Nkag Siab Txog Covalence thiab Piv Txwv
Pendahuluuan
Hauv kev tshuaj lom neeg, txoj kev uas cov atoms sib xyaw ua ke los tsim ib yam khoom feem ntau txiav txim siab txog cov yam ntxwv ntawm cov khoom ntawd. Ib lub tswv yim tseem ceeb uas piav qhia txog kev sib txuas ntawm cov atoms yog covalence. Covalent bonds (covalence) feem ntau pom muaj nyob rau hauv cov tshuaj uas muaj cov khoom tsis yog hlau, piv txwv li hauv dej (H₂O), carbon dioxide (CO₂), methane (CH₄), thiab ntau yam organic compounds uas yog lub hauv paus ntawm lub neej. Kev nkag siab txog lub ntsiab lus ntawm covalence thiab cov piv txwv yuav pab peb nkag siab txog cov qauv molecular tsim li cas, vim li cas qee yam khoom muaj qee qhov kub npau npau, vim li cas qee cov tshuaj yooj yim yaj hauv dej, thiab cov tshuaj reactivity tshwm sim li cas.
Nkag Siab Txog Covalence
Covalence yog ib lub tswv yim ntsig txog kev tsim cov kev sib txuas ntawm covalent, uas yog cov kev sib txuas tshuaj uas tshwm sim thaum ob lub atoms sib koom ib khub electrons kom ua tiav kev ruaj khov. Feem ntau, cov atoms xav ua tiav qhov kev teeb tsa electron ruaj khov zoo li cov pa roj tsw qab (octet txoj cai), uas muaj 8 electrons hauv lawv lub plhaub sab nraud tshaj plaws (txawm hais tias muaj qee qhov kev zam). Vim tias cov atoms tsis yog hlau feem ntau muaj cov electronegativities siab thiab "tsis yooj yim" poob electrons, txoj hauv kev zoo tshaj plaws los ua tiav kev ruaj khov yog los ntawm kev sib koom electrons, es tsis txhob muab lossis tau txais lawv tag nrho zoo li hauv cov ionic bonds.
Hauv lwm lo lus, thaum nyob rau hauv cov ionic bonds electrons raug xa mus los ntawm ib lub atom mus rau lwm lub, nyob rau hauv covalent bonds electrons raug sib koom. Cov electrons sib koom tsim ib khub electron bonding, uas "khi" ob lub nuclei atomic ua ke los tsim ib lub molecule lossis covalent bond.
Vim li cas Covalent Bonds tshwm sim?
Cov kev sib txuas ntawm covalent tshwm sim vim yog lub zog uas tsav mus txog qhov qis dua thiab ruaj khov dua. Thaum ob lub atoms mus txog ib leeg, lawv cov electrons valence tuaj yeem sib koom ua ke, ua rau nws zoo li txhua lub atom "muaj" ntau cov electrons txaus hauv nws lub plhaub sab nraud. Qhov no ua rau lub cev ruaj khov dua li thaum cov atoms sawv ib leeg.
Piv txwv li, ib lub hydrogen atom (H) muaj ib lub electron thiab xav kom ruaj khov zoo li helium (He) nrog ob lub electron. Ob lub hydrogen atoms tuaj yeem sib koom ib khub electron, tsim ib lub molecule H₂. Txhua lub H₂ atom tam sim no "xav" zoo li nws muaj ob lub electron hauv nws lub plhaub thawj zaug, yog li ua tiav kev ruaj khov.
Hom Covalent Bonds
Covalent bonds tuaj yeem paub qhov txawv raws li tus naj npawb ntawm cov electron pairs sib koom thiab kuj raws li qhov sib txawv ntawm electronegativity ntawm cov atoms.
1. Raws li tus naj npawb ntawm cov khub hluav taws xob sib koom
1. Ib daim ntawv cog lus covalent: sib koom 1 khub electrons.
Piv txwv li: H—H hauv H₂, lossis C—H hauv CH₄.
2. Ob chav covalent daim ntawv cog lus: sib koom 2 khub ntawm electrons.
Piv txwv li: O=O hauv O₂, lossis C=O hauv CO₂.
3. Peb lub pob sib koom ua ke: sib koom 3 khub ntawm cov electrons.
Piv txwv li: N≡N ntawm N₂.
Qhov ntau cov electron khub sib koom ua ke, qhov muaj zog ntawm kev sib txuas thiab qhov luv dua ntawm qhov deb ntawm cov atoms.
2. Raws li polarity
1. Cov ntawv cog lus tsis yog polar
Tshwm sim thaum ob lub atoms muaj tib yam lossis zoo sib xws electronegativities, yog li ntawd cov electron khub tau sib koom ua ke sib npaug.
Piv txwv li: H₂, O₂, N₂, Cl₂.
2. Cov ntawv cog lus sib txuas Polar
Qhov no tshwm sim thaum qhov sib txawv ntawm electronegativity tseem ceeb txaus uas cov electron khub raug rub mus rau ib qho ntawm cov atoms. Qhov no ua rau muaj cov nqi ib nrab (δ⁺ thiab δ⁻).
Piv txwv li: H—Cl hauv HCl, O—H hauv H₂O.
Nws yog ib qho tseem ceeb kom paub qhov txawv tias qhov sib txuas polar tsis tas txhais tau tias lub molecule yog polar; qhov polarity ntawm lub molecule kuj tseem cuam tshuam los ntawm cov duab ntawm lub molecule (geometry).
Piv txwv ntawm Covalence hauv Cov Compounds Txhua Hnub
Nov yog qee cov piv txwv uas yooj yim nrhiav tau hauv lub neej txhua hnub:
1. Dej (H₂O)
Dej yog ib qho piv txwv tseem ceeb ntawm cov tshuaj uas muaj cov polar covalent bonds. Lub atom oxygen muaj electronegative ntau dua li hydrogen, yog li ntawd, ob lub atom no nyiam oxygen ntau dua. Qhov no muab cov dej cov yam ntxwv tshwj xeeb xws li nws lub peev xwm los yaj ntau yam khoom, kev nruj ntawm qhov chaw siab, thiab qhov kub siab dua piv rau lwm cov molecule me me.
Hauv H₂O, muaj ob lub polar O—H bonds. Tsis tas li ntawd, qhov "bent" (tsis yog linear) zoo li ntawm cov dej molecules txhais tau tias lawv cov dipole moments tsis rho tawm ib leeg, yog li ntawd cov dej molecules tag nrho yog polar.
2. Cov pa roj carbon dioxide (CO₂)
CO₂ muaj ob txoj kev sib txuas ntawm C thiab O (O=C=O). Txoj kev sib txuas C=O yog polar, tab sis CO₂ yog linear, yog li nws ob lub dipole moments tshem tawm ib leeg. Yog li ntawd, lub molecule CO₂ yog nonpolar kiag li. Qhov no yog ib qho laj thawj vim li cas CO₂ yaj tsawg dua hauv dej dua li cov tshuaj polar ntshiab, txawm hais tias nws tseem tuaj yeem teb rau carbonic acid nyob rau hauv qee qhov xwm txheej.
3. Methane (CH₄)
Methane yog ib qho organic compound yooj yim uas muaj cov bonds covalent ntawm C thiab H. Feem ntau, CH₄ yog nonpolar vim nws cov duab yog tetrahedral symmetrical thiab qhov sib txawv ntawm electronegativity ntawm C thiab H tsis loj dhau. Methane yog cov khoom tseem ceeb ntawm cov roj ntuj thiab siv dav ua roj.
4. Pa oxygen (O₂) thiab Nitrogen (N₂)
O₂ muaj ob txoj kev sib txuas (O=O), thaum N₂ muaj peb txoj kev sib txuas (N≡N). Txoj kev sib txuas peb zaug hauv N₂ muaj zog heev, ua rau nitrogen tsis tshua muaj zog (tsis yooj yim ua rau muaj teeb meem) nyob rau hauv cov xwm txheej ib txwm muaj. Qhov no yog vim li cas nitrogen thiaj li tswj hwm lub ntiaj teb huab cua tab sis tsis yooj yim ua rau muaj teeb meem yam tsis muaj cov xwm txheej tshwj xeeb lossis kev pab los ntawm cov tshuaj catalyst.
5. Hydrogen chloride (HCl)
HCl yog ib qho piv txwv ntawm cov polar covalent bond. Chlorine (Cl) muaj electronegative ntau dua li hydrogen, yog li nws cov electrons nyiam Cl ntau dua, ua rau muaj ib feem ntawm tus nqi. Thaum yaj hauv dej, HCl ionizes los ua H⁺ thiab Cl⁻, ua rau nws hu ua ib qho kua qaub muaj zog. Qhov no qhia tau hais tias ib qho compound tuaj yeem muaj covalent bond tab sis tsim cov ions hauv cov kua.
6. Ammonia (NH₃)
Ammonia muaj kev sib txuas ntawm N thiab H. Lub molecule NH₃ yog trigonal pyramidal hauv cov duab thiab yog polar. Ammonia yog siv dav hauv kev lag luam chiv, kev ntxuav, thiab ntau yam txheej txheem tshuaj lom neeg. Ammonia lub polarity tso cai rau nws cuam tshuam nrog dej zoo heev.
Cov Yam Ntxwv Dav Dav ntawm Covalent Compounds
Feem ntau, cov tshuaj sib xyaw ua ke muaj cov yam ntxwv hauv qab no (txawm hais tias muaj qee qhov kev zam):
1. Muaj ntau yam uas tsim los ntawm cov khoom uas tsis yog hlau.
2. Feem ntau muaj cov ntsiab lus yaj thiab kub qis dua li cov tshuaj ionic, tshwj xeeb tshaj yog rau cov molecule me me.
3. Cov tshuaj sib xyaw ua ke uas tsis yog polar feem ntau tsis yaj hauv dej, tab sis yaj tau hauv cov kuab tshuaj uas tsis yog polar.
4. Tsis txhob coj hluav taws xob thaum lub cev khov; qee yam tuaj yeem coj hluav taws xob yog tias ionized hauv cov kua (piv txwv li HCl hauv dej).
5. Pom muaj nyob rau hauv ntau cov organic compounds xws li hydrocarbons, alcohols, organic acids, thiab proteins.
Kev kaw
Covalence yog ib lub tswv yim tseem ceeb uas piav qhia txog yuav ua li cas cov atoms, tshwj xeeb tshaj yog cov uas tsis yog hlau, tsim cov kev sib txuas los ntawm kev sib koom cov khub electron. Covalent bonds tuaj yeem yog ib qho, ob npaug, lossis peb npaug, thiab tuaj yeem yog polar lossis nonpolar. Piv txwv yog paub zoo txog lub neej txhua hnub, xws li dej (H₂O), carbon dioxide (CO₂), methane (CH₄), oxygen (O₂), nitrogen (N₂), thiab hydrogen chloride (HCl). Los ntawm kev nkag siab txog kev txhais ntawm covalence thiab cov piv txwv, peb tuaj yeem yooj yim txuas cov qauv molecular nrog cov khoom siv lub cev thiab tshuaj ntawm cov khoom.
Yog tias koj xav tau, kuv tuaj yeem ntxiv ib qho kev tshawb fawb ntxiv ntawm tsab xov xwm (nrog kev sib tham txog Lewis cov qauv, txoj cai octet, thiab molecular geometry) lossis ib qho version yooj yim dua rau cov tub ntxhais kawm theem siab.
