Ijiyomethri ye-VSEPR nobuhlobo bemolekyuli

Ukubala ama-electron domain azungeze i-athomu eyisisekelo

I-VSEPR iqala ngesakhiwo se-Lewis esilungile. Ezungeze i-athomu eyisisekelo, bala ama-electron domain: ibhangqa elilodwa ngalinye liyi-domain eyodwa, nesibopho ngasinye ku-athomu enye siyi-domain eyodwa noma siyisisodwa, esiphindwe kabili noma esiphindwe kathathu. Isamba sivame ukubizwa ngenombolo ye-steric. Isibopho esiphindwe kabili sibalwa kanye ngoba ama-electron aso athatha indawo efanayo phakathi kwama-athomu amabili.

Inombolo ye-steric ilungisa ijiyomethri ye-electron-domain, ukuhlelwa okugcina ama-domain kude kakhulu. Ama-domain amabili ayi-linear (180°), amathathu ayi-trigonal planar (120°), amane ayi-tetrahedral (109.5°), amahlanu ayi-trigonal bipyramidal (90° ne-120°), futhi ayisithupha ayi-octahedral (90°).

Ilebula emfushane igcina ukubala. Ekubhalweni kwe-AXₘEₙ, u-A i-athomu eyisisekelo, u-m inani lama-athomu abophelelwe u-X, no-n inani lamabhangqa amodwa u-E ku-athomu eyisisekelo. Amanzi yi-AX₂E₂: ama-athomu amabili abophelelwe namabhangqa amabili amodwa, inombolo ye-steric 4.

Ijiyomethri ye-electron-domain uma iqhathaniswa nesimo semolekyuli

Amabhangqa amodwa athatha isikhala, kodwa akayona ama-athomu, ngakho awabonakali egameni lesimo semolekyuli. Ijiyomethri yemolekyuli ichaza kuphela lapho ama-athomu ahlala khona. Uma kungekho mabhangqa amodwa ku-athomu eyisisekelo, amajiyomethri womabili ayafana; uma kukhona amabhangqa amodwa, ayahluka.

Ku-trigonal bipyramid izindawo azilingani: izindawo ezintathu ze-equatorial zihlukene ngo-120° nezindawo ezimbili ze-axial zingu-90° ukusuka ku-equator. Amabhangqa amodwa aya ezindaweni ze-equatorial kuqala, ngoba indawo ye-equatorial inabaseduze ababili kuphela ku-90° kanti indawo ye-axial inabathathu.

• Inombolo ye-steric 3: AX₃ trigonal planar; AX₂E bent, i-engeli engaphansi kuka-120°.
• Inombolo ye-steric 4: AX₄ tetrahedral; AX₃E trigonal pyramidal; AX₂E₂ bent, ama-engeli angaphansi kuka-109.5°.
• Inombolo ye-steric 5: AX₅ trigonal bipyramidal; AX₄E seesaw; AX₃E₂ T-shaped; AX₂E₃ linear.
• Inombolo ye-steric 6: AX₆ octahedral; AX₅E square pyramidal; AX₄E₂ square planar.

Kungani amabhangqa amodwa ecindezela ama-engeli ezibopho

Ibhangqa elilodwa liphethwe yinyukliya eyodwa kuphela, ngakho ukuminyana kwalo kwama-electron kusabalala kakhulu eduze ne-athomu eyisisekelo kunebhangqa elibophayo. Ukuphikisana ngakho kulandela ukulandelana ibhangqa elilodwa–ibhangqa elilodwa > ibhangqa elilodwa–ibhangqa elibophayo > ibhangqa elibophayo–ibhangqa elibophayo, futhi ibhangqa elilodwa ngalinye elingeziwe lingcindezela izibopho ezisele zisondelane.

Umndeni we-tetrahedral ukhombisa inkambiso. I-methane, CH₄, engenamabhangqa amodwa, inama-engeli e-H–C–H angu-109.5°. I-ammonia, NH₃, enebhangqa elilodwa, inama-engeli e-H–N–H amancane kancane. Amanzi, anamabhangqa amabili amodwa, ane-engeli ye-H–O–H engu-104.5°, inani elinikezwa ku-OpenStax Chemistry 2e. Izibopho eziphindwe kabili ziba nomphumela ofanayo, omncane, ngoba isibopho esiphindwe kabili siphethe ukuminyana kwama-electron okukhulu kunesisodwa.

I-VSEPR ibikezela ngokwethembeka isiqondiso salokhu kuphambuka, kodwa hhayi usayizi wakho oqondile. Lapho umbuzo ucela i-engeli kumolekyuli enamabhangqa amodwa, phendula ngokuthi "ngaphansi kancane" kunenani elifanele ngaphandle kokuba unedatha elinganisiwe.

Izibonelo ezisebenzile: i-chlorine trifluoride ne-xenon tetrafluoride

I-chlorine trifluoride, ClF₃. Ama-electron e-valence: 7 + 3(7) = 28. Izibopho ezintathu ezisodwa ze-Cl–F zisebenzisa ama-electron angu-6, futhi ukuqedela ama-octet amathathu e-fluorine kusebenzisa u-3 × 6 = 18, ukuze kube ngu-24. Ama-electron angu-4 asele aya ku-chlorine njengamabhangqa amabili amodwa. I-chlorine inezibopho ezintathu namabhangqa amabili amodwa, ngakho i-AX₃E₂ enenombolo ye-steric engu-5 nejiyomethri ye-electron-domain ye-trigonal bipyramidal.

Womabili amabhangqa amodwa athatha izindawo ze-equatorial. Lokho kushiya i-fluorine eyodwa endizeni ye-equatorial nezimbili ezindaweni ze-axial, ngakho ama-athomu akha isimo se-T. Amabhangqa amodwa aphusha ama-fluorine e-axial ku-equatorial, ngakho ama-engeli e-F–Cl–F angaphansi kancane kuka-90°. Ama-dipole amathathu ezibopho ze-Cl–F awakhanseli esimeni se-T, ngakho i-ClF₃ ihlukanisiwe.

I-xenon tetrafluoride, XeF₄. Ama-electron e-valence: 8 + 4(7) = 36. Izibopho ezine ze-Xe–F zisebenzisa ama-electron angu-8 futhi amabhangqa amodwa e-fluorine asebenzisa u-4 × 6 = 24, ukuze kube ngu-32. Ama-electron angu-4 asele ngamabhangqa amabili amodwa ku-xenon. Ngezibopho ezine namabhangqa amabili amodwa, i-xenon i-AX₄E₂, inombolo ye-steric 6, ijiyomethri ye-electron-domain ye-octahedral.

Ku-octahedron yonke indawo iyalingana, ngakho ibhangqa lokuqala elilodwa lingaya noma yikuphi; elesibili liya ngqo ngakwelinye, 180° ukusuka kulo, ukunciphisa ukuphikisana kwebhangqa elilodwa–ibhangqa elilodwa. Ama-fluorine amane bese elala endizeni eyodwa ku-90° nabaseduze babo: square planar. Isibopho ngasinye se-Xe–F sihlukanisiwe, kodwa izibopho eziphambene zikhomba ngqo ezinhlangothini eziphambene, ngakho ama-dipole ayakhansela futhi i-XeF₄ ayihlukanisiwe.

Ukwengeza ama-dipole ezibopho ukuthola ubuhlobo bemolekyuli

Isibopho phakathi kwama-athomu e-electronegativity ehlukile siyahlukaniswa, nesibopho esingelihle ngokwengxenye (δ−) ku-athomu ene-electronegativity enkulu. I-dipole yesibopho ngayinye inosayizi nesiqondiso, ngakho iziphatha njenge-vector. Isikhathi se-dipole semolekyuli yisamba se-vector sawo wonke ama-dipole ezibopho, ngokuvamile sibikwa nge-debye (1 D ≈ 3.336 × 10⁻³⁰ C·m).

Ama-dipole ezibopho ayakhansela lapho izibopho ezifanayo zihlelwe ngokulinganayo zizungeza i-athomu eyisisekelo. Lokho kwenzeka kumamolekyuli e-AX₂ linear, AX₃ trigonal planar, AX₄ tetrahedral, AX₅ trigonal bipyramidal ne-AX₆ octahedral lapho wonke ama-athomu e-X efana, futhi nasezimeni ze-AX₄E₂ square planar ne-AX₂E₃ linear, lapho amabhangqa amodwa ahlelwe ngokulinganayo futhi isibopho ngasinye sikhomba ngqo ngakwesinye esifanayo. Ezinye izinhlanganisela zesimo nezindawo zokuhlanganisa ngokuvamile zishiya i-dipole eyiyo.

Ukuqhathanisa okusebenzile: i-sulfur dioxide ne-sulfur trioxide. I-SO₂ inama-electron e-valence angu-6 + 2(6) = 18; isakhiwo sayo se-Lewis sibeka ama-domain amabili abophayo nebhangqa elilodwa ku-sulfur (AX₂E), ngakho imolekyuli iyi-bent. Ama-dipole amabili e-S–O akhomba ngokwengxenye ohlangothini olufanayo, isamba sawo asiyi-zero, futhi i-SO₂ ihlukanisiwe. I-SO₃ inama-electron e-valence angu-6 + 3(6) = 24 nama-domain amathathu abophayo angenabhangqa elilodwa ku-sulfur (AX₃), ngakho iyi-trigonal planar. Ama-dipole amathathu alinganayo ahlukene ngo-120° ahlangana abe yi-zero, futhi i-SO₃ ayihlukanisiwe nakuba yonke imibopho kuyo ihlukanisiwe.

Amaphutha avamile esimo nobuhlobo

Amaphutha amaningi aqhamuka ekweqeni isakhiwo se-Lewis noma ekufundeni umdweba ophuma ephepheni sengathi usimo sangempela. Umkhuba osheshayo uyawabamba: dweba isakhiwo se-Lewis, bala ama-domain ku-athomu eyisisekelo, qamba ijiyomethri ye-electron-domain, susa amabhangqa amodwa ukuqamba isimo semolekyuli, bese wengeza ama-dipole ezibopho ngobukhulu obuthathu.

Imodeli engokoqobo noma umdweba onyakanyakiswe ngokucophelela ukusiza esinyathelweni sokugcina. Uma ungayiphendula imolekyuli ukuze i-dipole yesibopho esisodwa ingabi nomlingani okhomba ngakolunye uhlangothi, imolekyuli ihlukanisiwe. Uma isibopho ngasinye silinganiswa yisibopho esifanayo ohlangothini oluphambene, noma isethi elinganayo efana nezibopho ezintathu ku-120°, ayihlukanisiwe.

• Ukuqamba ijiyomethri ye-electron-domain lapho umbuzo ubuza isimo semolekyuli. Ama-domain amanzi ayi-tetrahedral; isimo sawo siyi-bent.
• Ukukhohlwa amabhangqa amodwa ku-athomu eyisisekelo, okuphendula i-NH₃ ibe yimolekyuli ye-trigonal planar ngephutha.
• Ukubala isibopho esiphindwe kabili noma kathathu njenge-domain ezimbili noma ezintathu.
• Ukuphetha ngokuthi imolekyuli ihlukanisiwe ngoba izibopho zayo zihlukanisiwe, ngaphandle kokuhlola ukuthi ama-dipole ayakhansela yini.
• Ukwahlulela ukulingana emdwebeni oyisicaba. I-CH₂Cl₂ ibonakala ilinganayo ephepheni kodwa iyi-tetrahedral enezinhlobo ezimbili ezihlukene zezibopho, ngakho ihlukanisiwe.
• Ukubeka amabhangqa amodwa ezindaweni ze-axial ze-trigonal bipyramid, okunikeza isimo esingalungile se-SF₄, ClF₃ ne-XeF₂.