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Thuật ngữ tiếng Anh chuyên ngành Hóa học: Phần 2

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Tài liệu "Thuật ngữ tiếng Anh chuyên ngành Hóa học" phần 2 mở đầu mỗi chủ điểm có phần giới thiệu mục đích yêu cầu, phần bố cục bằng tiếng Anh và hướng dẫn đọc hiểu bằng tiếng Việt, kế tiếp là các nội dung căn bản có chứa trong chủ điểm. Để rèn kỹ năng đọc hiểu tiếng Anh Hóa học, sau mỗi nội dung trọng điểm chúng tôi có phần chú giải từ vựng và bài dịch mẫu – cuối chủ điểm là phần bài tập thực hành. Cuối sách có phần phụ lục danh mục từ vựng tiếng Anh Hóa học nhằm giúp bạn đọc hệ thống hóa các thuật ngữ chuyên ngành cần thiết.

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Nội dung Text: Thuật ngữ tiếng Anh chuyên ngành Hóa học: Phần 2

  1. ELECTRONIC CONFIGURATION OF THE ATOM Cftu HlMH a e C T R O N CO a NGUYEN TIT Myc DICH YEU cAu - O bjectives 4.1 To understand the dual nature of 4.5 To write electronic configurations Ina light and the relationships among shorter notation, using the concepts its energy, frequency, and wave­ of shells, subshells, and orbitals length 4.6 To draw the most common orbitals 4 .2 To use the Bohr theory of energy and to understand their spatial ori­ levels in atoms to explain light entation and the uncertain nature of emission and absorption by at­ locating the electron in the atom oms 4 .7 To represent pictorially the ener­ 4.3 To use quantum numbers to write gies of subshells in atoms and of the electronic structures of the the electrons that occupy the atoms in their most stable states subshells 4.4 To write detailed electronic configu­ 4 .8 To relate each element’s posi­ rations for the elements, using the tion in the periodic table to the permitted values for the individual electronic configuration of its at­ quantum numbers, the n + (. rule, oms, and to deduce electronic and the Pauli exclusion principle structures using the periodic table BO CUC - Layout 4.1 A Brief Exploration o f Light 4.2 Bohr Theory 4.3 Q uantum Numbers 4.4 Relative Energies o f Electrons 4.5 Shells. Subshells, and Orbitals 4.6 Shapes o f Orbitals 4.7 Energy Level Diagrams 4 .8 Periodic V ariation o f Electronic C o n figuratio n 100
  2. Jiuang dan doc hieu muc dich yeu cau vd bo cuc 4.1 Hieu duac ban chdt litdng tinh cua anh sang va cdc quan he gitfa ndng Itfong, tan sd va btfdc song cua anh sang, 4.2 Sd dung thuyet Bohr vi cdc btfdc ndng Itfong trong nguyen tii de gidi thich stf phat xa vd stf hdp thu anh sang bdi cdc nguyen tit, 4.3 Sd dung cdc sd litang tit de viet cdu true electron cua cdc nguyen tit trong trang thdi bin nhdt cua chung, 4.4 Viet cdc cdu hinh electron chi tiet cho cdc nguyen to, sit dung nhitng gid tri dtfac phep ddi vdi tilng sd litang tit rieng, quy ludt n+l vd nguyen ly loai trd Pauli, 4.5 Viet cdc cdu hinh electron theo mot cdch ghi ngdn gon, sd dung nhitng khdi niem vi cdc lap vd, cdc lap vd con vd cdc orbital, 4.6 Ve nhitng orbital thong dung nhdt vd hieu ditac stf dinh htfdng khong gian cua chung vd ban chdt khong xdc dinh cua viec dinh vi electron trong nguyen td, 4.7 Dien td bdng hinh anh cdc mile ndng litang cua cdc lap vd con trong nguyen td vd cdc electron chiem cho trong cdc lap vd con, 4.8 Lien he vi tri cua tilng electron trong bang phdn loai tuan hodn vdi cdu hinh electron cua cdc nguyen tit nguyen td dd vd suy ra dtfac cdu true electron bdng cdch sd dung bdng phdn loai tuan hodn. 4.1 Mot khao sdt ngdn gon ve anh sang , 4.2 Thuyet Borh, 4.3 Cdc sd litang td, 4.4 Ndng litang titang ddi cua cdc electron, 4.5 Cdc lap vd, cdc lap vd con vd cdc ocbital, 4.6 Hinh dang cua cdc orbital, 4.7 Gian do mdc nang litang, 4.8 Stf bien ddi tudn hodn vi cdu hinh electron 101
  3. Topic 4: Electronic configuration o f the atom In C hapter 3. you learned that atom s owe their ch a ra cte ristics to th e ir su b a to m ic p a r­ ticles— protons, neutrons, and electrons. Electrons occur in regions of space outside the nucleus, and the ele ctron ic structure is responsible for all of the atom s ch e m ica l properties and m any of its physical properties. The n um be r of e le c tro n s in a neutral atom is equal to the n um be r of protons in the nucleus. T h a t s im p le d e s c rip tio n e n ­ ables us to deduce m uch about atom s, espe cia lly co n c e rn in g th e ir in te ra c tio n s with one another (C hapter 5). H ow ever, a more detailed m odel of the atom e n a b le s even fuller explanations, including the reason for the d ifferen ce s b etw e en m ain group e le ­ m ents and ele m e n ts of the transition and inner transition series M any details p resented in this ch ap ter are based on m ath em a tics b eyo nd the scope of this course, so som e postu late s m ust be accepted as “ rules of the gam e " When the rules are follow ed, the e xplanations that result m atch the actua l p ro p e rtie s of the elem ents, w hich is a ssuran ce that the postulates are valid. Section 4.1 b rie fly d e scrib e s som e of the p hysical p ro p e rtie s of light, e s p e c ia lly the relationship of its w ave len gth to its energy. S ection 4.2 d e s crib e s how N iels B ohr d e ­ duced that e le ctron s o ccu r in shells having d istin ct ene rg ies. His th e o ry w as a m ile­ stone, but it does not e xplain the p ro pe rtie s of atom s o th e r th an h yd ro g e n . Section 4.3 introduces the q ua ntu m num bers, w hich provide a m ore s a tis fa c to ry p icture of elec­ tronic structure fo r atom s w ith m ore than one electron. The d e p e n d e n c e of the energy of an electron on its quantum num bers is discussed in Section 4.4. and shells, subshells, and orbitals are covered in S ection 4.5. The shapes of o rbitals are d e s c rib e d in S ec­ tion 4.6, and d ia gra m s dep ictin g the energy levels of su bsh ells are p re se n te d in S ec­ tion 4,7. The e le ctro n ic config uratio n of the atom is resp on sible for the ch e m ic a l and p hysical p ro p e rtie s of an e lem ent. The relatio n ship b etw e e n e le c tro n ic c o nfig uratio n and position on the perio d ic table is developed in S ection 4.8. Hifdng dan dpc hieu Trong chuang 3, ban da duac hoc la cdc nguyen tii co cdc dqc trung la do cac hat nguyen tU, ptoton, neutron vd electron. Cdc electron xuat luen trong nhdng uung khong gian ben ngoai hat nhdn vd cdu true electron chiu trach nhiein ve tdt ca cdc tinh chdt hoa hoc cua tinh chdt vat ly cua nguyen tit. So electron trong mot nguyen td trung lioa bang vdi so proton trong nhdn. Cdch mo td dan gian ndy giiip ta suy ra duac nhieu dieu ve nguyen tii, dac biet la nhdng dieu co lien quan den tuong tac cua mot nguyen td vdi mot nguyen tii khac (chi/cfng 5). Tuy nhien, mot mo hinh chi tiet han ve nguyen td con cho phep ta co nhdng giai thich ddy du han nda, ve nguyen nhdn cua nhdng khac biet gida cdc nhom nguyen to chinh, cdc nguyen to chuyen tiep vd cdc ddy chuyen tiep ben trong. Nhieu chi tiet duqc gidi thieu trong chuang ndy duqc dUa tren nhdng kien tlidc toan hoc ndm ngoai pham vi cua giao trinh ndy, do do mot so tien de phai duac chap nhan nhu cac luat chcn khi tuan theo nhdng luat chcn ndy, nhdng giai thich cho ra ket qua phu hap vdi cdc tinh chdt thuc te cua cdc nguyen to la mot dam bao bdng cdc tien de noi tren co hieu luc. M uc 4.1 mo td ngdn gon ve mot so tinh chdt vat ly cua anh sang, dac biet la quan he gida buac song vd ndng luang cua no Muc 4.2 mo td ve viec Niel Bohr da rut ra ket luan rdng cdc electron xuat hien trong cdc lap vd cd cdc ndng khac nhau nhu the nao. Thuyet ciia Niel Bohr la mot diem, moc quan trong. nhung no khdng giai thich duac tinh chat cua cdc nguyen td khdc han la hydro. M uc 4.3 gidi thieu cdc sd luang tu. rihung con sd ndy cung cap cho chung ta mot hinh anh thoa ddng han ve cdu true dieu tu cua cac nguyen td cd nhieu han mot electron Sit phu thuoc ve ndng luqng cua mot electron 102
  4. Topic 4: Electronic configuration o f the atom vdo cdc s6 luang tii cua no dupe ban trong muc 4.4, vd cdc lap vd, cdc lap vd con vd cdc orbital dupe ban den trong muc 4.5. Hinh dang cua orbital duac mo td a trong muc 4.6 i»a cdc gian do cho thdy cdc mile ndng luang cua nhilng lap vd con duac trinh bdy trong muc 4.7. Cdu hinh electron cua mot nguyen tii chiu trdch nhiem ve cdc tinh chdt hoa hoc vd vat ly cua nguyen to. Quan he gida cdu hinh electron vd vi tri trong bdng phdn loai tuan hodn duac trinh bdy trong muc 4.8. Chu diem 4.1: A Brief Exploration of Light W e saw in C h a p te r 3 that light from the Sun was broken into a spectrum and that a new e le m ent— helium — w as discovered, identified by the dark lines in that spectrum . It is e sse n tia l to learn at le a st a little a bo ut the p h ysica l natu re of lig h t in o rd e r to understand how the lines in the spectrum can tell us about energy levels in the atom s. V isible ligh t is a tin y fractio n of the electromagnetic spectrum, w hich includes gam m a rays, X -rays, u ltra vio let light, visible light, infrared light, m icrow aves, and radio w aves. The w ord light is som etim es used to m ean only visible light (the portion of the e lectrom agnetic sp ectrum d etectable by the hum an eye) and som e tim e s to m ean the entire e le ctrom ag ne tic spectrum . In this text, light w ill be used to m ean the entire e le c ­ trom agnetic sp ectrum , and w hen visible light is m eant, the word visible w ill be included. Light can be d escrib e d as a wave m otion because it can be refracted by a prism and diffracted by a grating. These phenom ena can be explained only by light p o sse ss­ ing wave properties. The wavelength (X) is the distance betw een tw o successive crests. The am plitude (A) is the m axim um displacem ent from the m ean position. The frequency (v) is the n um be r of cre sts that pass any point, such as point X, p er second. H ow ever, light also has a p article nature it can best be described as a stream of p articles called photons. The p ro pe rtie s of lights em itted by glow ing (red hot) objects and the p hoto­ e lectric effect can be e xplained only with light as a stream of particles. The energy of the photons (E) is related to the freq ue n cy of the w aves. T he fre ­ quency of a w ave (re prese n ted by v, G reek nu) is given by the equation E = hv w here h is a co n sta n t know n as Planck's constant with a value of 6.63 X 10-3 J/s. The 4 freq ue n cy of any w ave is inve rse ly proportional to its w avelength (A.). In the case of light, the p ro p o rtio n a lity co n sta n t is the ve lo city of light (c), equ al to 3 .00 X I08 m/s. (That value is equal to 186,000 miles per second) c Note that E and v are directly proportional, and both are inversely proportional to X . O nce any of th ese va lu e s is known for light, the other tw o can be ca lculated. Snapshot Review - On tap nhanh *- Light has both wave and particle properties. Its wavelength (X) is inversely propor­ tional to its frequency (v) and also to the energy of its photons: E = hv = h c /t . A. C alcu la te the e ne rg y of a photon of light if X = 3.00 X 10-* m. B. If the fre q u e n c y of light increases from red light to vio le t light, w ha t happens to the (a) e n e rg y of the photons? (b) w avelength? 103
  5. Topic 4: Electronic configuratitm o f the atom • Anh sang cd cd hai tinh chdt song va hat. Budc song ( X ) ciia no t l le nghich vai tan so (\) cua no vd cung ti le nghich vai nang luang cua cdc photon: £ = h v = h c / X A. Tinh nang litqng ciia mot photon anh sang neu X = 3 .00 x 10'm . B. Neu tan sd cua anil sang tang len tU anh sang do sang drill sang tim, dieu gi xay ra cho (a) ndng litang ciia cdc photon ?
  6. Topic 4: Electronic configuratitm o f the atom Chu diem 4.2: Bohr Theory_________________________________________ W hen gaseous atom s of a given elem ent are heated, they em it light of only sp e ­ cific ene rg ies. W hen gaseous atom s of that same elem ent absorb light, they absorb those sam e ene rg ies (see Figure 3 6) To explain these phenom ena of light emission and light absorption, N iels Bohr (1885-1962) (Figure 4 3) postulated that the e le c ­ trons in atom s are arranged in orbits, each with a definite energy The Bohr theory was the first to inclu de the explanation that electrons in atom s have discrete energy levels; that is. e le ctron s m ay be found only in orbits with sp ecific energies. W hen an atom abso rb s energy, an electron is "prom oted'' to a higher energy level. B ecause each o rb it has a discrete energy level, the difference in energy betw een the orbits is also d efinite. A fter an electron has been prom oted to a higher energy level, it falls back to a low er e nergy level W hen it falls back, light of energy equal to the d if­ ference in e ne rg y b etw een the orbits is em itted from the atom In a d ifferent e x p e ri­ m ent, w hen light is absorbed by the atom, the electron is raised from one orbit to a n ­ other one. B ecause there is the sam e energy difference betw een the orbits, the same energy of light is abso rb ed . An exam ple of these effects is show n. Som e of the p o s­ sible electron tran sition s in a hydrogen atom are diagram m ed B ohr postulated circu la r orbits for the electrons in an atom and developed a m ath ­ em atical m odel to re p re se n t the energies of the orbits, as well as their distances from the a to m 's n ucleu s. His m odel w orked very w ell for the hydrog en atom . It could be used to calculate the e ne rg y of the em itted and absorbed light, as w ell as the radius of the atom H ow ever, the inten sity of the various w ave len gth s of light involved was not e xp la in e d w ell M ore o ve r, no other atom was e xplain ed w ell at all It has since been rep la ce d by a q ua ntu m m echanical m odel, but B ohr's theory w as a m ilestone because Bohr w as the first to postulate energy levels in atom s S napshot Review - On tap nhanh B ohr p o stu la te d that the e lectrons in an atom revolved about the nucleus in circu la r o rb its and absorbed or em itted light when they changed from one orbit to another. *- B o hr's postu late that electrons have d istinct energy levels in atom s was a m ile ­ stone in the u nd ersta nd in g of the nature of the atom A If B o hr's th e o ry app lie s only to the hydrogen atom and it d oe sn't explain the inten sitie s of the spectral lines well, why is it im portant enough for us to study? B How m any d iffe re n t paths can the electron use to go from the fourth orbit to the first? • Bohr dd khdng dinh rdng cdc electron trong mot nguyen til quay quanh nhdn tren nhilng quy dqo hinh trdn ra hap thu hay phat xa anh sang khi chung thay doi tii mot quy dqo nay sang mot quy dqo khdc. • Tien de ciia Bohr cho rdng cdc electron trong nguyen til cd cdc mile ndng luqng khdc nhau Id mdt diem mdc quan trong de hieu duqc ban chat cua nguyen til. A. Neu thuyet Bohr chi dp dung dung cho nguyen til hydro cd ong khdng giai thich tot re a long do cua cdc rqch phd, tai sao no rdn kha quan trong de chiing ta phai tim hieuf B. Co bao nhieu Id trinli khac nhau md electron cd the sil dung de di til qu\ dao tlui til sang quy dao thii nhdt? 105
  7. Topic 4: Electronic configuration o f the atom Chu thich ta - cum ttf va htfong dan dpc hieu - light emission: phat sang - Bohr theory: ly thuyet Bohr - light absorption: hap thu anli sang - orbits; quy dau - difference: hieu so - discrete energy levels: mUc nang litang rdi rac Thuyet Borh Klu cdc nguyen tii khi ciia mot nguyen to dd cho diloc nung ndng. chiing phat xq anh sang clil theo nhilng ndng luqng ddc thu. Khi cdc nguyen tvt dang khi ciia cung nguyen to dd hap thu anh sang, chiing hap thu ciing nhilng ndng litqng dd (xem hinh 3.6). De gidi thich nhilng hien titqng ndy ciia sit phat xq vd sU hap thu anh sang. Niels Bohr (1 885-1962) (hinh 4.3) khdng dinh rdng cdc electron trong cdc nguyen tii duoc sdp xep tren quy dqo, mdi quy dqo cd mot ndng luqng xdc dinh. Thuyet Bohr la thuyet ddu tien gidi thich rdng cdc electron trong nguyen tit cd nhilng miic ndng htqng rieng biet; hie la, cdc electron cd the dilqc tim thdy chi tren nhilng quy dqo vdi cdc miic ndng htqng dqc thu. Khi mot nguyen tii hap thu ndng htqng, mot electron ditqc “ndng cap ’ len mdt mUc ndng luqng cao han. Vi mdi quy dqo cd mot miic ndng luqng rieng, chenh lech ndng luqng giUa nhilng quy dqo dd ciing xdc dinh. Sau khi mot electron dd duoc ndng len mot mUc nang luqng cao han, no rat trd Iqi miic ndng htqng thdp han. Klu electron rai trd lai, anh sang ciia ndng htqng bdng vdt chenh lech ndng htqng giUa cdc quy dqo duqc phat xq ra til nguyen tit. Trong mot thi nghiem khdc khi anli sang duqc hap thu bdi nguyen hi, electron duqc ndng len tit mot quy dqo sang mot quy dqo khdc, vi giUa cdc quy dqo cd ciing mot chenh lech ndng luqng, cd cung mot ndng luang anh sang duqc hop thu. Mot vi du ciia nhilng lueu Ung ndy ditqc trinh bdy tren. M ot so dich chuyen electron cd the cd trong mot nguyen tii hydro. Bohr thila nhan nhilng quy dqo hinh tron cho pliep electron trong mdt nguyen tii vd dd phat trien mot md hinh todn hqc de the luen ndng luqng ciia cdc quy dao cung nhu khodng cdch cua chiing tinh tit nhdn nguyen tit. Md hinh ciia ong dp dung rat dung cho nguyen til hydro. No cd the ditqc sit dung de tinh todn ndng htqng cua anli sang phat xa vd hap thu, cung nhu ban kinh ciia nguyen tii. Tuy nliien cudng dd cua cdc budc song anh sang khdc nhau cd lien quan khdng duqc gidi thich tdt. Ngoai ra, mo hinh ndy khdng gidi thich tdt cho mot nguyen tii nao khdc nUa. Md lunh nay sau dd duqc thay the bdi mot md hinh ca hqc litqng tii nhung thuyet Bohr van la mot diem moc quan trong vi Bohr 1a ngudi ddu tien khdng dinh cdc mite ndng luqng trong cac nguyen tii. Chu diem 4.3: Quantum Numbers Each electron in an atom is associated with a set of fo u r q uantum nu m b ers. The nam es of the qua ntu m num bers, along with th eir sym b o ls and p e rm itte d va lu es are given in Table 4 1 The p rin cip al quantum num ber (n) can have any p ositive in te g ra l va lu e but the ele ctron s in atom s in th eir m ost stable sta te s have p rin c ip a l q u a n tu m n u m b e rs with values from 1 th rough 7 only The m ost stable e le ctron ic state of an atom is ca lle d its ground state. Any higher energy state is called an excited state. (U nless "e xcited state" 106
  8. Topic /i: Electronic configuration o f the atom Table 4.1 The Quantum Numbers Name Symbol Permitted Values Examples Principal n Any positive integer 1,2,3,... quantum num ber A ngular m o m entum ( Any integer from 0, .... (n- 1) quantum num ber zero to (n — 1 ) M a g n etic in Any integer 0, quantum number from - f to + i l l i i Spin quantum num ber in 2’ ’ 2 2 ° r -2 is specified in later discu ssion , ground state is usually im plied.) The p rincipal quantum n um ber has the large st role in d eterm ining the energy of the electron, and it is also the m ain factor in d ete rm inin g how far the electron is. on average, from the nucleus. Thus, it is the m ost im p orta nt quantum num ber. For each value of n. the angular m om entum quantum num ber ( / ) for an e le c ­ tron can have integral values from zero to (n - 1) but cannot be as large as n The a ng ular m om en tu m q u a n tu m n um be r has a sm all role in d e te rm in in g the e ne rg y of the electron, and it d ete rm in e s the shape of the volum e of space that the electron can occupy (see S ection 4 6) For each va lu e of the a ng ular m om entum quantum n um be r ( f ), the m agnetic quantum num ber (m j has values ranging from - through zero to + in integral steps. The value of me does not o rdinarily affect the energy of an electron, but it does d e te r­ mine the o rien ta tion in space of the volum e that can contain the electron (Section 4 6). The spin q u an tu m num ber ( ms) m ay have a value of - 1 /2 or +1/2 only. The value of ms does not dep en d on the value of any o the r quantum n um be r The spin value gives the o rien ta tion of the m agnetic field associated with the electron. A n o th e r im p o rta n t lim ita tio n on the quantum num be rs of e le c tro n s in atom s, in addition to those listed in Table 4.1, is the Paul! exclusion p rinciple. This principle states that no two e le ctron s in an atom can have the sam e set of four quantum n u m ­ bers. This is like the b usine ss law that states that no two tickets to a rock co nce rt can have the sam e set of date and section, row. and seat num bers (Figure 4.7). The row num ber m ay dep en d on the section num ber, and the seat n um ber may depend on the row num ber, but the date does not depend on any of the o the r three. S im ila rly, the spin quantum n u m b e r is ind ep en d en t of the other three quantum num bers. T o g e th e r w ith the n + ( rule, d iscussed in the next section, the Pauli exclusion principle d e te rm in e s the n um ber of electrons in each of the shells in an atom Snapshot Review - On tap nhanh *- Each e le ctron in an atom has four quantum num bers, w hich govern its energy and d istan ce from the nucleus, am ong other things. The p erm itted values for the qua ntu m num bers are critical A W hat are the perm itted values for the principal quantum n um be r n9 B How m any d iffe re n t values of me ( are perm itted for an e lectron w ith an value of 2? 107
  9. Topic 4: Electronic configuratioti o f the atom • Moi electron trong mot nguyen tii co 4 so luong tU, 4 so nay chi phdi nang luang va khodng cdch tU nhdn cua electron, cung vdi nhilng thu khac niia. Car gia tri duqc phep cua cdc sd luqng tu la rat quan trong. A. Cdc gia tri duqc phep ciia sd luqng tu chinh n la g i? B Cd bao nhieu gid tri khdc nhau ciia m la duqc phep dot vai mot electron cd gia tri t bdng 2? Chu thich ttf - cum ttf va htfcmg dan dpc hieu - quantum numbers: cdc sd luqng til - principal quantum number: sd luqng tU chinh - excited state: trang thai bi kich thich - angular m o m entum quantum number: sd luqng tii dong luqng goc Cac so luong tur Moi electron trong mot nguyen tit cd lien quan vdi mot bo 4 sd luqng tU, ten got cun cac sd luang til cung vdi nhUng ky lueu vd nhilng gid tri duqc phep cua chung duqc cho trong b a n g 4.1. So luqng tii chinh In) cd the cd bat cU mot gid tri nguyen dua rig nao. nliUng cdc electron trong cdc nguyen til d trcing thai on dinh nhdt ciia cluing chi cd cdc sd luang til chinh cd gid tri tu 1 den 7 ma thoi. Trang thai electron ben nhdt cua mot nguyen til dilqc goi la mot trang thai co ban. Bat cU mdt trang thai ndng luqng nao cao hon cung duqc goi Id mot trang tlidi kich thich. ItrU khi "trang thai kich thich’' dilqc noi rd trong phdn sau, trang thai ndng liiqng thudng la de clii trang thai co ban) So luqng tii chinh cd mot vai trd Idn trong viec xdc dinh ndng luqng ciia electron, vd no cung la mdt yeu td chinh trong viec xdc dinh khodng cdch trung binh ciia electron ddi vdi nhdn. do do no la sd hfqng til quan trong nhdt. Doi vdi mdi gid tri ciia n, sd luqng tii ddng luqng goc fl) ciia mot electron cd the cd cdc gid tri nguyen tii 0 den In - 1) nhung khdng the Idn bdng n. Sd luqng tu dong luqng goc cd moi vai tro nhd han trong viec xdc dinh nang luqng cua electron, va no xdc dinli hinh dang ciia the tich khdng gian ma electron cd the chodng cho (xem muc 4.6). Hai ve cua ciing mot nhd liat khdng the cd ciing mot khu vUc, sd hang, so ghe va ngay tlidng. Sd luqng tii spin f m j chi cd the cd mot gid tri - \ hay + ‘ . Gid tri cua m khdng phu thuoc vao gid tri ciia bat cii mdt sd luong tii nao khdc. Gid tri spin cho biet su dmh huong ciia IU Irudng cd lien quan vdi electron. Mot gidi hqn quan trong nila ve cdc sd luqng III cua cdc electron trong nguyen tu ngoai nhilng dieu dd duoc het ke Irong bang 1.1, la nguyen ly loqi tru Pauli \gu\en U nay phat bieu rang kliong co hai electron trong cung mot nguyen tU cd the co cung mdt bo 4 sd luong tii. Dieu nay cung luong tu nhu mot doanh ngluep ludt phat bieu rang khdng cd hai ve xem nhqc rock cd the cd cung mot bo ngay thang. vd khu vUc. hang ghe vd sd ghe ngoi. Sd hang cd the phu thudc vdo sd khu vUc vd sd glie phai phu thudc i no sd hang, nhung ngay lliang kliong phu thudc vdo bat cii so ndo trong ba sd ndi tren Tuong tit, sd luong tU spin la dqc lap voi 3 sd luqng tU khdc. Ciing vdi quy luat n + 1 duoc ban den trong doan tiep theo, nguyen ly loai tru Pauli xdc dinh sd electron trong mdt lop vd trong nguyen tii. 108
  10. Topic 4: Electronic configuration o f the atom Chu diem 4.4: Relative Energies of Electrons The energies of the electrons in an atom are of param ount importance to the atom's properties. Electrons increase in energy as the sum n + ( increases. W e call this the n + ( rule. Thus, we can make a list of sets of quantum numbers in order of their increasing energies by ordering the electrons according to increasing values of n + . As a corollary, if two electrons have the same value of n + 1 , then the one with the lower n value is lower in energy. If the two n values are the same and the two , values are the same, then the electrons are equal in energy. In an atom, electrons with the same energy are said to be degenerate. Let’s determine sets of four quantum numbers for the electrons of the ground states of the atoms of the first 10 elements. Hydrogen has only one electron. For that elec­ tron to be in its lowest energy state, it needs the lowest possible sum of n and , so we will choose the lowest value of n: n = 1. Then, referring to Table 4.1, we determine values for the other three quantum numbers: With n = 1, the only permitted value of is 0. With = 0, the only permitted value of m# is 0. The value of ms can be eith er-1/2 or +1/2. The set of quantum numbers for hydrogen in its ground state can therefore be either of these: n = 1 or n = 1 ( = 0 ( = 0 m, = 0 m = , 0 m $ = - 1 /2 m t = +1/2 Since the n values and the ( values are the same in these two sets of quantum numbers, these possible configurations represent the same energy. Thus, either set of quantum numbers could represent the electron of hydrogen. A helium atom has two electrons, so we need two sets of quantum numbers. To represent the atom in its lowest energy state, we want each electron to have the low­ est energy possible. If we let the first electron have the value of 1 for its principal quan­ tum number, the set of quantum numbers for it will be the same as that given previ­ ously for the one electron of hydrogen. The other electron of helium can then have the other set of quantum numbers. First electron Second electron of helium of helium n = 1 n = 1 ( = 0 ( = 0 m, = 0 m( = 0 ms = -1/2 m s = +1/2 Both of these electrons have the same energy because they have the same n value and the same ( value Either one could have been chosen as the “first” electron. A lithium atom has three electrons. The first two of these can have the same sets of quantum numbers as the two electrons of helium. What should the set of quantum numbers for the third electron be? W e cannot choose the lowest permitted value for n. 109
  11. Topic 4: Electronic configuration o f the atom which is 1 because t and m would then both be 0. If we choose - 1 /2 as the value of ms, the third electron would have a set of quantum numbers exactly the same as that of the first electron, and if we choose the value mt = +1/2, the third electron would have the same set of quantum numbers as the second electron. Because neither of these situations is permitted by the Pauli principle, n cannot be 1 for the third elec­ tron. W e must choose the next higher value, n * 2. With n = 2, the permitted values of are 0 and 1. Because C = 0 will give a lower value for the sum n + , we choose that value for /. With I = 0, m ( must be 0, and we can choose either - 1 /2 or + 1/2 for m§. The quantum numbers for the electrons of the lithium atom can thus be as follows: First electron Second electron Third electron of lithium of lithium of lithium n = 1 n = 1 n = 2 ( = 0 ( = 0 ( = 0 m, = 0 m , = 0 m ,= 0 ms = -1/2 ms = +1/2 m$ = -1/2 (+1/2 With ms - 1/2 for its third electron, the fourth electron of beryllium (Be) will have n = 2,» (. = 0, me = 0 , and ms = +1/2. For the fifth electron of boron (B), we cannot use the combination n = 2 and = 0 because of the Pauli principle, so we use n = 2 and ( - 1. There are three possible values for mt with ( = 1, and together with the two possible values for ms, they yield six combinations of quantum numbers with n = 2 and I = 1. The configurations of the first 10 electrons in a multielectron atom are shown in Table 4.2. It must be emphasized that the value of and the sign of the mt value are arbitrary in some cases but not in others (see Problem 4.11 at the end of the chapter). W e can continue in this manner, building up the configuration of each elem ent by adding a set of quantum numbers for one “last" electron to the configuration of the element before it. This process of adding one electron to those of the preceding ele­ ment is called the buildup principle. The sets are shown in Table 4.3. Note that the combination n = 3. ( = 1 has the same sum of n and as n = 4, ( = 0 . Because the sum is the sam e, the combination with the lower n value is used for the thirteenth through eighteenth electrons because it is lower in energy. When we try to add the nineteenth electron to write the configuration for potas­ sium (K), we encounter a new situation. The combination with the next lowest sum of n and is n = 4, ( = 0 . The combination n = 3, t - 2 is higher in energy. The nine­ teenth through twenty-first electrons can have the following sets of quantum numbers: Quantum Nineteenth Twentieth Twenty-first number electron electron electron n 4 4 3 1 0 0 2 m, 0 0 -2 m5 _ i + ‘ _ 1 2 2 2 n + 1 4 4 5 I 10
  12. Topic 4: Electronic configuration o f the atom T ab le 4 .2 Possible Sets of Quantum Numbers for the Ten Electrons of Neon Q uantum num ber n I m , 1 F i r s t e le c t r o n 1 0 0 2 S e co n d electron 1 0 0 + i 1 T h ird electron 2 0 0 2 Fourth electron 2 0 0 1 F if t h e l e c t r o n 2 1 - 1 ~ 2 S ixth electron 2 1 0 + -; i S e v e n th electron 2 1 +1 2 1 E i g h t h e le c t r o n 2 1 - 1 + 2 1 N in th electron 2 1 0 Tenth electron 2 1 + 1 + .1 T ab le 4 .3 Possible Sets of Quantum Numbers or the Last Eight Electrons of Argon Quantum number n i in , in Eleventh electron 1 3 0 0 2 T w elfth electron 3 0 0 i T hirteen th electron 3 1 -1 2 Fourteenth electron 3 1 1 0 Fifteenth electron _ 1 3 1 +1 2 S ixte en th electron 3 1 -1 S e v en te en th electron 3 1 0 + ' E ighteenth electron 3 1 +1 + ' I I I
  13. Topic 4: Electronic configuration o f Ibe atom The fact that e le ctron s having quantum num ber values n = 4 and < - 0 are low er in energy than electrons w ith n = 3 and ( = 2 is of extrem e im p orta nce , it e x p la in s the existence and position on the p eriodic table of the tran sition m etals T his p o in t w ill be explained later S napshot Review - On tap nhanh The n + ' rule, the Pauli exclusion principle, and the p e rm itte d v a lu e s of the quantum n um bers enable us to d eterm ine the ord er of the e le c tro n s in an atom in increasing energy A tom s in th eir ground states have e lectrons w ith the lo w e s t p o ssib le values of n + I . * - If two e le ctron s have the sam e sum n + i but have d iffe re n t n values, the one with the low er n value is lower in energy A In each set. d ete rm in e w hich electron labeled X or Y. has the low er energy (a) X n = 4. i = 2 Y n = 4. ' = 1 (b) X: n = 3. t = 1 Y: n = 4. i = 0 (c) X: n = 5. I = 0 Y: n = 4, t = 2 • Quy luat n + 1, nguyen ly loai tru Pauli vd cdc gia tri cho phep cua cdc sd luqng tii chi giup chung ta xdc dinli duqc thii tit cua cdc electron trong mot nguyen tii theo ndng luqng tang dan. • Cac nguyen tii trong trang thai co ban cd cdc electron vdi nhdng gia tri n + I nhd nhdt cd the cd. • Neu hai electron co cung tong n + I nhitng cd cdc gid tri n khdc nhau, tin elec­ tron nao co gid tri n thdp hon thi co ndng luqng thdp hon. A. Theo tiing cap. xdc dinh electron nao, duoc ddnh ddu la X hay Y co ndng luong thdp hon fa) X : n = 4, i = 2 Y: n = 4, i = 1 (b) X: n = 3. ( = 1 Y n = 4. t = 0 (c) X: n = 5.' i = 0 Y n = 4. i = 2 Chu thich tCf - cum ttf va hUcmg dan dpc hieu - spin quantum num ber: sd luong tii spin - Pauli exclusion p rin c ip le : nguyen ly loai trii Pauli - buildup p rin c ip le : nguyen ly cdu tqo Nang lupng tuong doi cua cac electron Ndng luong cua cuc electron trong mot nguyen tii la het site quan trong doi rdi cdc tinh chi'it cua nguyen tu Cm electron gia tang l e ndng luong klu tong n + tang Ta got dieu do la quy luat n + Dtj i d\ ta co the tlntc luen mot bang het ke car v; / s ; r luqng tit theo thii tu ndng luong tang dan bdng cdch sdp xep cac electron theo j r gm I 12
  14. Topic 4: Electronic configuration o f tbe atom tri tang dan cua n + ( . Mot he qua neu liai electron co ciing gid tri n + ( , thi electron nao co gid tri n thdp lian se co nang luqng thdp han, neu hai gia tri n la bdng nhau va hai gid tri 1 cung bdng nhau thi cac electron co nang luqng bdng nhau. Trung mot nguyen tut cdc electron vai cung ndng luqng duqc goi la thoai bien (degenerate) Hay xdc dinh nhilng bo 4 so luqng tii cho cdc electron trong cdc nguyen tii a trang thai ca ban ciia 10 nguyen td dau tien. Hydro cd mot electron duy nhdt. De cho electron ndy d trang thdi ndng luqng tliap nhdt, no can phdi co tong n vd 1 nhd nhdt co the co, do dd cluing ta chon gia tri thap nhat ciia n. n = 1. Sau do xem bang 4.1, ta xdc dinh cdc gid tri cho ba sd luqng tii khdc. Vdi n = 1 chi cd mot gid tri dupe phep ciia ( la 0. Vdi ( = 0 chi cd mot gia tri duqc phep ciia m | la 0 Gid tri cua m s cd the la 1 /2 hay + 1 /2 Bo 4 sd luang tii dot vdi nguyen tii hydro d trang thai ca ban do dd cd the la mot trong cdc truang hqp sau ddy: n = 1 hay c • = 0 II ( = 0 m( = 0 m! = 0 ma= + Vi cdc gia tri n vd cdc gid tri ( la nhu nhau trong hai bo sd luqng tii, nhilng cdu inh cd the cd nay the hien cung mot ndng luqng. Do vdy bat cii bo sd luqng tii nao trong hai bo sd noi tren deu cd the bieu dien cho electron cua hydro. Nguyen tii helium co hai electron, vd do dd cluing ta can hai bo cdc sd luqng tii. De bieu dien nguyen tii trong trang thdi ndng luqng thdp nhdt ciia no. M ot electron can plidi cd ndng luqng thdp nhdt co the diiqc. Neu ta cho electron tlui nhdt cd gia tri sd luqng tii chinh la mot. thi bo cdc sd luqng tii cho electron dd se giong nhu ddi vdi electron cua hydro viia cho trudc dd. Electron cua helium cd the cd mot bo cdc sd IUqng tii khdc Eletron thu n h it Eletron thd hai cua helium cua helium n= 1 n= 1 i =0 1=0 m =0 m. = 0 mS = - 2 mS = + 2'- Ca hai electron nay cd cung ndng liiong vi cluing cd cung gia tri n la cung gia tri ' . Bat cii electron nao trong hai electron ndy cung cd the ditqc chon nhii electron "tlui nhdt” Mot nguyen tii lithium co ba electron, hai electron ddu co the cd cdc bo sd litqng tii nhu nhau nhu hai electron cua helium. Bo sd luqng tii cua electron tlui ba phai nhit the nao? Ta khdng the chon gia tri thong nhdt duqc phep cua n la ( vd I vd m klu do phai bdng 0. Neu ta chon - la gia tri cua thi electron tlui ba pliai cd bo cdc sd luqng tii chinh xdc giong nhu cua electron thu nhdt, vd neu ta chon gia tri m = + 1 /2 , thi electron thu ba phai cd cung bo so luqng tii nhu electron tlui hai. Vi ca hai tinh huong tren deu khdng duqc cho phep bdi nguyen ly Pauli, n khdng the bdng 1 ddi vdi electron tlui ba. Ta phdi chon gia tri cao han ke tiep n = 2. Vdi n = 2 cdc gid tri duqc phep ciia < Id 0 vd 1. Vi ( - 0 se cho ra mot gia tri thdp han cua tong n + ( , ta chon gia tri do 1 13
  15. Topic 4: Electronic configuration o f tbe atom cho I. Vdi < = 0, m, phai bdng 0, va chung ta chon m < = - 1 / 2 hay + 1 /2 , cac so luang til cho cac electron cua nguyen til lithi do do co the la nhu sau: electron thd nhdt electron thd hat electron thd ba cua lithi cua lithi cua lithi n = l n = l n= 2 1=0 ( =0 ( = 0 m, = 0 mt = 0 m, = 0 m = -\ m, = + l ,n . = ~2 (h a y + ) ) Vdi m = - ' cho electron thd ba, electron thd Id cua berylli (Be) se cd n = 2, 1 = 0 m / = 0 va m = + ' . Ddi vdi electron thd nam ciia boron (B), ta khong the sd dung to hap n = 2 va ( = 0 vi vi pham nguyen ly Pauli, do do ta sd dung n = 2 va 1 - 1 Co ba gia tri cd the cd cho m/ vdi 1 = 1 vd cung vdi hai gid tri cd the cd cho m chung cho ra 6 td hap cdc sd luqng td vdi n = 2 vd 1 = 1. Cdc cdu hinh cho 10 electron dau tien trong mot nguyen td nhieu electron duqc trinh bdy trong bang 4.2. Can phai nhdn manh rdng gia tri cua mlS va ddu cua gia tri m la tuy y trong mot sd trUdng hap nhilng khong duqc trong cdc trudng hap khdc (xem bai ta p 4.11 a cuoi chuang) Ta cd the tiep tuc theo cdch ndy de xay dung cdu hinh cho tdng nguyen td bdng cdch them mot bo cac sd luang td cho electron (cuoi cung) vdo cau hinh cua nguyen td trudc. Qua trinh them mot electron vdo nguyen td ddng trUac duac goi la nguyen ly tich luy. Khi chung ta thd them electron thd 19 vdo de viet cdu hinh cho Kali = 2 la cilc ky quan trong; no gidi thich cho sit . luen dien vdo vi tri tren bdng tuan hodn cua cdc kim loai chuyen tiep. Dieu nay se di/qc giai thich d phdn sau. Chu diem 4.5: Shells, Subshells, and Orbitals A shell is defined as a group of e lectrons in an atom all h aving the sam e principal quantum n um ber A s u b s h e ll is defined as a group of e le ctro n s in an atom all having the sam e princip al quantum n um ber and also the sam e a ng ular m om en tu m quantum num ber If two e le ctro n s in an atom have the sam e p rin c ip a l q u a n tu m n u m b e r the sam e a n g u la r m om en tu m qua ntu m num ber, and the sam e m a g n e tic q u a n tu m n u m ­ ber. the ele ctron s are said to be in the sam e o rb ita l. I 14
  16. Topic 4: Electronic configuration o f the atom Even though the m , and ms values do not affect the energy of the electron, it is s till im p o rta n t to learn about them . The n um ber of co m b in a tion s of perm itted values of these q ua ntu m num be rs determ ines the m axim um n um ber of e lectrons in a given type of subshell. For exam ple, in a subshell for w hich i = 1, mc can have three d iffe r­ ent values (-1 , 0. and +1). and ms can have two d ifferen t values (-1 /2 and +1/2). The six d ifferent com binations of m , and msallow a m axim um of six electrons in any subshell for w hich / = 1. W riting out each quantum n um ber value for every electron in an atom is very tim e- consum ing. A m ore e fficie n t m ethod is to group all the electrons in a given subshell. In this m ethod, the fo llo w in g four low ercase letters represent the possible PI values: V alue of Letter 0 s 1 P 2 d 3 1 B ecause only n and < values affect the energies of electrons, the electrons with the sam e n value and the sam e < value all have the sam e energy. In other w ords all the electrons in a given subsh ell are degenerate Each subshell is denoted by its p rin ­ cipal quantum n um ber and the letter designation for For exam ple, for neon, w ith atom ic num ber 10, the sets of quantum num bers for the 10 electrons are listed in Table 4 2 We can group them as follow s: Number of Subshell Value of n Value of electrons designation 1 0 2 Is 2 0 2 2s 2 1 6 Ip W e w rite the e le c tro n ic c o n fig u ra tio n by listing each subshell in order of increasing energy, w ith a su p e rscrip t giving the num ber of electrons in that sub-shell. That is, the detailed e le ctron ic co n fig u ra tio n for a neon atom is Ne Number of electrons in each subshell Principal quantum - Letter designation for number subshell based on angular momentum quantum number This co n fig u ra tio n is read aloud as follow s "one ess two, two ess two. tw o pee six " (The su p e rscrip ts are not exponents, so w ords such as square are not used ) The sum of the su p e rscrip ts is the total num ber of electrons in the atom Snapshot Review - On tap nhanh *- E le c tro n s in a g ive n sh ell all have the sam e n va lu e : e le c tro n s in a g ive n su bsh ell all have the sam e n value and the sam e C value: e le ctron s in a given o rbital all have the sam e n value, the sam e value, and the sam e m value I I5
  17. Topic 4: Electronic configuration o f the atom *- D etailed e le ctron ic configurations of elem ents give the su b s h e lls in increa sing o rder of ene rg ies w ith the n um ber of e le ctron s o cc u p y in g that s u b s h e ll as a right superscript. A G ive the d eta ile d e le ctro n ic co nfig uratio n of (a) Be, (b) M g B G iv e the de­ tailed e le ctron ic co nfiguration of Ar. • Cdc electron trong mot lap vd da cho tat cd deu cd cung gid tri n; cdc electron trong mot lap vd con dd cho tdt cd deu cd cung gia tri n vd cung gia tri 1; cdc electron trong mot orbital dd cho tdt cd deu cd cung gid tri n, cung gid tri 1 va cung gid tri m r • Cdu hinh electron chi tiet ciia cdc nguyen td duqc cho biet cdc lap vd con theo trat tU tdng dan ndng luqng vdi so electron chtia trong lap vd con do diiqc ghi bdng ti so nho d tren ben phai. A. Viet cdu hinh electron chi tiet cua (a) Be (b) Mg. B. Viet cau hinh electron chi tiet ciia Ar Chu thich tCf - cum til va hi/ong dan dpc hieu - electronic config uratio n: cdu hinh dien tii - subshell: vd con - square: vuong, binh phuang - o rb ita l: quy dqo Cac Idp vo, cac Idp vo con va cac orbital Mot Idp vd duqc dinh nghla la mot nhom electron trong mot nguyen tii, tdt cd deu cd cung sd luqng tii chinh. M ot lap vd con duqc dinh nghla nhu mot nhom cdc electron trong mot nguyen tii, tdt cd deu cd cung so luqng tii chinh vd cung cd cung so luqng tii dong luqng goc, neu hai electron trong mot nguyen tii cd cung so luqng tii chinh. sd luqng tii dong liiqng goc vd sd luqng tii til cdc electron do diiqc got la d tren cung mot orbital. Mac du cdc gia tri m va m khong anh huong den nang luqng cua electron, chung van quan trong de phdi hqc. So luqng to hqp cdc gia tri duqc phep ciia nhilng so luqng tii noi tren xdc dinh so luqng toi da ciia cdc electron mot kieu lap vd con cho trudc. Vi du, trong lap vd con cd I = 1, m l cd the cd ba gia tri khdc nhau (-1 , 0 va +1) vd m cd the cd lioi gid tri khdc nhau ( - 1 12va +112) Cd 6 td hqp cua m, vd m cho phep toi da cd 6 electron trong bat cii mot lap vd con nao cd t = 1. Viet tilng gia tri sd luqng tii cho mdi electron trong mot nguyen tii Id mdt viec rat mat thdi gian. M ot phuang phdp hieu qua han la nhom tdt cd cdc electron d trong mdt lap vd con dd cho. Trong phuang phdp ndy, 4 chd nhd ghi ben dudi sau day bieu dien cho 4 gid tri cd the cd ciia < : i cua Chi7 0 s 1 P 2 d J f Vi chi co cac gia tri n va I anh huang den ndng luang cua cac electron, t ac elec tron cd cung mot gid tri n va cung gia tri I deu cd cung ndng liiqng. S ot cach khac. tdt cd cdc electron trong mdt lap vd con dd cho deu la tlioai bien. Mdi lap vo con duar chi ra bdi sd luang tii chinh ra chd edi quy dinh cho
  18. Topic 4: Electronic configuration o f the atom 10, cdc bo so luang tii clio 10 electron duoc liet ke trong bdng 4.2. Chung ta cd the nhom chiing lai nhu sau: Gid tri ciia n Gid tri ciia I So electron Chi dinh lap vd con 1 0 2 Is 2 0 2 2s 2 1 6 2p Ta viet cau hinh dien tii bang cdch liet ke tiing lap vo con trong theo thii ti/ ndng luang tang dan, vai mot chi7 so ghi ben tren de chi so electron trong lap vd con do. Titc la cdu hinh electron chi tiet doi vdi mot nguyen tii neon la: Ne So electron trong moi lap cu So luang tii chinh o electron trong moi lap vo Cho chi dinh cho Idp vd con dila Iren so luong tu ddng luong got Cau hinh ndy ditac dqc len nhit sau "moi ess hai. hai ess hai, hai pee sdu" (chU so ghi tren khong phai Id sd md. do do cdc tit nhit binh phuang khdng duac sii dung). Tdng ciia cdc chH so ghi tren Id tdng so electron trong nguyen tii. Chu diem 4.6: Shapes of Orbitals An orbital is an allow ed energy state in an atom Each orbital is designated by the three quantum num bers n, ( , and m ( . Because ms is not specified, either value of can be used, and a m axim um of two electrons can occupy any given orbital in an atom. Know ing e xactly both the location and the m om entum of an electron in an atom at the sam e tim e is im p o ssib le This fact is know n as the H eise n b e rg u ncertainty principle. T he refo re , scien tists describe the probable locations of electrons. These lo ­ cations d e scrib e the orbital shapes, w hich are im portant w hen the atom form s bonds with other atom s, b eca use the orbital shapes are the basis of the geom etry of the re­ sulting m olecule It is equally pro ba ble that s orbital electrons will be located in any direction about the nucleus. W e say that an s orbital is spherically sym m etrical. The 1s orbital is p ic ­ tured B ecause an e le ctron with ( = 1 has three possible m values, any p su bshell has three o rb itals Each one lies along one of the coordinate axes - x , y, or z Each p orbital co nsists of tw o 3-d im e nsion a l lobes centered on one of the axes. An atom has five 3d orbitals, co rre sp o n d in g to the five possible m i values (-2. - 1 , 0. +1. and +2) for a subsh ell w ith ( = 2. S napshot Review - On tap nhanh * - The i orbitals are spherically sym m etrical. Do not m istake the individual lobes of the p and d orbitals as separate orbitals. • Cdc orbital s doi xiing can. Ditng nliarn Idn titng thin ciia cdc orbital p i d < 1 nhu nhilng orbital neng biet. I I7
  19. Topic 4: Electronic cotifiguration o f the atom Chu thich ttf - cum t il va htfcrng dan dpc hieu - Heisenberg uncertainty principle: nguyen ly khong on dinh cda Heisenberg - probable: cd le, xdc suat - orbital shapes: hinh dang quy dqo lobes: lobes Hinh dang cua cac orbital MoI orbital la mot trang thai nang luqng duqc phep trong mot nguyen til. Moi or­ bital duqc chi dinli bdi ba so luqng td n, 1 va m,. Vi mi khong duqc chi ro. gia tri nao ciia m cung co the duqc sd dung ua co toi da hai electron trong bat cd mot orbital cho trudc nao cda mot nguyen td. Viec biet chinh xdc cung luc cd ui tri vd dong luqng cda mot electron trung mot nguyen td la dieu khong the duqc. Thilc te ndy duqc goi la nguyen ly bat dinh Heisenberg, cdc nhd khoa hqc mo td nhdng vi tri xdc xuat cda cdc electron. Nhdng vi tri nay mo td cdc hinh dang cdc orbital, la dieu quan trong klu nguyen td tqo thanh hen ket vdi cdc nguyen td khdc, ui cdc dang orbital la nen tdng cho hinh dang hinh hqc cda phdn td duqc tqo thanli. Cdc electron orbital s co xdc suat de duqc tim thdy Id bang nhau theo bat cd hitdng nao tinh td nhdn. Ta noi rang mot orbital s co tinh ddi xdng cdu, orbital Is ri mot electron vdi n = 1 co ba gid tri m, cd the cd bat cd lap uo con p nao cung cd ba orbital. Moi Idp uo con ndm tren mot true tqa do x, y hay l. Moi orbital p gum 2 thdy ba chieu hitdng tdm, moi thuy ndm tren mot true. Mut nguyen Id cu 5 orbital p, tuong dug idi 5 gid tri co the co cda m t (-2 , 0, +1 ua +2) cho mot lap uo con vdi 1 = 2. Chu diem 4.7: Energy Level Diagrams ___________________ Energy level diagrams are models for portraying electrons' occupancy of an atom's orbitals. They help chemists predict how many electrons are in each orbital of a subshell. Electron occupancy of the individual orbitals is important in determining an atom s mag­ netic properties A line or a box or a circle is used to represent each orbital An energy level diagram that could hold the electrons of any known atom is shown in Figure 4 9. The energy level diagram is like a graph in one dimension: The higher a subshell is placed, the higher the energy of that subshell. The lines are spaced horizontally from left to right only to prevent crowding so that the diagram is easy to read The low est line on the energy level diagram represents the o rb ital in the Is subsh ell of the atom M uch higher in the diagram , indicating a m uch h ig he r e ne rg y lines for the orbitals of the 2p subshell. The third shell lies at an even hig he r e ne rg y and consists of an s su bshell a p subshell, and a d subshell. Note that the 3d s u b s h e ll lies at a slightly higher energy than the 4s subshell The order of energy in the d ia gra m is the same as that given by the n + i rule W e w ill o fte n fo c u s o u r a tte n tio n on th e p o rtio n o f th e e n e rg y le v e l d ia gra m c o n ta in in g the la s t e le c tro n a d d e d , in w h ic h w e a re m o s t in te re s te d T he orbitals that lie above that portion are assum ed to be em pty, and any o rb ita ls Delow those pictured are a lm ost alw ays com p le te ly filled w hen the atom is in its gro un d state We rep re sen t each electron with an arrow D ifferent e le ctron sp in s R v a l u e of - 1/2 or +1/2) are indicated by arrow s pointing dow nw ard or upw ard B e cau se each line 1 18
  20. Topic 4: Electronic configuration o f the atom represents one orbital, each line may hold a maximum of two arrows. If two arrows are present, they must be pointing in opposite directions. The energy level diagram representing the neon atom is shown in Figure 4.10. Hund's rule states that the electrons wi t hi n a gi ven subshel l remain as unpai r ed as possible. Moreover, if there is more than one unpaired electron in a given subshell, they all must occupy different orbitals and have the same electron spin (all arrows rep­ resenting unpaired electrons in a subshell point up or all point down) The energy level diagrams for the carbon, nitrogen, and oxygen atoms illustrate these rules: In the carbon atom, the lowest two subshells are filled: all electrons are paired in III II I I ~ 2p ~ 2p~ 2p ~ n u u 2s 2s 2s n u n 1s 1s Is Carbon atom Nitrogen atom Oxygen atom filled subshells. The 2p subshell has two electrons in the three orbitals, so each elec­ tron occupies a separate orbital. Moreover, both electrons have the same spin— both arrows point upward (alternatively, both could point downward). In the nitrogen atom, the 2p subshell is half filled. Each electron occupies a different orbital, and all arrows point in the same direction. In the oxygen atom, the 2p subshell is again partially filled. To get four electrons into the three orbitals requires the pairing of electrons in one orbital. In the other two. the electrons are unpaired and have the same spin: they are said to have parallel spin. The magnetic properties of atoms enable us to tell if all the electrons in an atom are paired or, if not. how many electrons are unpaired Atoms with all their electrons paired are repelled slightly from a magnetic field, and are said to be diamagnetic. If at least one electron per atom in a sample is unpaired, the sample tends to be drawn into a magnetic field, and are said to be paramagnetic. The greater the number of un­ paired electrons, the greater the attraction into the magnetic field (In elemental iron, cobalt, and nickel, the unpaired electrons in adjacent atoms reinforce one another, and a very much stronger attraction into a magnetic field results). S napshot Review - On tap nhanh *■ An energy level diagram shows the individual orbitals graphically with increas­ ing energy toward the top. Because only two electrons fit into any orbital (on any line), the electronic configuration of the atom can be deduced using such a diagram. Electrons in a given subshell occupy the orbitals singly with their spins aligned until the subshell is half full, after which they start to pair up A. How many unpaired electrons are present in the ground state of a sulfur atom 7 I 19
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