Qib kev paub txog cov qauv ntawm atoms thiab molecules nyob rau hauv lub xyoo pua puv 19 tsis tau tso cai piav qhia txog vim li cas atoms tsim muaj qee qhov sib txuas nrog lwm cov khoom. Tab sis cov tswv yim ntawm cov kws tshawb fawb tau ua ntej lawv lub sijhawm, thiab qhov tseem ceeb tseem tab tom kawm los ua ib qho ntawm cov hauv paus ntsiab lus ntawm chemistry.
Los ntawm keeb kwm ntawm lub tswv yim ntawm "valency of chemical element"
Edward Frankland, tus kws tshuaj Askiv zoo tshaj plaws ntawm lub xyoo pua 19th, tau qhia lo lus "kev cog lus" rau hauv kev tshawb fawb los piav txog cov txheej txheem ntawm kev sib cuam tshuam ntawm atoms nrog ib leeg. Tus kws tshawb fawb pom tias qee cov tshuaj lom neeg tsim cov tebchaw nrog tib tus lej ntawm lwm cov atoms. Piv txwv li, nitrogen txuas peb hydrogen atoms hauv ammonia molecule.
Nyob rau lub Tsib Hlis 1852, Frankland tau xav tias muaj qee qhov tshwj xeeb ntawm cov khoom siv tshuaj lom neeg uas lub atom tuaj yeem tsim nrog lwm cov khoom me me. Frankland siv cov kab lus "kev sib txuas lus" los piav txog dab tsi tom qab hu ua valency. British chemist txiav txim siab npaum li caschemical bonds tsim atoms ntawm tus kheej cov ntsiab lus paub nyob rau hauv nruab nrab ntawm lub xyoo pua 19th. Frankland txoj hauj lwm yog ib qho tseem ceeb pab rau niaj hnub structural chemistry.
Kev tsim tus cwj pwm
German chemist F. A. Kekule tau ua pov thawj hauv xyoo 1857 tias carbon yog tetrabasic. Hauv nws qhov yooj yim tshaj plaws - methane - muaj kev sib raug zoo nrog 4 hydrogen atoms. Tus kws tshawb fawb tau siv lo lus "basicity" los qhia txog cov khoom ntawm cov ntsiab lus txhawm rau txhawm rau txheeb xyuas tus lej ntawm lwm cov khoom. Nyob rau hauv Russia, cov ntaub ntawv ntawm tus qauv ntawm cov teeb meem tau systematized los ntawm A. M. Butlerov (1861). Txoj kev xav ntawm kev sib raug zoo ntawm cov tshuaj tau txais kev txhim kho ntxiv ua tsaug rau cov lus qhuab qhia ntawm kev hloov pauv nyob rau hauv cov khoom ntawm cov khoom. Nws tus kws sau ntawv yog lwm tus kws tshaj lij Lavxias teb sab, D. I. Mendeleev. Nws tau ua pov thawj tias qhov muaj txiaj ntsig ntawm cov tshuaj lom neeg hauv cov tebchaw thiab lwm yam khoom yog vim txoj haujlwm lawv nyob hauv lub sijhawm.
duab sawv cev ntawm valence thiab chemical bond
Qhov muaj peev xwm ntawm qhov pom kev sawv cev ntawm cov molecules yog ib qho ntawm qhov zoo ntawm qhov kev xav ntawm valency. Thawj cov qauv tau tshwm sim nyob rau xyoo 1860, thiab txij li xyoo 1864 cov qauv qauv tau siv, uas yog cov voj voog nrog cov cim tshuaj nyob rau hauv. Nyob nruab nrab ntawm cov cim ntawm atoms, ib tug khiav ceev qhia txog tshuaj lom neeg daim ntawv cog lus, thiab tus naj npawb ntawm cov kab no yog sib npaug rau tus nqi ntawm valency. Nyob rau hauv tib lub xyoo, thawj pob-thiab-loj qauv tau ua (saib daim duab ntawm sab laug). Nyob rau hauv 1866, Kekule tau npaj ib qho kev kos duab stereochemical ntawm lub atom.carbon nyob rau hauv daim ntawv ntawm tetrahedron, uas nws muaj nyob rau hauv nws phau ntawv Organic Chemistry.
Qhov muaj txiaj ntsig ntawm cov tshuaj lom neeg thiab qhov tshwm sim ntawm cov ntawv cog lus tau kawm los ntawm G. Lewis, uas luam tawm nws cov haujlwm hauv xyoo 1923 tom qab tshawb pom cov hluav taws xob. Qhov no yog lub npe ntawm qhov tsawg tshaj plaws tsis zoo nqi hais tias yog ib feem ntawm lub plhaub ntawm atoms. Nyob rau hauv nws phau ntawv, Lewis siv cov dots nyob ib ncig ntawm plaub sab ntawm cov tshuaj lub cim cim los sawv cev valence electrons.
Valency rau hydrogen thiab oxygen
Ua ntej tsim cov txheej txheem ntu ntu, qhov muaj txiaj ntsig ntawm cov tshuaj lom neeg hauv cov tebchaw feem ntau yog piv nrog cov atoms uas nws paub. Hydrogen thiab oxygen tau raug xaiv ua qauv. Lwm yam tshuaj lom neeg nyiam lossis hloov qee tus lej ntawm H thiab O atoms.
Hauv txoj kev no, cov khoom raug txiav txim siab hauv cov tebchaw nrog monovalent hydrogen (valence ntawm lub ntsiab thib ob yog qhia los ntawm Roman tus lej):
- HCl - chlorine (I):
- H2O - oxygen (II);
- NH3 - nitrogen (III);
- CH4 - carbon (IV).
In oxides K2O, CO, N2O3, SiO 2, SO3 txiav txim siab cov pa oxygen valency ntawm cov hlau thiab cov hlau tsis muaj hlau los ntawm kev ua ob npaug ntawm cov O atoms ntxiv. Cov txiaj ntsig hauv qab no tau txais: K (I), C (II), N (III), Si (IV), S (VI).
Yuav ua li cas txiav txim siab qhov muaj txiaj ntsig ntawm cov tshuaj lom neeg
Muaj ib txwm muaj nyob rau hauv kev tsim cov tshuaj tiv thaiv uas muaj cov khoom siv hluav taws xobkhub niam txiv:
- Hydrogen valency yog I.
- Usual oxygen valency - II.
- Rau cov ntsiab lus tsis yog hlau, qhov qis tshaj plaws tuaj yeem txiav txim siab los ntawm cov qauv 8 - tus naj npawb ntawm pawg uas lawv nyob hauv lub sijhawm. Qhov siab tshaj plaws, yog tias ua tau, yog txiav txim los ntawm pab pawg naj npawb.
- Rau cov ntsiab lus ntawm cov pab pawg thib ob, qhov siab tshaj plaws tau muaj txiaj ntsig yog tib yam li lawv cov pab pawg hauv lub sijhawm.
Kev txiav txim siab ntawm qhov valence ntawm cov tshuaj lom neeg raws li cov qauv ntawm cov khoom sib xyaw yog ua los ntawm kev siv cov algorithm hauv qab no:
- Sau tus nqi paub rau ib qho ntawm cov ntsiab lus saum toj sau npe tshuaj. Piv txwv li, hauv Mn2O7 cov pa oxygen yog II.
- Xaiv tag nrho tus nqi, uas koj yuav tsum tau muab cov valence los ntawm tus naj npawb ntawm atoms ntawm tib cov tshuaj nyob rau hauv lub molecule: 27=14.
- Kev txiav txim siab valence ntawm lub caij thib ob uas nws tsis paub. Faib tus nqi tau nyob rau hauv kauj ruam 2 los ntawm tus naj npawb ntawm Mn atoms nyob rau hauv lub molecule.
- 14: 2=7. Qhov siab ntawm manganese hauv nws cov oxide ntau dua yog VII.
Nco ntsoov thiab hloov pauv tau
Valence qhov tseem ceeb rau hydrogen thiab oxygen sib txawv. Piv txwv li, sulfur nyob rau hauv lub compound H2S yog bivalent, thiab nyob rau hauv cov mis SO3 nws yog hexavalent. Carbon tsim monoxide CO thiab dioxide CO 2 nrog oxygen. Hauv thawj qhov sib xyaw, qhov muaj txiaj ntsig ntawm C yog II, thiab hauv qhov thib ob, IV. Tib tus nqi hauv methane CH4.
MuajCov ntsiab lus nthuav tawm tsis tas li, tab sis qhov sib txawv ntawm qhov sib txawv, piv txwv li, phosphorus, nitrogen, sulfur. Kev tshawb nrhiav qhov laj thawj tseem ceeb ntawm qhov tshwm sim no tau coj mus rau qhov tshwm sim ntawm cov tshuaj tiv thaiv kev tshawb xav, cov tswv yim hais txog lub plhaub valence ntawm electrons, thiab molecular orbitals. Lub hav zoov ntawm qhov sib txawv ntawm cov khoom qub tau piav qhia los ntawm qhov pom ntawm cov qauv ntawm atoms thiab molecules.
Ntawm tswv yim txog kev zoo
Txhua lub atoms muaj cov nucleus zoo nyob ib puag ncig los ntawm cov hluav taws xob tsis zoo. Lub plhaub sab nrauv uas lawv tsim tsis tiav. Cov qauv ua tiav yog qhov ruaj khov tshaj plaws, muaj 8 electrons (ib qho octet). Qhov tshwm sim ntawm cov tshuaj tiv thaiv vim muaj cov khoom siv hluav taws xob sib xyaw ua rau muaj lub zog muaj txiaj ntsig zoo ntawm atoms.
Txoj cai rau kev tsim cov khoom sib txuas yog ua tiav ntawm lub plhaub los ntawm kev lees txais cov khoom siv hluav taws xob lossis muab cov khoom tsis sib xws - nyob ntawm seb cov txheej txheem twg yooj yim dua. Yog tias ib qho atom muab kev tsim cov tshuaj tiv thaiv cov khoom tsis zoo uas tsis muaj ib khub, ces nws tsim tau ntau daim ntawv cog lus raws li nws muaj cov khoom siv hluav taws xob tsis sib xws. Raws li cov tswv yim niaj hnub no, qhov valence ntawm atoms ntawm cov tshuaj lom neeg yog lub peev xwm los tsim ib tug xov tooj ntawm covalent bonds. Piv txwv li, hauv hydrogen sulfide molecule H 2 S, sulfur tau txais valency II (–), txij li txhua lub atom koom nrog kev tsim ntawm ob lub electron. Lub cim "–" qhia qhov kev nyiam ntawm ib khub electron mus rau ib qho khoom siv hluav taws xob ntau dua. Rau qhov tsawg dua electronegative, "+" yog ntxiv rau tus nqi valency.
Nrog rau tus neeg txais kev pabcuam, cov khoom siv hluav taws xob ntawm ib lub caij thiab dawb valence orbitals ntawm lwm lub caij koom nrog hauv cov txheej txheem.
Txoj kev vam meej ntawm tus qauv ntawm lub atom
Cia peb saib cov piv txwv ntawm cov pa roj carbon thiab oxygen, qhov valence ntawm cov tshuaj nyob ntawm seb cov qauv ntawm cov khoom. Lub sij hawm lub sij hawm muab lub tswv yim ntawm cov yam ntxwv tseem ceeb ntawm cov pa roj carbon atom:
- tshuaj kos npe - C;
- tus lej - 6;
- core nqi - +6;
- protons hauv lub nucleus - 6;
- electrons - 6, suav nrog 4 sab nraud, ntawm uas 2 tsim ib khub, 2 tsis muaj khub.
Yog tias cov pa roj carbon atom hauv CO monoxide tsim ob daim ntawv cog lus, tsuas yog 6 qhov tsis zoo tuaj rau nws siv. Txhawm rau kom tau txais octet, nws yog ib qho tsim nyog uas cov khub tsim 4 qhov tsis zoo sab nraud. Carbon muaj valency IV (+) hauv dioxide thiab IV (–) hauv methane.
Tus lej ntawm cov pa oxygen yog 8, lub plhaub valence muaj rau lub tshuab hluav taws xob, 2 ntawm lawv tsis tsim ua khub thiab koom nrog kev sib raug zoo tshuaj thiab kev cuam tshuam nrog lwm cov atoms. Ib qho piv txwv oxygen valency yog II (–).
Valency thiab oxidation xeev
Ntau zaus nws yooj yim dua los siv lub tswv yim ntawm "oxidation state". Qhov no yog lub npe muab rau tus nqi ntawm ib qho atom uas nws yuav tau txais yog tias tag nrho cov kev sib txuas ntawm electrons raug xa mus rau ib lub caij uas muaj tus nqi siab dua ntawm electronegativity (EO). Tus lej oxidation hauv cov khoom yooj yim yogxoom. Qhov kos npe "–" ntxiv rau lub xeev oxidation ntawm EO ntau dua, cov cim "+" ntxiv rau qhov tsawg dua electronegative. Piv txwv li, rau cov hlau ntawm pawg tseem ceeb, oxidation xeev thiab ion tsub nqi yog ib yam, sib npaug rau pawg naj npawb nrog "+" kos npe. Feem ntau, valency thiab oxidation lub xeev ntawm atoms nyob rau hauv tib lub compound yog tus lej tib yam. Tsuas yog thaum sib cuam tshuam nrog ntau cov electronegative atoms, lub xeev oxidation yog qhov zoo, nrog cov ntsiab lus uas EO qis dua, nws yog qhov tsis zoo. Lub tswvyim ntawm "valency" feem ntau yog siv rau cov khoom ntawm cov qauv molecular xwb.
