Lub tswv yim ntawm kev sib cog lus tshuaj tsis muaj qhov tseem ceeb hauv ntau yam ntawm chemistry raws li kev tshawb fawb. Qhov no yog vim lub fact tias nws yog nrog nws cov kev pab uas ib tug neeg atoms muaj peev xwm ua ke mus rau hauv molecules, tsim txhua yam ntawm cov tshuaj, uas, nyob rau hauv lem, yog cov kev tshawb fawb tshuaj.
Ntau yam ntawm atoms thiab molecules yog txuam nrog kev tshwm sim ntawm ntau hom kev sib txuas ntawm lawv. Cov chav sib txawv ntawm cov molecules yog cov yam ntxwv ntawm lawv tus kheej cov yam ntxwv ntawm kev faib tawm ntawm cov hluav taws xob, thiab yog li lawv tus kheej hom kev sib cog lus.
Basic concepts
Cov tshuaj lom neeg yog ib txheej ntawm kev sib cuam tshuam uas ua rau kev sib txuas ntawm cov atoms los tsim cov khoom ruaj khov ntawm cov qauv ntau dua (molecules, ions, radicals), nrog rau cov khoom sib xyaw (pob zeb, iav, thiab lwm yam). Qhov xwm ntawm cov kev sib cuam tshuam no yog hluav taws xob hauv qhov xwm txheej, thiab lawv tshwm sim thaum lub sij hawm faib cov valence electrons nyob rau hauv mus txog atoms.
Valency feem ntau yog hu ua lub peev xwm ntawm ib lub atom los tsim ib tug lej ntawm cov ntawv cog lus nrog lwm cov atoms. Nyob rau hauv ionic tebchaw, tus naj npawb ntawm muab los yog txuas electrons yog coj raws li tus nqi ntawm valence. ATnyob rau hauv covalent tebchaw, nws yog sib npaug rau tus naj npawb ntawm cov electron khub.
Lub xeev oxidation tau nkag siab tias yog tus nqi them nqi uas tuaj yeem nyob ntawm lub atom yog tias tag nrho cov polar covalent bonds yog ionic.
Daim ntawv cog lus ntau yog tus naj npawb ntawm cov khoom siv hluav taws xob sib koom ntawm cov atoms.
Cov nyiaj tau txiav txim siab hauv ntau ceg ntawm chemistry tuaj yeem muab faib ua ob hom tshuaj tiv thaiv: cov uas ua rau tsim cov tshuaj tshiab (intramolecular), thiab cov uas tshwm sim ntawm cov molecules (intermolecular).
Cov yam ntxwv sib txuas lus yooj yim
Lub zog khi yog lub zog xav tau los rhuav tshem txhua daim ntawv cog lus uas twb muaj lawm hauv ib lub molecule. Nws kuj yog lub zog tso tawm thaum lub sij hawm tsim daim ntawv cog lus.
Daim ntawv cog lus ntev yog qhov kev ncua deb ntawm cov nuclei uas nyob ib sab ntawm atoms nyob rau hauv ib lub molecule, uas lub zog ntawm attraction thiab repulsion yog sib npaug.
Ob tus yam ntxwv ntawm cov tshuaj lom neeg ntawm cov atoms yog qhov ntsuas ntawm nws lub zog: qhov luv dua qhov ntev thiab lub zog ntau dua, qhov ruaj khov dua.
Lub kaum sab xis feem ntau hu ua lub kaum sab xis ntawm cov kab sawv cev dhau los ntawm kev sib txuas los ntawm cov nuclei ntawm atoms.
Txoj kev piav qhia txuas
Qhov ntau tshaj ob txoj hauv kev los piav qhia cov tshuaj lom neeg, qiv los ntawm quantum mechanics:
Txoj kev ntawm molecular orbitals. Nws suav hais tias yog ib qho molecule raws li ib txheej ntawm electrons thiab nuclei ntawm atoms, nrog rau txhua tus neeg electron txav mus rau hauv qhov kev txiav txim ntawm tag nrho lwm cov electrons thiab nuclei. Cov molecule muaj cov qauv orbital, thiab tag nrho nws cov electrons raug faib raws cov orbits. Tsis tas li ntawd, txoj kev no yog hu ua MO LCAO, uas sawv cev rau "molecular orbital - ib txoj kab sib txuas ntawm atomic orbitals".
Txoj kev ntawm valence bonds. Sawv cev ib molecule raws li ib tug system ntawm ob lub hauv paus molecular orbitals. Tsis tas li ntawd, txhua tus ntawm lawv sib raug rau ib daim ntawv cog lus ntawm ob lub atoms uas nyob ib sab hauv lub molecule. Cov txheej txheem yog ua raws li cov kev cai hauv qab no:
- Kev tsim cov tshuaj tiv thaiv yog ua los ntawm ib khub ntawm cov hluav taws xob nrog qhov sib txawv, uas nyob nruab nrab ntawm ob lub atoms. Cov tsim electron khub belongs rau ob atoms sib npaug.
- Tus naj npawb ntawm daim ntawv cog lus tsim los ntawm ib lossis lwm lub atom yog sib npaug rau cov xov tooj ntawm cov hluav taws xob tsis sib xws hauv av thiab lub xeev zoo siab.
- Yog cov khub electron tsis koom nrog hauv kev tsim daim ntawv cog lus, ces lawv hu ua ob leeg.
Electronegativity
Nws tuaj yeem txiav txim siab hom tshuaj lom neeg hauv cov tshuaj raws li qhov sib txawv ntawm cov txiaj ntsig electronegativity ntawm nws cov atoms. Electronegativity yog to taub raws li lub peev xwm ntawm atoms los nyiam cov khoom siv hluav taws xob (electron cloud), uas ua rau kev sib raug zoo polarization.
Muaj ntau txoj hauv kev los txiav txim qhov txiaj ntsig ntawm electronegativity ntawm cov tshuaj lom neeg. Txawm li cas los xij, feem ntau siv yog qhov ntsuas raws li cov ntaub ntawv ntsuas kub, uas tau thov rov qab rau xyoo 1932 los ntawm L. Pauling.
Qhov ntau dua qhov sib txawv ntawm cov electronegativity ntawm atoms, ntau tshaj nws cov ionicity. Ntawm qhov tsis sib xws, qhov sib npaug lossis ze electronegativity qhov tseem ceeb qhia txog covalent xwm ntawm daim ntawv cog lus. Hauv lwm lo lus, nws muaj peev xwm txiav txim siab seb cov tshuaj lom neeg twg tau pom nyob rau hauv ib qho kev ua lej. Ua li no, koj yuav tsum xam ΔX - qhov sib txawv ntawm electronegativity ntawm atoms raws li cov mis: ΔX=|X 1 -X 2 |.
- Yog ΔХ>1, 7, ces daim ntawv cog lus yog ionic.
- Yog 0.5≦ΔХ≦1.7, ces daim ntawv cog lus covalent yog polar.
- Yog ΔХ=0 lossis ze rau nws, ces daim ntawv cog lus yog covalent tsis-polar.
Ionic daim ntawv cog lus
Ionic yog xws li daim ntawv cog lus uas tshwm sim ntawm ions lossis vim qhov kev tshem tawm tag nrho ntawm ib khub electron los ntawm ib qho ntawm cov atoms. Hauv cov khoom, hom kev sib txuas ntawm cov tshuaj no yog ua los ntawm lub zog ntawm electrostatic attraction.
Ions yog them cov khoom tsim los ntawm atoms vim tias cov electrons tau txais lossis poob. Thaum lub atom txais electrons, nws kis tau tus nqi tsis zoo thiab dhau los ua anion. Yog hais tias ib qho atom pub valence electrons, nws dhau los ua ib qho txiaj ntsig zoo hu ua cation.
Nws yog yam ntxwv ntawm cov tebchaw tsim los ntawm kev sib cuam tshuam ntawm atoms ntawm cov hlau raug nrog atoms ntawm cov hlau tsis yog hlau. Lub ntsiab ntawm cov txheej txheem no yog kev cia siab ntawm atoms kom tau txais cov khoom siv hluav taws xob ruaj khov. Thiab rau qhov no, cov hlau raug thiab tsis yog hlau yuav tsum tau muab los yog txais tsuas yog 1-2 electrons,uas lawv ua tau yooj yim.
Lub tshuab ntawm kev tsim cov tshuaj ionic daim ntawv cog lus nyob rau hauv ib lub molecule yog ib txwm txiav txim siab siv cov piv txwv ntawm kev sib cuam tshuam ntawm sodium thiab chlorine. Alkali hlau atoms yooj yim pub ib qho hluav taws xob rub los ntawm halogen atom. Qhov tshwm sim yog Na+ cation thiab Cl- anion, uas tau tuav ua ke los ntawm electrostatic attraction.
Tsis muaj qhov zoo tshaj plaws ionic daim ntawv cog lus. Txawm hais tias nyob rau hauv cov tebchaw, uas feem ntau hu ua ionic, qhov kawg hloov ntawm electrons ntawm atom mus rau atom tsis tshwm sim. Cov tsim electron khub tseem nyob hauv kev siv ntau. Yog li ntawd, lawv tham txog qib ntawm ionicity ntawm covalent daim ntawv cog lus.
Ionic kev sib raug zoo yog tus yam ntxwv los ntawm ob lub ntsiab lus muaj feem cuam tshuam rau ib leeg:
- tsis yog kev taw qhia, piv txwv li qhov hluav taws xob nyob ib puag ncig ion muaj cov duab ntawm ib tus kheej;
- Unsaturation, piv txwv li tus naj npawb ntawm cov ions tawm tsam uas tuaj yeem muab tso rau ib puag ncig ion, txiav txim siab los ntawm lawv qhov loj me.
Covalent chemical bond
Daim ntawv cog lus tsim thaum cov huab cua hluav taws xob ntawm cov atoms tsis yog hlau sib tshooj, uas yog, nqa los ntawm ib qho khoom siv hluav taws xob, hu ua covalent daim ntawv cog lus. Tus naj npawb ntawm cov khub sib koom ntawm cov hluav taws xob txiav txim siab qhov sib npaug ntawm daim ntawv cog lus. Yog li, hydrogen atoms tau txuas los ntawm ib qho H··H daim ntawv cog lus, thiab cov pa oxygen atoms tsim ob daim ntawv cog lus O::O.
Nws muaj ob lub tswv yim rau nws tsim:
- Sib pauv - txhua lub atom sawv cev rau ib qho hluav taws xob rau kev tsim ntawm ib khub: A +B=A: B, thaum kev sib txuas nrog rau sab nraud atomic orbitals, ntawm ib qho hluav taws xob nyob.
- Tus neeg txais-tus neeg txais - los tsim ib daim ntawv cog lus, ib qho ntawm cov atoms (tus pub dawb) muab ib khub ntawm electrons, thiab qhov thib ob (acceptor) - lub orbital dawb rau nws qhov chaw: A +: B=A: B.
Txoj kev uas cov huab cua hluav taws xob sib tshooj thaum muaj cov khoom siv tshuaj lom neeg sib txawv kuj txawv.
- Direct. Cov huab sib tshooj cheeb tsam nyob ntawm ib txoj kab kev xav ncaj nraim txuas rau lub nuclei ntawm cov atoms xam. Hauv qhov no, σ-bonds raug tsim. Hom tshuaj lom neeg daim ntawv cog lus uas tshwm sim nyob rau hauv cov ntaub ntawv no yog nyob ntawm seb hom electron huab nyob rau hauv overlap: s-s, s-p, p-p, s-d los yog p-d σ-bonds. Hauv ib qho particle (molecule lossis ion), tsuas yog ib qho σ-bond tuaj yeem tshwm sim ntawm ob lub atoms nyob sib ze.
- Sib. Nws yog nqa tawm ntawm ob sab ntawm txoj kab txuas lub nuclei ntawm atoms. Qhov no yog li cas ib tug π-bond yog tsim, thiab nws ntau yam kuj ua tau: p-p, p-d, d-d. Sib cais los ntawm σ-bond, π-bond yeej tsis tsim; nws tuaj yeem ua rau hauv cov molecules uas muaj ntau yam (ob npaug thiab triple) daim ntawv cog lus.
Covalent bond properties
Lawv txiav txim siab cov tshuaj lom neeg thiab lub cev ntawm cov khoom sib txuas. Cov khoom tseem ceeb ntawm cov khoom siv tshuaj lom neeg hauv cov khoom yog nws cov kev taw qhia, polarity thiab polarizability, nrog rau saturation.
Qhov kev taw qhia ntawm daim ntawv cog lus txiav txim siab cov yam ntxwv ntawm cov molecularCov qauv ntawm cov khoom thiab cov duab geometric ntawm lawv cov molecules. Nws lub ntsiab lus nyob rau hauv qhov tseeb hais tias qhov zoo tshaj plaws sib tshooj ntawm electron huab yog ua tau nrog ib tug tej yam orientation nyob rau hauv qhov chaw. Cov kev xaiv rau kev tsim ntawm σ- thiab π-bonds twb tau txiav txim siab saum toj no.
Saturation yog to taub raws li lub peev xwm ntawm atoms los tsim ib tug xov tooj ntawm tshuaj bonds nyob rau hauv ib tug molecule. Tus naj npawb ntawm covalent bonds rau txhua lub atom yog txwv los ntawm tus naj npawb ntawm cov orbitals sab nraud.
Lub polarity ntawm daim ntawv cog lus yog nyob ntawm qhov sib txawv ntawm cov txiaj ntsig electronegativity ntawm cov atoms. Nws txiav txim siab qhov sib xws ntawm kev faib cov hluav taws xob ntawm cov nuclei ntawm atoms. Daim ntawv cog lus covalent ntawm lub hauv paus no tuaj yeem yog polar lossis tsis-polar.
- Yog tias tus khub electron sib npaug sib npaug ntawm txhua lub atoms thiab nyob ntawm tib qhov deb ntawm lawv cov nuclei, ces covalent daim ntawv cog lus tsis yog polar.
- Yog tias ob khub ntawm electrons hloov mus rau lub nucleus ntawm ib qho ntawm cov atoms, ces muaj covalent polar chemical bond tsim.
Polarizability yog qhia los ntawm kev hloov pauv ntawm daim ntawv cog lus electrons nyob rau hauv qhov kev txiav txim ntawm ib qho hluav taws xob sab nraud, uas tej zaum yuav yog rau lwm cov khoom, cov ntawv cog lus nyob sib ze hauv tib lub molecule, los yog los ntawm lwm qhov chaw ntawm electromagnetic teb. Yog li, daim ntawv cog lus cog lus nyob rau hauv lawv lub zog tuaj yeem hloov pauv nws qhov polarity.
Raws li hybridization ntawm orbitals nkag siab txog qhov kev hloov pauv hauv lawv cov ntaub ntawv hauv kev siv cov ntawv cog lus tshuaj. Qhov no yog qhov tsim nyog kom ua tiav qhov sib tshooj zoo tshaj plaws. Muaj cov nram qab no hom hybridization:
- sp3. Ib s- thiab peb p-orbitals ua plaub"hybrid" orbitals ntawm tib lub cev. Outwardly, nws zoo li lub tetrahedron nrog lub kaum sab xis ntawm lub axes ntawm 109 °.
- sp2. Ib lub s- thiab ob lub p-orbitals tsim ib daim duab peb sab tiaj tus nrog lub kaum sab xis ntawm lub axes ntawm 120 °.
- sp. Ib tug s- thiab ib tug p-orbital daim ntawv ob "hybrid" orbitals nrog lub kaum sab xis ntawm lawv axes ntawm 180 °.
Metal bond
Ib yam ntawm cov qauv ntawm cov hlau atoms yog lub vojvoog loj loj thiab muaj cov khoom siv hluav taws xob tsawg nyob rau sab nrauv orbitals. Yog li ntawd, nyob rau hauv xws li cov ntsiab lus tshuaj, kev sib raug zoo ntawm lub nucleus thiab valence electrons yog qhov tsis muaj zog thiab yooj yim tawg.
Hlau daim ntawv cog lus yog xws li kev sib cuam tshuam ntawm cov hlau atoms-ions, uas yog ua nrog kev pab los ntawm delocalized electrons.
Hauv cov khoom hlau, valence electrons tuaj yeem yooj yim tawm ntawm cov orbitals, nrog rau cov chaw tsis muaj nyob ntawm lawv. Yog li, nyob rau lub sijhawm sib txawv, tib cov khoom tuaj yeem yog atom thiab ion. Cov hluav taws xob tawg tawm ntawm lawv txav mus thoob plaws tag nrho cov ntim ntawm cov siv lead ua lattice thiab nqa tawm cov tshuaj lom neeg.
hom nyiaj no muaj qhov sib xws nrog ionic thiab covalent. Raws li rau ionic, ions yog tsim nyog rau lub hav zoov ntawm ib tug hlau daim ntawv cog lus. Tab sis yog hais tias rau kev siv ntawm electrostatic kev sib cuam tshuam nyob rau hauv thawj rooj plaub, cations thiab anions yuav tsum tau, ces nyob rau hauv lub thib ob, lub luag hauj lwm ntawm negatively them hais yog ua si los ntawm electrons. Yog tias peb sib piv cov hlau nplaum nrog covalent daim ntawv cog lus, qhov tsim ntawm ob qho tib si yuav tsum muaj cov khoom siv electrons. Txawm li cas los xij, hauvTsis zoo li daim ntawv cog lus tshuaj polar, lawv tsis nyob nruab nrab ntawm ob lub atoms, tab sis yog rau tag nrho cov hlau hais nyob rau hauv cov siv lead ua lattice.
Metallic bonds yog lub luag haujlwm rau cov khoom tshwj xeeb ntawm yuav luag txhua cov hlau:
- plasticity, tam sim no vim muaj peev xwm ntawm cov txheej txheem ntawm cov atoms nyob rau hauv cov siv lead ua lattice tuav los ntawm electron gas;
- metallic luster, uas tau pom vim qhov kev xav ntawm lub teeb rays los ntawm electrons (nyob rau hauv lub hmoov tsis muaj crystal lattice thiab, yog li ntawd, electrons txav raws nws);
- hluav taws xob conductivity, uas yog ua los ntawm cov kwj ntawm cov khoom them, thiab qhov no, cov hluav taws xob me me txav mus los ntawm cov hlau loj ions;
- thermal conductivity, soj ntsuam vim muaj peev xwm ntawm electrons hloov tshav kub.
Hydrogen bond
Hom tshuaj tiv thaiv no qee zaum hu ua qhov nruab nrab ntawm covalent thiab kev sib cuam tshuam. Yog tias hydrogen atom muaj kev sib raug zoo nrog ib qho ntawm cov khoom siv hluav taws xob muaj zog (xws li phosphorus, oxygen, chlorine, nitrogen), ces nws muaj peev xwm tsim tau ib daim ntawv cog lus ntxiv, hu ua hydrogen.
Nws yog qhov tsis muaj zog dua li txhua hom kev sib cog lus uas tau hais tseg saum toj no (lub zog tsis tshaj 40 kJ / mol), tab sis nws tsis tuaj yeem tsis quav ntsej. Yog vim li cas cov tshuaj hydrogen daim ntawv cog lus nyob rau hauv daim duab zoo li ib tug dotted kab.
Qhov tshwm sim ntawm daim ntawv cog lus hydrogen tuaj yeem ua tau vim yog tus neeg txais kev pabcuam electrostatic cuam tshuam tib lub sijhawm. Qhov sib txawv loj ntawm qhov muaj nqiselectronegativity ua rau cov tsos ntawm cov hluav taws xob ntau dhau ntawm cov atoms O, N, F thiab lwm yam, nrog rau nws qhov tsis muaj ntawm hydrogen atom. Nyob rau hauv qhov xwm txheej uas tsis muaj cov tshuaj tiv thaiv tam sim no ntawm cov atoms, cov zog txaus nyiam tau qhib yog tias lawv nyob ze txaus. Hauv qhov no, tus proton yog ib qho khoom siv hluav taws xob txais, thiab lub atom thib ob yog tus pub.
Hydrogen bonding tuaj yeem tshwm sim ob qho tib si ntawm cov molecules nyob sib ze, piv txwv li, dej, carboxylic acids, cawv, ammonia, thiab hauv cov molecule, piv txwv li, salicylic acid.
Lub xub ntiag ntawm hydrogen daim ntawv cog lus ntawm cov dej molecules piav qhia ntau yam ntawm nws lub cev lub cev:
- Qhov tseem ceeb ntawm nws lub peev xwm kub, dielectric tas li, boiling thiab melting cov ntsiab lus, raws li kev suav, yuav tsum tsawg dua qhov tseeb, uas tau piav qhia los ntawm kev sib txuas ntawm cov molecules thiab qhov yuav tsum tau siv. lub zog los rhuav tshem cov ntawv cog lus intermolecular hydrogen.
- Tsis zoo li lwm yam khoom, thaum qhov kub thiab txias, qhov ntim ntawm cov dej nce ntxiv. Qhov no yog vim lub fact tias cov molecules nyob rau hauv ib tug tej yam txoj hauj lwm nyob rau hauv lub crystal qauv ntawm cov dej khov thiab txav deb ntawm ib leeg los ntawm qhov ntev ntawm hydrogen daim ntawv cog lus.
Qhov kev sib txuas no ua lub luag haujlwm tshwj xeeb rau cov kab mob muaj sia, vim tias nws muaj nyob hauv cov protein molecules txiav txim siab lawv cov qauv tshwj xeeb, thiab yog li lawv cov khoom. Tsis tas li ntawd, nucleic acids, ua rau DNA ob lub helix, kuj tseem txuas nrog qhov tseeb ntawm hydrogen bonds.
Kev sib txuas lus hauv cov muaju
Feem ntau ntawm cov khib nyiab muaj cov iav siv lead ua - qhov tshwj xeebkev sib koom ua ke ntawm cov khoom uas tsim lawv. Nyob rau hauv cov ntaub ntawv no, peb-dimensional periodicity raug soj ntsuam, thiab atoms, molecules los yog ions nyob rau ntawm cov nodes, uas yog kev cob cog rua los ntawm kev xav txog kab. Nyob ntawm qhov xwm txheej ntawm cov khoom no thiab cov khoom sib txuas ntawm lawv, tag nrho cov qauv siv lead ua tau muab faib ua atomic, molecular, ionic thiab metallic.
Muaj cations thiab anions nyob rau hauv cov nodes ntawm ionic siv lead ua lattice. Ntxiv mus, txhua tus ntawm lawv yog nyob ib puag ncig los ntawm ib tug nruj me ntsis cov xov tooj ntawm ions nrog tsuas yog tus opposite nqi. Ib qho piv txwv yog sodium chloride (NaCl). Lawv zoo li muaj cov ntsiab lus melting siab thiab hardness vim lawv xav tau ntau lub zog tawg.
Molecules ntawm cov khoom tsim los ntawm covalent daim ntawv cog lus yog nyob rau ntawm cov nodes ntawm molecular crystal lattice (piv txwv li, I2). Lawv tau txuas nrog ib leeg los ntawm kev tsis muaj zog ntawm van der Waals, thiab yog li ntawd, cov qauv zoo li no yooj yim los rhuav tshem. Cov tebchaw no muaj cov ntsiab lus kub kub thiab melting tsawg.
Lub atomic siv lead ua lattice yog tsim los ntawm atoms ntawm cov tshuaj lom neeg muaj txiaj ntsig zoo. Lawv txuas nrog covalent bonds muaj zog, uas txhais tau hais tias cov khoom muaj cov ntsiab lus kub kub, cov ntsiab lus melting thiab siab hardness. Ib qho piv txwv yog pob zeb diamond.
Yog li, txhua hom kev sib cog lus pom hauv cov tshuaj muaj lawv tus kheej cov yam ntxwv, uas piav qhia qhov tsis sib xws ntawm kev sib cuam tshuam ntawm cov khoom hauv cov molecules thiab cov khoom. Cov khoom ntawm cov tebchaw nyob ntawm lawv. Lawv txiav txim siab tag nrho cov txheej txheem tshwm sim hauv ib puag ncig.
