Chng 1 Cc m hnh nguyn t

Chng 1

Cc m hnh nguyn t

1DemocritusNh trit hc Hy Lp ngi u tin t nn mng cho cc nghin cu v nguyn t cch y 2600 nm. Liu vt cht c th c chia nh mi c khng v u l gii hn ca s phn chia vt cht ?

400 BCL thuyt ca Democristus : Vt cht khng th phn chia thnh cc phn nh mi mi, s tn ti mt thnh phn nh nht cu to nn vt cht m ta khng th phn chia c na.Democristus t tn thnh phn nh nht ca vt cht l atomos , ngha l khng th phn chia (unable to devide)

2Atomosi vi Democritus, cc nguyn t l cc ht nh, cng, to nn t cng mt lai vt liu, nhng khc nhau v hnh dng v kch thcS lng nguyn t l v hn, lun di chuyn v c kh nng t hp vi nhau.

Tuy nhin, l thuyt ny b qun lng hn 2000 nm.Ti sao?Nh trit hc v i Aristokle v Plato : l thuyt cc k sai lm v cu to vt cht

Aristotle v Plato cho rng : vt cht cu to bi 4 yu t: t, la, khng kh, v nc. tng ny thng tr bi v a v ca hai nh trit hc v i. Do m tng v nguyn t b lng qun hn 2000 nm.

Dng thi gian ca l thuyt nguyn t M hnh Daltonu nhng nm 1800, nh ha hc ngi Anh thc hin nhiu th nghim v tha nhn s tn ti ca nguyn t.Tt c vt liu cu to nn bi nguyn t. Nguyn t l cc ht khng th phn chia v ph hy.Cc nguyn t ca cng mt nguyn t u ging nhau.Nguyn t ca nguyn t khc nhau th khc nhau. Hp cht c hnh thnh bng cch kt hp cc nguyn t ca 2 hay nhiu nguyn t..Trong cc phn ng ha hc, trt t cc nguyn t c sp xp li

L thuyt ny tr thnh mt trong nhng nn tng ca ha hc hin i.6M hnh Thomsons Plum Pudding

Nm 1897, nh khoa hc ngi Anh J.J.Thomson a ra bng chng u tin chng minh rng nguyn t c to ra bi cc ht thm ch nh hn.

Thomson nghin cu qu trnh phng in trong kh gas.Khi dng in truyn trong kh gas, n phng ra cc tia gm cc ht mang in tch m7M hnh Thomsoniu ny thc s gy ngc nhin cho Thomson, bi v cc nguyn t ca kh gas khng tch in. Vy cc in tch m n t u?

Where did they come from?Thomson kt lun rng cc in tch m n t bn thn nguyn t.Mt ht thm ch nh hn nguyn t tn ti Nguyn t c th phn chia cThomson gi in tch m l corpuscles, ngy nay tt c chng ta gi l electrons. V kh gas l trung ha, khng c in tch -> phi tn ti mt in tch dng trong nguyn t Nhng ng khng th tm ra n.M hnh Thomsonng a ra m hnh nguyn t m i khi gi l m hnh bnh mn Plum Pudding.Nguyn t c cu to bi mt m my in tch dng v cc ht mang in tch m gi l electrons..

Th nghim Rutherfords Gold FoilNm 1908, nh vt l ngi Anh Ernest Rutherford tin hnh thc nghim nhm vn tm mn b mt v cu to ca nguyn tRutherford bn mt chm ht tch in dng vo mt tm film bng vng mng (b dy khang 2000 nguyn t)

Kt qu th nghim ca Rutherford: - Hu ht cc ht truyn thng qua l vng

- Mt s t ht b lch hng (to ra cc chm sng trn mn hynh quang), trong mt s t b lch hng tr li

Nguyn t gn nh trng rngDo tng tc vi mt in tch dng c kch thc rt nh v tp trung hu ht khi lng nguyn t

12M hnh nguyn t hnh tinh ca Rutherford

Nguyn t hu nh trng rng , gm :

- Ht nhn c kch thc rt b so vi nguyn t, mang in tch dng v tp trung hu ht khi lng ca nguyn t. Xung quanh ht nhn l cc electron , mang in tch m chuyn ng trn cc qu o trn Tng in tch m ca electron bng in tch dng ca ht nhn nhng tri du , nn tan b nguyn t trung ha v in. M hnh ny ging nh hnh nh thu nh ca thi dng h, nn c gi l m hnh nguyn t hnh tinh.

L thuyt v tn x ht ca Rutherfordb : thng s va chm : gc tn x.T : nh lut bo tan nng lng nh lut bo tan moment ng lng.

: hng s lc CoulombT kt qu trn : - b rt ln => ln => ~ 0

- b gim => gim => tng ln

- b = 0 => => =

Nhng thiu st ca m hnh nguyn t hnh tinh ca Rutherford Khng gii thch c tnh bn vng ca nguyn t Khng gii thch c quang ph ca nguyn t l quang ph vch. Nng lng ca nguyn t :

Ngoi ra, do chuyn ng ca electron l chuyn ng u trn qu o trn

vi(F l lc Coulomb, f l lc qun tnh ly tm)Do electron luon bc x sng in t => E gim dn => |E| tng dn => r gim dn=> Electron chuyn ng xon c hng v tm nguyn t Do electron bc x sng in t lin tc => Quang ph ca nguyn t l quang ph lin tc, thc t, quang ph nguyn t l quang ph vch

M hnh mu nguyn t Bohr

T 2 thiu st ca m hnh nguyn t hnh tinh, Bohr tha nhn m hnh nguyn t hnh tinh v a ra hai tin ci tinTin 1: Tin v cc trng thi dng Nguyn t tn ti trong nhng trng thi c bit gi l trng thi dng c nng lng xc nh v gin an. Khi nguyn t trng thi dng, nguyn t khng bc x nng lng.

Electrons chuyn ng trn cc qu o dng c bn knh xc nh.

iu kin qu o dng tn ti: tun theo iu kin lng t ha moment ng lng.

L = mvr = n n l s nguyn , c gi l s lng t chnh.16M hnh mu nguyn t Bohr Tin 2 : Bnh thng nguyn t trng thi c bn c nng lng cc tiu (Emin = E0), khi b kch thch (cung cp nng lng), nguyn t chuyn ln trng thi kch thch, sau thi gian t = ~ 10-7 s, nguyn t chuyn xung trng thi c nng lng thp hn v bc x ra bc x c tn s .c bit : hp th c tnh la chn. h = E = E1 - E0 E0E1E3EE0E1E

Kt qu t m hnh nguyn t Bohr. 1 Bn knh qu o Do chuyn ng ca electron l chuyn ng u trn qu o trn

(F l lc Coulomb, f l lc qun tnh ly tm)iu kin lng t ha moment ng lng :

i vi nguyn t Hidro: Z = 1

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Kt qu t m hnh nguyn t theo Bohr 2 - Nng lng ca nguyn t :

vi

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i vi nguyn t Hidro : Z = 1

19Kt qu t m hnh nguyn t theo Bohr. 3. Cc dy quang ph ca Hidro:

l hng s RydbergViKhi nt = 1 : nc = 2, 3, 4, : Dy Lyman (trong vng t ngai)Khi nt = 2 : nc = 3, 4, 5, : Dy Balmer (4 vch u kh kin : lam chm tm, cn li l vch t ngai)Khi nt = 4 : nc = 4, 5, 6, : Dy Bracket(thuc vng hng ngai)Khi nt = 5 : nc = 5, 6, 7, : Dy Pfund(thuc vng vin hng ngai)Khi nt = 3 : nc = 4, 5, 6, : Dy Paschen(thuc vng hng ngai)

LymanBalmerPachen3. Cc dy quang ph ca Hidro

21M rng l thuyt Bohr cho cc ion ging Hidroe-in tch ht nhn : Ze+Ch c 1 electron ngoiIon ging Hidro

Ze+0

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120 Energy(eV)1n2123Z=1HZ=2He+Z=3Li2+nn123413.6 eV54.4 eV122.5 eV22Xy dng c m hnh gii thch c nhiu tnh cht trong quang ph Hydro. Cc dy quang ph BalmerTnh c hng s Rydberg kh ph hp vi gi tr thc nghimXy dng c biu thc tnh bn knh nguyn t Hydro.Tnh c cc mc nng lng trong nguyn t HydroC th m rng cho cc nguyn t ging Hidro

Thnh cng v hn ch ca thuyt BohrKhng gii thch c cu trc tinh vi ca cc vch quang ph (fine structure) S dng cc tin lng t ng thi li kt hp vi cc l thuyt c inTht bi trong gii thch cc nguyn t khc Thnh cngHn ch M hnh nguyn t ca Sommerfeld qu o hnh elipL thuyt ca Sommerfeld: ng vi cng mt s lng t n c th c n qu o khc nhau , trong ch c mt qu o trn c bn knh r v n-1 qu o hnh elip c1/2 trc di a v trc ngn b; trn mi qu o th electron c mt nng lng khc nhau.

S lng t chnh :

Trong : l s lng t phng v

iu kin lng t ha moment ng lng : l s lng t xuyn tm

v

24M hnh nguyn t ca Sommerfeld qu o hnh elipKch thc ca qu o c xc nh bi

Nu : => b = a qu o hnh trn (ging Bohr)

Nu : => b < a qu o hnh elip

xc nh hnh dng qu oM hnh nguyn t ca Sommerfeld Qu o hnh elipNng lng ca electron trn qu o:

Trong , l tham s a vo do nh hng ca thuyt tng i, ph thuc vo n v nDo , mc nng lng b suy bin bc n: Bohr SommerfeldL thuyt hin i : thay l = n - 1 , l = 0,1,,n-1l l s lng t phM hnh nguyn t ca Sommerfeld Qu o hnh elipCc dy quang ph nguyn t theo Sommerfeldn=3, n = 3, l = 2n=3, n = 2, l = 1n=3, n = 1, l = 0n = 2, n = 2, l = 1n = 2, n = 1, l = 0n = 1, n = 1, l = 0Qui tc la chn :

27Cc c ch kch thch nguyn tNhng c ch kch thch no kch thch electron nhy t trng thi c nng lng thp n trng thi c nng lng cao hn ? Nhit nng in trng Hp th bc x E0E1E1-Kch thch bng nhit

Nhit nng = k x T Dng l nung, tng dn nhit dn nhit thch hp s thy vch quang ph nhit phng E = 1.38 x 10-23 J/K x 300 K =25 meVKhuyt im : thiu chnh xc, cn nhit ln2-Kch thch bng in trngenhanh + A -> A* + echm

Dng in trng tng tc e kch thch nguyn t ln mt mc 1eV, cn phi cung cp in trng ln n 1018 V/m => Rt lnNng lng kch thch :

293- C ch hp th bc x :E0E1 = a. Hunh quang nh sng kch thch c bc sng nh sng pht ra c > . E0E12 > 1 > E2nh sng kch thch c bc sng nh sng pht ra c = . a. Cng hng 30