Qhov sib txawv tseem ceeb ntawm molecular orbital theory thiab valence bond theory yog tias molecular orbital theory piav txog kev tsim molecular orbital, whereas valence bond theory piav txog atomic orbitals.
Ntau cov molecules muaj cov tshuaj lom neeg thiab lub cev sib txawv dua li cov atoms uas koom ua ke los tsim cov molecules. Yuav kom nkag siab txog qhov sib txawv ntawm cov khoom atomic thiab molecular, nws yog ib qho tsim nyog yuav tsum nkag siab txog kev tsim cov tshuaj lom neeg ntawm ntau lub atoms los ua ib qho molecule. Tam sim no, peb siv ob quantum mechanical theories los piav txog covalent daim ntawv cog lus thiab cov qauv hluav taws xob ntawm cov molecules. Cov no yog valence bond theory thiab molecular orbital theory.
Dab tsi yog Molecular Orbital Theory?
Nyob rau hauv molecules, electrons nyob rau hauv molecular orbitals, tab sis lawv cov duab txawv, thiab lawv muaj feem xyuam nrog ntau tshaj ib tug atomic nuclei. Lub molecular orbital txoj kev xav yog kev piav qhia ntawm molecules raws li molecular orbitals.
Peb tuaj yeem tau txais cov haujlwm nthwv dej piav qhia txog lub molecular orbital los ntawm kev sib xyaw ua ke ntawm atomic orbitals. Ib daim ntawv cog lus orbital thaum ob lub atomic orbitals cuam tshuam rau tib theem (kev sib cuam tshuam). Thaum lawv cuam tshuam tawm ntawm theem (kev cuam tshuam kev puas tsuaj), kev tiv thaiv kev sib txuas lus los ntawm. Yog li ntawd, muaj kev sib raug zoo thiab kev tiv thaiv kev sib txuas lus rau txhua qhov kev sib cuam tshuam suborbital. Bonding orbitals muaj lub zog qis, thiab cov khoom siv hluav taws xob muaj feem ntau nyob hauv cov. Anti-bonding orbitals yog lub zog siab, thiab thaum tag nrho cov kev sib koom ua ke orbitals tau ntim, cov electrons mus thiab sau cov kev tiv thaiv kev sib txuas.
Valence Bond Theory yog dab tsi?
Valence daim ntawv cog lus txoj kev xav yog ua raws li kev cog lus hauv cheeb tsam, uas xav tias cov hluav taws xob hauv cov molecule tuav atomic orbitals ntawm tus kheej atoms. Piv txwv li, hauv kev tsim ntawm H 2 molecule, ob lub hydrogen atoms sib tshooj lawv 1s orbitals. Los ntawm kev sib tshooj ntawm ob lub orbitals, lawv sib koom ib cheeb tsam hauv qhov chaw. Thaum pib, thaum ob lub atoms nyob deb, tsis muaj kev cuam tshuam ntawm lawv. Yog li ntawd, lub zog muaj peev xwm yog xoom.
Raws li lub atoms mus rau ib leeg, txhua lub electron yog attracted los ntawm lub nucleus nyob rau hauv lwm lub atom, thiab tib lub sij hawm, electrons repel ib leeg, ib yam li cov nuclei. Thaum lub atoms tseem sib cais, qhov attraction yog ntau dua li lub repulsion, yog li lub peev xwm ntawm lub zog txo. Lub ntsiab lus ntawm lub peev xwm lub zog mus txog qhov tsawg kawg nkaus tus nqi, lub kaw lus nyob ruaj khov. Qhov no tshwm sim thaum ob lub hydrogen atoms tuaj ua ke thiab tsim cov molecule.
Daim duab 01: Tsim Pi Bond
Txawm li cas los xij, lub tswv yim sib tshooj no tsuas yog piav qhia yooj yim molecules xws li H2, F2, HF, thiab lwm yam. Qhov kev xav no tsis piav qhia molecules zoo li CH4 Txawm li cas los xij, qhov teeb meem no tuaj yeem daws tau los ntawm kev sib txuas cov kev xav no nrog cov kev tshawb xav hybrid orbital. Hybridization yog kev sib xyaw ntawm ob qhov tsis sib xws atomic orbitals. Piv txwv li, hauv CH4, C muaj plaub hybridized sp3 orbitals overlapping nrog s orbitals ntawm txhua H.
Qhov txawv ntawm Molecular Orbital Theory thiab Valence Bond Theory yog dab tsi?
Tam sim no, peb siv ob lub quantum mechanical theories los piav txog covalent daim ntawv cog lus thiab cov qauv hluav taws xob ntawm cov molecules. Cov no yog Valence bond theory thiab molecular orbital theory. Qhov sib txawv tseem ceeb ntawm molecular orbital theory thiab valence bond theory yog tias molecular orbital theory piav qhia txog kev tsim cov molecular orbital, hos valence bond theory piav txog atomic orbitals. Ntxiv mus, valence bond txoj kev xav tsuas yog siv tau rau diatomic molecules, thiab tsis yog rau polyatomic molecules. Txawm li cas los xij, peb tuaj yeem siv txoj kev xav molecular orbital rau ib qho molecule.
Summary – Molecular Orbital Theory vs Valence Bond Theory
Valence bond theory thiab molecular orbital theory yog ob lub quantum mechanical theories uas piav txog covalent daim ntawv cog lus thiab cov qauv hluav taws xob ntawm cov molecules. Qhov sib txawv tseem ceeb ntawm molecular orbital theory thiab valence bond theory yog tias molecular orbital theory piav qhia txog kev tsim cov molecular orbital, hos valence bond theory piav txog atomic orbitals.
