Sigma vs pi Bonds
Raws li tau hais los ntawm American chemist G. N. Lewis, atoms ruaj khov thaum lawv muaj yim electrons hauv lawv lub plhaub valence. Feem ntau ntawm cov atoms muaj tsawg tshaj li yim electrons nyob rau hauv lawv valence shells (tshwj tsis yog cov noble gases nyob rau hauv pab pawg neeg 18 ntawm lub periodic rooj); yog li ntawd, lawv tsis ruaj khov. Cov atoms no zoo li ua rau ib leeg ua kom ruaj khov. Yog li, txhua lub atom tuaj yeem ua tiav cov roj hluav taws xob hluav taws xob zoo. Qhov no tuaj yeem ua tiav los ntawm kev tsim cov ionic bonds, covalent bonds lossis metallic bonds. Ntawm cov no, covalent bonding yog tshwj xeeb. Tsis zoo li lwm cov tshuaj sib txuas, hauv covalent bonding muaj peev xwm ua tau ntau yam kev sib txuas ntawm ob lub atoms. Thaum ob lub atoms zoo sib xws los yog tsawg heev electronegativity sib txawv, lawv hnov qab ua ke thiab tsim ib daim ntawv cog lus los ntawm kev sib koom electrons. Thaum tus naj npawb ntawm kev sib koom electrons ntau tshaj ib qho ntawm txhua lub atom, ntau daim ntawv cog lus tshwm sim. Los ntawm kev xam daim ntawv cog lus, tus naj npawb ntawm covalent bonds ntawm ob lub atoms hauv ib lub molecule tuaj yeem txiav txim siab. Ntau daim ntawv cog lus yog tsim nyob rau hauv ob txoj kev. Peb hu lawv sigma daim ntawv cog lus thiab pi daim ntawv cog lus.
Sigma Bond
Lub cim σ yog siv los qhia txog daim ntawv cog lus. Ib daim ntawv cog lus yog tsim thaum ob lub tshuab hluav taws xob sib koom ntawm ob lub atoms uas zoo sib xws lossis qis electronegativity sib txawv. Ob lub atoms tuaj yeem yog tib hom lossis ntau hom. Piv txwv li, thaum tib atoms koom ua ke los tsim cov molecules xws li Cl2, H2, los yog P4., txhua lub atom raug khi rau lwm tus los ntawm ib daim ntawv cog lus. Methane molecule (CH4) muaj ib qho kev sib cog lus ntawm ob hom khoom (carbon thiab hydrogen atoms). Tsis tas li ntawd, methane yog ib qho piv txwv rau cov molecule uas muaj covalent bonds ntawm atoms uas tsis tshua muaj electronegativity sib txawv. Ib leeg covalent bonds kuj muaj npe hu ua sigma bonds. Sigma daim ntawv cog lus yog covalent bonds muaj zog tshaj plaws. Lawv yog tsim los ntawm ob lub atoms los ntawm kev sib txuas atomic orbitals. Lub taub hau rau lub taub hau sib tshooj tuaj yeem pom thaum ua sigma daim ntawv cog lus. Piv txwv li hauv ethane thaum ob qhov sib npaug sp3 hybridized molecules yog linearly overlapped, C-C sigma daim ntawv cog lus yog tsim. Tsis tas li, C-H sigma daim ntawv cog lus yog tsim los ntawm cov kab sib tshooj ntawm ib qho sp 3hybridized orbital los ntawm carbon thiab s orbital los ntawm hydrogen. Cov pab pawg sib koom ua ke tsuas yog los ntawm daim ntawv cog lus sigma muaj peev xwm ua kom muaj kev sib hloov ntawm qhov kev sib raug zoo nrog kev hwm rau ib leeg. Qhov kev sib hloov no tso cai rau lub molecule kom muaj cov qauv sib txawv.
pib Bond
Tsab ntawv Greek π yog siv los qhia txog pi bonds. Qhov no kuj yog covalent chemical bond, uas feem ntau tsim ntawm p orbitals. Thaum ob lub p orbitals tom qab sib tshooj pi daim ntawv cog lus tsim. Thaum qhov sib tshooj no tshwm sim, ob lub lobes ntawm p orbital cuam tshuam nrog ob lub lobes ntawm lwm lub p orbital thiab lub dav hlau nodal yog tshwm sim ntawm ob lub atomic nuclei. Thaum muaj ntau daim ntawv cog lus ntawm atoms, thawj daim ntawv cog lus yog sigma daim ntawv cog lus thiab qhov thib ob thiab peb daim ntawv cog lus yog pi bonds.
Qhov txawv ntawm Sigma Bond thiab pi Bond yog dab tsi?
• Sigma bonds yog tsim los ntawm lub taub hau mus rau lub taub hau overlapping ntawm orbitals, whereas pi bonds yog tsim los ntawm lateral overlapping.
• Sigma bonds muaj zog dua pi bonds.
• Sigma bonds tuaj yeem tsim los ntawm ob qho tib si s thiab p orbitals whereas pi bonds feem ntau tsim ntawm p thiab d orbitals.
• Covalent daim ntawv cog lus ib leeg ntawm atoms yog sigma bonds. Thaum muaj ntau daim ntawv cog lus ntawm atoms, pi bonds tuaj yeem pom.
• pi bonds ua rau cov molecules unsaturated.
• Sigma daim ntawv cog lus pub dawb kev sib hloov ntawm atoms whereas pi bonds txwv qhov kev sib hloov dawb.
