho xen ph vi 3AO s ca H to 3 lin kt . Hnh hc phn t c dng chp. Gc lin kt l 107o18. H2O Nc

    O c lai ho sp3. 2 orbital lai ho xen ph vi 2AO s ca H to 2 lin kt . Hnh hc phn t c dng gc. Gc lin kt l 104o30.

    BNG 2.5. KIU LAI HO CA NGUYN T TRUNG TM V HNH HC CA MT S PHN T

    S lin kt

    S cp e cha lin kt Kiu lai ho Hnh hc phn t V d

    2 0 sp

    ng thng

    BeH2; CO2; CN

    3 0 sp2

    Tam gic phng

    SO3; CO32

    3 1 sp2

    Gc

    SO2

    4 0 sp3

    T din

    CH4; NH4+; SO42

  • 48

    3 1 sp3

    Chp

    NH3

    2 2 sp3

    Gc

    H2O

    5 0 sp3d

    Lc din

    PCl5

    6 0 sp3d2

    Bt din

    SiF62; [Fe(CN)6]4

    4.5. Lin kt khng nh c Phn t benzen c cu trc nh thy hnh 2.12. C 6 nguyn t C u c lai ho sp2. Mi C

    to 2 lin kt vi 2 C bn cnh v 1 lin kt vi H. Cc orbital p thun cn li (c trc vung gc vi mt phng ca cc lin kt ) xen ph vi nhau to ra cc lin kt . Nh vy cc electron c gii to trn c 6 nguyn t C (hnh 2.12). Ngi ta gi cc lin kt l cc lin kt khng nh c. Mt cch tng t cng thy cc phn t butadien v allen (hnh 2.13). Cc lin kt khng nh c c m t bng nhng du chm thay v cho cc gch (hnh 2.14). C6H6 Benzen

    Hnh 2.12. Cc orbital p thun v s hnh thnh lin kt khng nh c trong phn t benzen

    C4H6 butadien allen

  • 49

    Hnh 2.13. Cc orbital p thun v s hnh thnh lin kt khng nh c trong phn t butadien v allen

    Hnh 2.14. Biu din cc lin kt khng nh c trong phn t butadien, allen v benzen

    4.6. Lin kt trong phc theo thuyt lin kt ho tr v cu trc khng gian ca ion phc Theo thuyt ny s hnh thnh phc c thc hin nh tng tc cho nhn cc cp electron

    cha chia x ca cc phi t v cc orbital cn trng ca ion to phc. Nh vy: ion phc gm: Ht to phc (ion to phc) thng l ion kim loi khi d c cc orbital trng. Phi t, thng l ion hay phn t cn i electron cha lin kt (NH3, CN, Cl).

    V d 1: S to thnh phc [Cr(NH3)6]3+

    Cr z = 24 c cu hnh electron lp ngoi cng v st ngoi cng 3d54s1

    Ion trung tm Cr3+ c cu hnh electron lp ngoi cng v st ngoi cng 3d34s04p0

    y c s lai ho d2 s p3 to ra 6 AO lai ho (cn trng electron) hng theo 6 nh ca bt din v phc c hnh hc phn t dng bt din (hnh 2.15).

    S lai ho xy ra gia AO lp trong (3d) v cc AO lp ngoi (4s, 4p) v vy gi l s lai ho trong. Phc l thun t v c e c thn.

  • 50

    Hnh 2.15. Cc orbital lai ho d2 s p3 ca Cr3+ v s to thnh ion phc [Cr(NH3)6]3+

    V d 2: S to thnh phc [Ni(CN)4]2 Ni z = 28 c cu hnh electron lp ngoi cng v st ngoi cng 3d84s2

    ion trung tm Ni+2 c cu hnh electron lp ngoi cng v st ngoi cng 3d84s04p0

    V CN l phi t mnh (lin kt mnh vi Ni2+) nn c s dn p 2 electron c thn ca 3d vo 1 lng t.

    Hnh 2.16. Cc orbital lai ho d2 s p3 ca Ni2+ v s to thnh ion phc [Ni(CN)4]2

    y xy ra s lai ho trong d s p2 to ra 4 orbital lai ho nm trn mt mt phng hng theo 4 nh ca mt hnh vung. Phc c hnh hc phn t dng vung phng (hnh 2.16). Phc l nghch t v khng c e c thn. V d 3:

    Phc [NiCl4]2

    phc ny do Cl l phi t yu nn ch xy ra lai ho cc orbital lp ngoi 4 (4s, 4p) ngha l

    xy ra s lai ho sp3 = AO 4s + 3AO 4p

  • 51

    Hnh 2.17. Cc orbital lai ho s p3 ca Ni2+ v s to thnh ion phc [Ni(Cl)4]2

    V hnh hc phn t dng t din (hnh 2.17), phc ny c s lai ho ngoi nn km bn hn phc lai ho trong. Phc thun t v cn electron c thn.

    Cc cht c cc electron cha ghp i, b t trng ht gi l cht thun t. Ngc li cc cht trong cc electron ghp i, b t trng y c gi l cht nghch t.

    Thuyt VB cho php hnh dung c cu trc khng gian ca phn t, tuy nhin n khng gii thch c s hnh thnh mt s phn t, v d: H2+ (1e), He2+ (3e), cng nh tnh thun tca mt s phn t nh O2, NO,... 5. THUYT ORBITAL PHN T (VIT TT MO MOLECULAR ORBITAL) Mulliken, Hund (Maliken, Hun c) 1927 5.1. Lun im c bn ca thuyt MO

    Phn t c coi nh mt ht thng nht, trong electron lin kt chuyn ng (tng t nh nguyn t), trong mt in trng gy ra bi cc ht nhn v cc electron cn li.

    Trong phn t trng thi ca electron c m t bng cc MO (tng t nh nguyn t, trng thi ca electron c m t bng cc AO).

    Khi nguyn t i vo lin kt, cc AO ca chng t hp (xen ph) vi nhau to ra cc MO. C t hp 2AO th c 2MO.

    iu kin c s t hp l: + Nng lng cc AO phi xp x nhau. + Cc AO c s i xng ging nhau so vi trc lin kt. + S xen ph phi t c mc r rt. Trong phn t cc electron c phn b dn vo cc MO , *, , *, , cng theo

    mt s quy tc nht nh: nguyn l ngoi tr; nguyn l vng bn v quy tc Hund nh i vi electron trong nguyn t. 5.2. Khi nim v MO lin kt v MO phn lin kt

    tm ra cc MO Muliken v Hund s dng phng php t hp tuyn tnh cc AO (vit tt l LCAO Linear Combination of Atomic orbitals).

  • 52

    V d: i vi phn t H2+ cc MO (MO) c t hp t hai AOA v B ca nguyn t HA v ion

    HB+

    MO = C1A + C2B Kt qu thu c 2 hm (2 orbital phn t MO)

    Trong hm t hpMO = C1A + C2B C1 v C2 l nhng h s cho bit s ng gp ca cc AO vo MO. C12, C22 s l xc sut electron c m t bi A v B. Trong trng hp cc phn t

    ng hch (cc nguyn t ca cng mt nguyn t), y l hydro th C1 = C2 v C12 = C22. T C1 = C2

    Nh vy khi t hp 2 AO A v B ta thu c 2 hm: + = C1A + C1 B = C1A C1B

    T iu kin chun ho ca hm sng ngi ta xc nh c T :

    Khi trng thi electron trong phn t c m t bng hm + th xc sut c mt electron (+2) tp trung vng gia hai ht nhn nguyn t, to ra sc ht hai ht nhn vi nhau v lin kt c hnh thnh. MO c m t bng hm + c gi l MO lin kt (MOlk) (hnh 2.18 a).

    Ngc li, i vi hm th xc sut c mt electron chnh gia khong cch hai ht nhn bng 0 dn n lc y gia hai ht nhn, lin kt khng to thnh. V vy MO c m tbng hm c gi l MO phn lin kt, thng k hiu MO* (hnh 2.18 b).

  • 53

    Hnh 2.18 a, b. Xc sut c mt electron gia hai ht nhn nguyn t H khi hnh thnh (a) v khi khng hnh thnh lin kt (b)

    5.3. Cu hnh electron ca phn t Cc MO khi t hp cc AOS

    V d: Cc AO1S ca nguyn t H

    Hnh 2.19. Cc MO lin kt, phn lin kt v gin nng lng phn t khi t hp 2 AOs

    Cc MOlk v MO* c hnh dng i xng qua trc lin kt nh trn c k hiu l cc MO v * (hnh 2.19).

    Nh vy khi t hp hai AOS ta c hai MO: v *. Trong MO lin kt c nng lng thp hn nng lng ca cc AOS, cn cc MO phn lin kt * li c nng lng cao hn nng lng cc AOs. Ta c bc thang nng lng cc MO nh: 1S 1S*

    V vy trong phn t cc electron c sp xp trc ht vo 1S. V d:

    phn t H2+ (1e) c cu hnh e 1 He2+ (3e) 2 *1

  • 54

    H2 (2e)2 He2(4e) 2 *2

    Ch : khi t hp hai AO2s ta cng thu c 2S v 2S* nhng c nng lng cao hn, ngha l 1S 1S* 2S 2S*

    Cc MO khi t hp cc AO pz

    Hnh 2.20. Cc MO lin kt, phn lin kt v gin nng lng phn t khi t hp 2 AO pz

    Trong trng hp ny cc MOlk v MO* cng c dng i xng qua trc v vy c k hiu l z phn bit vi do cc AO s to nn (hnh 2.20).

    Cc MO khi t hp cc AO px hay AO py Nh vy khi t hp hai AO px thu c hai MO lin kt v phn lin kt, cc MO ny khng

    i xng qua trc lin kt v c k hiu x v x* vi nng lng x x* (hnh 2.21). Tng t nh vy i vi hai AO py thu c y v y* vi x = y x* = y*. T ta vit c cc MO theo trt t nng lng tng dn nh sau:

    (1)

    Vi bc thang nng lng ny ta c th vit c cu hnh electron ca cc phn t hai nguyn t ca cc nguyn t cui chu k 2 nh O, F, Ne.

  • 55

    Hnh 2.21. Cc MO lin kt, phn lin kt v gin nng lng phn t khi t hp 2 AO px

    i vi cc nguyn t u chu k 2 cc MO c bc thang nng lng sau:

    (2)

    vit cu hnh electron ca phn t ta phi tnh tng s electron ca phn t ri in vo thang nng lng tng ng theo nguyn l Pauli (mi MO ti a 2e), nguyn l vng bn (vo cc MO c nng lng t thp n cao v quy tc Hund) vi cc MO c mc nng lng nhnhau th phn b sao cho c nhiu electron c thn nht. V d:

    O2 (16e)

    N2 (14e)

    Lu : n gin ngi ta thng ch vit t cc MO 2s (ch tnh s electron lp ngoi cng). Khi ta c:

    O2

    N2

    Ne2 (20e)

    Cc gin nng lng tng ng ca cc phn t ny cho hnh 2.22a, b.

  • 56

    Trong thuyt MO ngi ta cng a vo khi nim bc lin kt ( bi lin kt) . c tnh theo cng thc:

    n: s e trn cc MO lin kt n*: s e trn cc MO phn lin kt

    Theo cng thc trn bi ca O2, N2, Ne2 tng ng bng 2, 3, 0. ca Ne2 bng 0 iu c ngha l khng tn ti phn t Ne2.

    Da vo cu hnh electron ngi ta cng bit c t tnh ca phn t: nu trong cu hnh electron c electron c thn th phn t l thun t, ngc li l nghch t.

    Hnh 2.22. a, b. Gin nng lng ca phn t O2 (a) v N2 (b)

    BNG 2.6. CU HNH ELECTRON CA MT S PHN T V PHN T ION

    A2 Cu hnh electron l () E(Kcal/mol) H2

    1 0,74 104,0

  • 57

    N2

    3 1,10 225,4

    O2

    2 1,21 118,2

    F2

    1 1,42 37,1

    O2+

    2,5 1,12 150,5

    Ne2+

    0,5

    Cu hnh electron v gin nng lng ca phn t hay ion dng AB (B A). V d: NO, CO, CN...

    Cu hnh electron ca cc phn t loi ny cng thuc dy (2). Nhng gin nng lng cc AO ca nguyn t B c xp thp hn (hnh 2.23a).

    BNG 2.7. CU HNH ELECTRON CA PHN T V ION DNG AB

    AB Cu hnh electron l () E(Kcal/mol) CO

    3 1,28 255,7

    NO

    2,5 1,15 162,2

    CN

    3 1,14 224,9

    Cu hnh electron v gin nng lng ca phn t dng AB (B A) V d:

    Phn t HF H: 1s1 F: 1s2 2s2 2p5

    V nng lng ca cc phn mc 1s v 2s ca F qu thp so vi nng lng 1s ca H nn trong trng hp ny ch xy ra s t hp AO 1s ca H vi mt AO pZ ca F to ra hai MO: v *. AO 2s v cc AOpx, py cn li ca F to ra cc MO khng lin kt, thng k hiu MOklk. Bc thang nng lng ca cc MO nh sau: tng ng vi gin nng lng hnh (2.23b).

  • 58

    Hnh 2.23 a, b. Gin nng lng ca phn t CO (a) v HF (b)

    6. S PHN CC CA PHN T Mt phn t c gi l phn cc khi trng tm in tch dng khng trng vi trng tm

    in tch m. Khong cch gia hai trng tm gi l di lng cc. Khi phn t ch gm hai nguyn t nu lin kt l phn cc th phn t cng phn cc v

    di lng cc chnh l di lin kt. V d, cc phn t HCl, HBr, CO, NO... l cc phn tphn cc.

    i vi nhng phn t gm nhiu nguyn t (t 3 nguyn t tr ln) ch phn cc khi trong phn t c lin kt phn cc v cc lin kt phn cc khng trit tiu nhau (tng cc vctmmen lin kt khc 0 hay phn t c cu trc bt i xng). V d: CO2, SO3, CCl4 l cc phn t khng phn cc v chng c cu trc i xng.

    Trong khi cc phn t H2O, SO2, CHCl3 l cc phn t phn cc v c cu trc phn tbt i xng

  • 59

    nh gi phn cc ca phn t ngi ta cng dng mt i lng gi l momen lng cc ca phn t, c k hiu

    q: in tch ca trng tm l: chiu di lng cc, y l khong cch gia hai trng tm in tch p.t cng c tnh bng C.m hay bai Phn t c hai nguyn t th momen lng cc ca lin kt chnh l momen lng cc ca

    phn t. Phn t c t hai lin kt tr ln th momen lng cc ca phn t bng tng momen lng

    cc ca cc lin kt

    Momen lng cc ca nhiu phn t c th xc nh c bng con ng thc nghim hoc tnh ton da vo momen lng cc ca lin kt:

    V d i vi phn t 3 nguyn t ABC, gi tr ca momen lng cc phn t c tnh theo s sau:

    = 12 + 22 + 21 2 cos Phn t CO2 c tng vect momen lin kt = 0 v vy

    khng phn cc. Phn t H2O c tng momen lin kt 2 = 212(1+ cos)

    0 ( =104o30 v 1 l momen lng cc ca lin kt OH). V vy nc l phn t phn cc.

    BNG 2.8. MOMEN LNG CC CA MT S PHN T

    Phn t BeCl2 CO2 SO3 H2O H2S SO2 NH3 CH3Cl

    p.t (D) 0 0 0 1,86 1,02 1,60 1,46 1,86

    Momen lng cc l mt thng s c li trong nghin cu cu trc ca phn t. S phn cc ca phn t c nh hng c bit n mt s tnh cht vt l ca phn t: cc

    phn t phn cc d dng tan trong dung mi phn cc v ngc li.

  • 60

    CU HI T LNG GI 2.1. nh ngha: nng lng ion ho, i lc electron v m in ca mt nguyn t. Biu thc tnh m in. 2.2. Nhng i lng c trng ca lin kt v mi lin h gia chng. 2.3. S phn loi cc lin kt da vo m in. Cho cc v d v nu cc iu kin, qu trnh hnh thnh cc lin kt ion, lin kt cng ho tr, lin kt cho nhn. 2.4. Theo quy tc bt t hy biu din lin kt trong cc phn t v ion sau y: H2O; NH3; NH4+; CO2; SO2; SO3; HNO2; HNO3; H2SO4.

    2.5. iu kin hnh thnh lin kt hydro so snh nng lng lin kt nng lng lin kt ion v lin kt cng ho tr. Nu nhng v d cho thy nh hng ca lin kt hydro n tnh cht vt l ca cc cht. 2.6. Thuyt ho tr lin kt (VB) c a ra trn c s nghin cu no? Hy nu nhng lun im c bn ca thuyt . 2.7. Cho v d, c im ca lin kt v lin kt . So snh v gii thch v bn ca hai lin kt ny. 2.8. Lai ho l g? c im cc m my lai ho sp; sp2; sp3. Cho cc v d vnhng hp cht c s lai ho ny. 2.9. Hnh hc phn t v s xen ph cc m my electron trong cc phn t:

    CH4; C2H2; C2H4; C2H6; NH3; H2O; SO2; SO3; CO; CO2.

    Trong cc phn t ny C; N; O; S c kiu lai ho g? 2.10. Hnh hc phn t ca cc phn t butadien, benzen, allen (CH2 = C = CH2). Cho bit cch biu din chng bng cng thc:

    c chnh xc khng? Ti sao? 2.11. Hy nu nhng lun im c bn ca thuyt orbital phn t (MO) v lin kt. Cc MO tm c da vo phng php no? ngha g ca cc MO? Th no l MO lin kt v MO phn lin kt (so snh v hnh dng v nng lng trong khng gian).

    2.12. Cu hnh electron v gin nng lng ca cc phn t dng A2 trong A thuc chu k 1 (H2+, H2, He2+, He2). Ti sao khng tn ti phn t He2. 2.13. Cu hnh electron v gin nng lng ca cc phn t dng A2 trong A thuc cc nguyn t cui chu k 2: O, F, Ne (O2, F2, O22,...). bi v t tnh ca chng?

  • 61

    2.14. Cu hnh electron v gin nng lng ca cc phn t dng A2 trong A thuc cc nguyn t u chu k 2: Li, B, Be, C, N (Li2, Be2, N2,...). bi v ttnh ca chng. 2.15. Cu hnh electron v gin nng lng ca cc phn t v ion dng AB: CN, CO, NO+, HF. bi v t tnh ca chng. 2.16. So snh di lin kt v bn lin kt trong cc ion v phn t: O2+, O2, O22, O2.

    2.17. Khi no mt lin kt b phn cc? Mt phn t phn cc? M men lng cc l g? Trong cc cht sau y phn t no phn cc? CO2, H2O, CHCl3, SO2, SO3 2.18. Ti sao CCl4 khng tan trong nc cn C2H5OH li tan v hn trong nc.

    Bi 3 NHIT NG HC

    MC TIU 1. Trnh by c ni dung ca nguyn l th nht ca nhit ng hc v nu c ngha ca cc hm trng thi: ni nng v enthalpy. 2. Vn dng c nhng nh lut ca nhit ho hc tnh ton hiu ng nhit ca nhng phn ng ho hc khc nhau. 3. Trnh by c ni dung v gii thch biu thc nguyn l th hai ca nhit ng hc. 4. Nu c ngha ca cc hm trng thi: entropy v nng lng t do trong nghin cu cc phn ng ho hc.

    M U Nhit ng hc nghin cu nhng quy lut chuyn ho gia cc dng nng lng khc

    nhau.

    C s ca nhit ng hc l hai nguyn l rt ra t kinh nghim sng ca con ngi. Cc nguyn l ny khng th chng minh bng con ng ton hc nhng nhng h qu rt ra t n khng mu thun vi thc tin.

    Nhit ng hc ho hc s dng nhng kt qu nghin cu ca nhit ng hc vo ho hc tnh ton thng bng v nng lng v rt ra mt s i lng lm tiu chun xt on chiu hng ca mt qu trnh ho hc.

    1. MT S KHI NIM V NH NGHA 1.1. H nhit ng hc: i tng m ta ang nghin cu v mt nhit ng hc. Ngoi h gi l mi trng.

  • 62

    H c lp: khng trao i vt cht v nng lng vi mi trng. H kn: khng trao i vt cht nhng c th trao i nng lng vi mi trng.

    1.2. Hm s trng thi: Cc i lng xc nh trng thi ca h. V d nhit , p sut, thtch, ni nng,...

    Nhng i lng l hm trng thi c c im l bin thin ca n trong bt k qu trnh no cng ch ph thuc vo trng thi u v cui m khng ph thuc vo cch din bin ca qu trnh. V d, bin thin ca th nng ca mt vt hai trng thi khc nhau ch ph thuc vo cao hai trng thi m khng ph thuc con ng a vt t trng thi ny sang trng thi kia.

    1.3. Qu trnh nhit ng: Khi h chuyn t trng thi ny sang mt trng thi khc ta ni h thc hin c mt qu trnh.

    Qu trnh ng tch: th tch khng i. Qu trnh ng p: p sut khng i. Qu trnh ng nhit: nhit khng i. Qu trnh on nhit: khng trao i nhit vi mi trng.

    2. NGUYN L TH NHT CA NHIT NG HC 2.1. Ni dung v cc cch pht biu

    Ni dung: tnh cht bo ton ca nng lng. Pht biu: Nng lng khng t sinh ra v khng t mt i m n ch c th chuyn t mt dng ny

    sang mt dng khc. (nh lut bo ton v bin ho nng lng ca Lmnxp) Khng th c ng c vnh cu loi 1. (ng c lin tc sinh cng m khng cn tiu tn

    nng lng hay ch cn mt lng ban u). Tn ti mt hm trng thi U gi l ni nng m bin thin ca ni nng khi h chuyn t

    mt trng thi ny sang mt trng thi khc (U) bng tng i s nng lng trao i vi mi trng trong qu trnh bin i ny.

    Nng lng ca mt h c lp lun lun c bo ton. 2.2. Ni nng Biu thc ca nguyn l I

    Nng lng ca mt h gm 3 phn: ng nng (nu h ang chuyn ng). Th nng (do h nm trong trng trng lc).

  • 63

    Ni nng. Trong nhit ng hc ngi ta nghin cu nhng h khng chuyn ng v tc dng ca

    trng hp dn l khng i v vy ch ch n ni nng. Ni nng: Nng lng tim tng bn trong mt vt hay h bao gm: + Tng ng nng (chuyn ng tnh tin, quay, dao ng) ca cc phn t, nguyn t,

    electron, ht nhn nguyn t. + Tng nng lng tng tc (th nng) gia chng. Ni nng (thng k hiu bng ch U) l mt hm trng thi v ng vi mi trng thi c

    mt gi tr ca U v bin thin U khng ph thuc vo qu trnh. Gi tr tuyt i ca ni nng khng xc nh c nhng bin thin ca n khi h chuyn t

    trng thi 1 c ni nng U1 sang trng thi 2 c ni nng U2. U = U2 U1 c th xc nh c qua lng nhit Q v lng cng A m h trao i

    (cho hoc nhn) trong qu trnh . U = Q +A (3.1)y l biu thc nguyn l I ca nhit ng hc. Lu : Theo quy c, nu h nhn c nng lng di dng nhit hay cng th Q v A c

    gi tr dng. Ngc li nu h sinh nng lng th Q v A c gi tr m. V d:

    Khi ni h phn ng to ra mt nhit lng l 100 Kcalo c ngha l Q = 100 Kcal Trong biu thc trn, cng A bao gm hai loi cng: Cng dn n Ad.n = P.V Cng c ch A' gm tt c cc loi cng khc m h trao i vi mi trng nh cng

    in, cng ho hc, cng c hc... Khi biu thc nguyn l I c dng: U = Q + A' P.V (3.2)

    Chng ta hy xem xt biu thc nguyn l I trong mt s v d sau y: V d 1:

    Ta hy hnh dung mt th nghim nh hnh 3.1. trng thi u h gm mt xilanh c pittong trong c mt l ng dung dch HCl v mt t km. Lc ny h c ni nng U1. Khi nghing xilanh thc hin phn ng gia acid v km, h to ra mt nhit lng Q v sinh ra mt cng dn n (cng chng p sut kh quyn P) And = P.V.

    Kt thc th nghim h nm trng thi cui c ni nng U2. Theo nguyn l I ta c:

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    U = Q P. V. V Q 0 nn U 0 iu ny c ngha l lng nhit to ra v lng cng m h thc hin c l do s gim

    ni nng ca h.

    Hnh 3.1. M hnh th nghim minh ho biu thc nguyn l th nht ca nhit ng hc

    V d 2: Hot ng ca mt chic pin: Nu hai cc ca pin c ni vi mt mt (v d mt ci qut) th trng thi u (khi

    cha ng cng tc) ton b h c mt ni nng l U1 chng hn. Sau khi ng cng tc v cho qut quay n khi dng, h sinh ra mt cng A (cng c nng) c ch. n trng thi ny hc mt ni nng l U2. Nh vy trong qu trnh ny c mt bin i ni nng U = U2 U1.

    Nu coi nhit to ra y l khng ng k (Q = 0), h khng thay i th tch (And = 0) th biu thc ca nguyn l th nht trong trng hp ny l:

    U = A' m A' 0 (v h sinh cng) Khi U 0. iu ny c ngha l cng in sinh ra y l do s gim ni nng ca h. Cng v d ny, nu pin ch ni vi in tr to nhit. Khi Q 0, Ad.n = 0, A' = 0) U = Q U 0. iu ny c ngha l nhit lng to ra trn in tr do s gim ni nng

    ca pin.

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    Hnh 3.2. M hnh th nghim minh ho biu thc nguyn l th nht ca nhit ng hc khi h ch sinh cng hoc ch to nhit

    2.3. Enthalpy

    Nh trn thy trong mt qu trnh ng tch V = 0 Ad.n = 0. Nu h khng thc hin cng c ch (A' = 0) th Qv = U.

    C ngha l nhit trao i trong mt qu trnh ng tch bng bin thin ca ni nng. Trong mt qu trnh ng p nu h khng sinh cng c ch ta c: U = Q P.V hay Qp= U + P.V Qp = U2 U1 + PV2 PV1 = (U2 + PV2) (U1 + PV1)

    K hiu U + PV = H ta c: Qp = H2 H1 = H Nh vy nhit trao i trong mt qu trnh ng p bng bin thin ca mt hm trng thi

    mi gi l enthalpy k hiu bng H. Ni nng v enthalpy c bn cht ging nhau, u l nng lng tim tng bn trong mt h hay vt bt k.

    H = U + PV hay H = U + P.V (3.3)Cc phn ng ho hc thng c thc hin trong iu kin p sut kh quyn khng i

    v nu khng c s tham gia ca cc cht kh (V = 0) th H = U; H = U

    3. NHIT HO HC 3.1. Hiu ng nhit ca phn ng (nhit phn ng)

    Trong mt phn ng ho hc, v d: A + B C + D Thng nng lng ton phn (ni nng hay enthalpy ca cc cht tham gia phn ng khc

    vi nng lng ton phn ca cc cht sn phm phn ng. Kt qu l sau phn ng c mt phn ni nng hay enthalpy b bin i. Phn ny c chuyn thnh nhit.

    Lng nhit to ra hay hp thu vo trong mt phn ng ho hc c gi l hiu ng nhit ca phn ng. Hiu ng nhit ca phn ng thng c k hiu bng bin thin ca enthanpy H (phn ng ho hc thng thc hin p sut khng i v khng sinh cng c ch).

    Phng trnh phn ng ho hc c ghi r trng thi ca cc cht v hiu ng nhit c gi l phng trnh nhit ho hc. V d:

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    C(r) +O2(k) CO2(k); H = 94,05 Kcal 3.2. nh lut Hess

    Hiu ng nhit ca mt phn ng ch ph thuc vo bn cht v trng thi ca cc cht u v cui m khng ph thuc vo cch thc din bin ca phn ng. V d, vi phn ng:

    Bng thc nghim ngi ta xc nh c: H1 = 94,1; H2 = 26,4; H3 = 67,6 Kcal H1 = H2 + H3

    3.3. Tnh hiu ng nhit ca phn ng da vo nhit sinh Nhit sinh ca mt cht l nhit ca phn ng to ra 1mol cht t cc n cht trng

    thi bn vng. V d:

    Lu : Nhit sinh xc nh iu kin 1 atm v 298oK c gi l nhit sinh tiu chun v k hiu l HS0.

    Nhit sinh ca cc n cht bn bng 0. BNG 3.1. NHIT SINH TIU CHUN, ENTROPY TUYT I

    V BIN THIN NNG LNG T DO SINH TIU CHUN CA MT S HP CHT

    Hp cht Cng thc Trng thi

    H0S (Kcal/mol)

    S0 (cal/mol.K)

    G0S (Kcal/mol)

    hydro H2 k 0 31,2 0

    oxy O2 k 0 49,0 0

    nit N2 k 0 45,8 0 clo Cl2 k 0 53,3 0

    carbon C r 0 1,4 0

    natri Na r 0 12,2 0

    nc H2O h 57,8 45,1 54,69 nc H2O l 68,3 16,7 56,74 carbon oxyd CO k 26,4 47,3 32,84

    cacbon dioxyd CO2 k 94,1 51,1 94,33

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    amoniac NH3 k 11,0 45,8 3,91

    amoniac NH3 dd 19,3

    hydroclorid HCl k 22,1 44,7 22,79

    hydrobromid HBr k 8,67 47,48 12,73

    hydroiodid HI k + 6,3 49,4 +0,31

    natri clorid NaCl r 98,6 17,32 91,87

    natri hydroxyd NaOH r 102,3 125,12 90,19

    anhydrid sulfur SO2 k 71,0 59,3 71,86 anhydrid sulfuric SO3 k 94,5 61,4 88,61

    methan CH4 k 17,9 44,5 12,15

    ethan C2H6 k 20,4 54,8 7,86

    ethylen C2H4 k +12,5 52,5 +16,3

    acetylen C2H2 k +54,2 48,0 +50,05

    benzen C6H6 l +11,7 64,4 +41,34

    ethanol C2H5OH l 66,4 38,4 41,81

    acetaldehyd CH3CHO l 39,8 63,56 32

    aceton CH3COCH3 l 59,3 47,55 36,73

    a.acetic CH3COOH l 115,7 38,2 93,18

    a.butyric C3H7COOH l 128,1

    a.benzoic C6H5COOH r 91,7

    a.fumaric C4H4O4 r 194,1

    a.sucynic C4H6O4 r 225,0

    L alanin C3H7NO2 r 134,6 30,91 88,56

    glycin C2H5NO2 r 128,5 24,76 90,36

    a.glutamic C5H9NO4 r 241,2

    a.aspartic C4H7NO4 r 233,3

    ure NH2CONH2 r 76,3 25

    ure NH2CONH2 dd 79,6 48,72

    Dglucose C6H12O6 r 304,6 219,24 sacarose C12H22O11 r 531,5 86,19 369,45

    glycerin C3H8O3 l 160,45 48,95 114,71

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    V d: Xc nh hiu ng nhit HX ca phn ng: Al2O3 + 3SO3 = Al2(SO4)3

    Bit HS0 399,1 94,5 821,0 Kcal/mol

    Theo nh lut Hess ta c: HX = H1 H2 HX = HS0 (sp) HS0 (tg) HX = 821 [3( 94,5) 399,1] = 138,5 Kcal. Hiu ng nhit ca mt phn ng bng tng nhit sinh ca cc cht sn phm tr i tng

    nhit sinh ca cc cht tham gia phn ng. V d 1:

    Tnh hiu ng nhit ca phn ng oxyho glucose iu kin tiu chun. C6H12O6 (r) + 6O2 (k) 6CO2(k) + 6H2O(l) Bit HS0 304,0 94,6 68,3 Hx0 = 6( 94,6) + 6( 68,3) ( 304,6 +0) = 670 Kcal.

    V d 2: Tnh hiu ng nhit ca phn ng thu phn ure thnh CO2 v NH3 (phn ng ny thc t

    khng xy ra nu thiu urease)

    Bit HS0 76,3 68,3 98,7 19,3 Kcal/mol Hx0 = [ 98,7 +2(19,3)] [76,3 + (68,3)] = 7,3 Kcal.

    3.4. Xc nh hiu ng nhit ca phn ng da vo nhit chy Nhit chy ca mt cht l nhit ca phn ng t chy 1 mol cht to ra cc oxyd

    cao nht.

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    V d: C2H5OH + 3O2 2CO2 + 3H2O Hc0= 327 Kcal/mol Lu : Nhit chy xc nh iu kin tiu chun c gi l nhit chy tiu chun v c k

    hiu l Hc0 Nhit chy ca cc oxyd cao nht bng 0. Bng 1.2. l gi tr nhit chy tiu chun ca mt s hp cht. Da vo bng nhit chy ta c

    th tnh c hiu ng nhit ca mt phn ng. V d:

    Xc nh hiu ng nhit HX ca phn ng: 2CO + 4H2 H2O + C2H5OH Bit: Hx0 67,6 68,3 326,7 Kcal/mol

    Theo nh lut Hess ta c: HX = H1 H2 HX = Hc0(tg) Hc0(sp) HX = [2( 67,6)+ 4(68,3)] ( 326,7) = 81,8 Kcal. Hiu ng nhit ca mt phn ng bng tng nhit chy ca cc cht tham gia tr i tng

    nhit chy ca cc cht sn phm phn ng. BNG 3.2. NHIT CHY TIU CHUN CA MT S CHT

    Hp cht Trng thi H0C (Kcal/mol)

    Hp cht Trng thi H0C (Kcal/mol)

    hydro k 68,3 phenol l 372,0

    methan k 212,8 aceton l 430,9

    ethan k 372,8 a.acetic l 208,3

    ethylen k 337,2 a.benzoic r 771,8

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    acetylen k 310,6 ethyl acetat l 538,0

    benzen l 783,4 anilin l 811,9

    naphthalen r 123,0 toluen l 934,5

    cloroform l 89,2 methanol l 173,7

    CCl4 l 37,3 ethanol l 326,7

    3.5. Nhng tnh ton da vo nhit nguyn t ho v nng lng lin kt Nhit nguyn t ho ca mt cht l nhit lng cn thit phn hu 1 mol cht th kh

    thnh cc nguyn t th kh. Nhit nguyn t ho c k hiu bng H

    V d:

    Nng lng ca mt lin kt l nng lng cn thit ph v 1 mol lin kt thnh cc nguyn t th kh.

    BNG 3.3. NNG LNG LIN KT TRUNG BNH CA MT S LIN KT

    7 Phn t E (Kcal/mol) Lin kt Phn t E (Kcal/mol)

    H H H2 104,2 O H H2O 110,0

    C H CH4 99,0 O H ROH 104,7

    C C C2H6 78,0 N H NH3 93,4

    C = C C2H4 140,0 N N 38,0

    C C C2H2 193,0 N N N2 225,4 C C C6H6 120,0 S H H2S 82,0

    C O C2H5OH 75,0 S = O 92,0

    C = O ceton 156,0 Cl Cl Cl2 58,0

    C = O aldehyd 150,0 H Cl HCl 103,2

    C = O CO2 168,0 C Cl RCl 75,8

    C N HCN 207,9 C N RNH2 65,9 O O H2O2 33,0 O = O O2 117,0

    Nng lng lin kt c k hiu bng E.

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    V d: EHH l nng lng lin kt gia hai nguyn t hydro trong phn t H2. Nng lng ny cng

    chnh bng nhit nguyn t ho ca H2.

    i vi phn t CH4 th v trong phn t ny c 4 lin kt CH. Mt cch tng t V d 1:

    Tnh nng lng lin kt O H trong phn t H2O bit:

    Theo nh lut Hess ta c:

    V d 2: Tnh nng lng lin kt C = C trong phn t C2H4 bit:

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    Theo nh lut Hess ta c: EC=C = 2HC(r) C(k) + 2EHH HS0 4ECH EC=C = 2.171,5 + 2.104,2 12,5 4.99,0 = 142,5 Kcal/mol

    V d 3: Tnh hiu ng nhit ca phn ng hydro ho ethylen: CH2 = CH2 + H2 C2H6 bit: EC=C = 142,5 Kcal/mol

    ECH = 99,0 Kcal/mol

    EHH = 104,2 Kcal/mol

    ECC = 78,0 Kcal/mol

    Theo nh lut Hess ta c: H = EC = C + EH H 2EC H EC C = 142,5 + 104,2 2.99,0 78,0 = 29,3 Kcal/mol

    Hiu ng nhit ca mt phn ng bng tng nng lng lin kt trong cc cht tham gia tr i tng nng lng lin kt trong cc cht sn phm phn ng.

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    4. NGUYN L TH II CA NHIT NG HC 4.1. Ni dung v cc cch pht biu

    Ni dung: Nguyn l th II cp n mt c tnh khc ca nng lng. l trong khi cc dng

    nng lng khc c th bin hon ton thnh nhit th nhit li ch c th bin mt phn thnh cc dng nng lng khc.

    Nghin cu nguyn l th II cho php rt ra mt s hm s trng thi lm tiu chun xt on mt phn ng nht nh c th t xy ra khng.

    Pht biu: Nhit khng th t truyn t mt vt lnh sang mt vt

    nng hn. Clausius 1850. Khng th c ng c vnh cu loi 2 l ng c bin

    hon ton nhit nhn c thnh cng (cng c ngha ng clm vic m khng chu mt s mt mt nhit no).

    Tn ti mt hm s trng thi gi l entropy k hiu l S m bin thin ca n trong mt qu trnh thun nghch S bng t s gia nhit lng trao i trong qu trnh v nhit ti xy ra s trao i nhit. Ngha l:

    (3.4)

    i vi qu trnh khng thun nghch:

    (3.5)

    Ta hy xem xt s mt my nhit Hiu sut ca my:

    (3.6)

    T c th i n kt lun: Hiu sut ca mt my nhit khng bao gi t c 100% v T2 khng khi no t c

    gi tr 0o tuyt i. iu ny cng c ngha khng th no bin hon ton nhit nhn c thnh cng (khng c mt mt nhit nng).

    V vy biu thc (3.6) c gi l biu thc ca nguyn l II. 4.2. Khi nim v entropy

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    4.2.1. Qu trnh t din bin Cc qu trnh t din bin l qu trnh t n c kh nng xy ra m khng cn tc ng t

    bn ngoi.

    V d: Nhm qu trnh A:

    Nc chy t ch cao n ch thp. Kh chuyn t ni c p sut cao n ni c p sut thp. Nhit truyn t vt nng sang vt lnh. Trong nhm ny h mt dn kh nng sinh cng (gim nng lng) v chuyn dn n trng

    thi cn bng. Nhm qu trnh B:

    Cc nc t chy thnh nc. S khuych tn vo nhau ca hai kh khc nhau. Nhiu phn ng phn hu cht cng t xy ra, v d: N2O4 2NO2 Trong nhm ny h chuyn t trng thi sp xp c trt t sang trng thi km trt t hn. Tt c cc qu trnh t din bin ni trn u khng th t xy ra theo chiu ngc li, chng

    l nhng qu trnh bt thun nghch. 4.2.2. Entropy

    Trong cc v d nhm A d dng tm thy tiu chun qu trnh t din bin. l schnh lch v cao (h), v p sut (p), v v nhit (T). Vy nhm B tiu chun tdin bin l g? V tiu chun no c th p dng chung cho cc qu trnh t din bin? l bin thin ca mt i lng mi S gi l entropy v k hiu l (S).

    V ngha vt l, entropy l thc o mc hn n ca vt cht: ng vi trng thi c trt t (t hn n) S c gi tr nh, h trng thi cng hn n S c gi tr cng ln.

    Trong nhit ng hc thng k ngi ta lin h mc hn n ca h vi mt i lng gi l xc sut nhit ng W.

    Theo Boltzmann, entropi c quan h vi W qua