Cov pawg ntawm cov molecules, zoo li cov huab hwm coj ntawm atoms, tsawg heev. Yog li ntawd, rau lawv cov kev xam, kev sib piv nrog ib tug atomic mass unit yog siv. Tus txheeb ze molecular hnyav ntawm ib tug compound yog ib tug lub cev kom muaj nuj nqis uas yog sib npaug zos rau qhov sib piv ntawm qhov loj ntawm ib tug compound molecule rau 1/12 ntawm ib tug carbon atom. Qhov ntsuas no qhia tau hais tias pes tsawg zaus qhov hnyav ntawm tag nrho cov molecule tshaj 1/12 ntawm qhov hnyav ntawm ib qho me me ntawm cov pa roj carbon monoxide thiab, zoo li txhua tus nqi txheeb ze, tsis muaj qhov ntev thiab yog cim los ntawm lub cim Mr.
Mr(compounds)=m(compound molecules) / 1/12 m(C). Txawm li cas los xij, hauv kev xyaum, siv cov txheej txheem sib txawv rau kev suav cov nqi no. Raws li nws, tus txheeb ze molecular hnyav yog sib npaug rau tag nrho cov nqi ntawm cov txheeb ze atomic masses (Ar) ntawm tag nrho cov tshuaj uas tsim ib tug muab compound, coj mus rau hauv tus account tus naj npawb ntawm elementary hais ntawm txhua lub caij, i.e. schematically sau tau zoo li no:
Mr(B1xC1y)=xAr(B1) +yAr(C1).
Yuav kom txiav txim siab tus nqi no kom raug, koj yuav tsum:
- paub cov tshuaj formula ntawm ib yam khoom;
- raug txiav txim Ar hauv lub rooj ntawm D. I. Mendeleev (yog li, yog tias tus lej tom qab tus lej lej yog sib npaug lossis ntau dua 5, ces ib qho ntxiv thaum sib npaug rau tag nrho tus lej: piv txwv li Ar (Li)=6, 941, rau kev suav siv tus lej uas yog 7, thiab yog tias tus lej tsawg dua 5, ces cia li nws yog: Ar (K)=39, 098, i.e. take 39).
- thaum xam Mr, tsis txhob hnov qab coj mus rau hauv tus account tus naj npawb ntawm atoms, i.e. indexes ntawm cov ntsiab lus nyob rau hauv cov qauv koom.
Nyob qhov hnyav molecular, cov qauv ntawm uas yog qhia schematically saum toj no, siv rau complex compounds. Vim hais tias los xam tus nqi no rau cov khoom yooj yim, nws yog txaus los txiav txim siab tsuas yog cov txheeb ze atomic loj raws li lub sij hawm lub sij hawm thiab, yog hais tias tsim nyog, muab faib los ntawm tus naj npawb ntawm elementary hais. Piv txwv li: Mr(P)=Ar (P)=31 thiab Mr(N2)=2 Ar (N)=214=18.
Cia peb xav txog lwm qhov piv txwv thiab nrhiav seb dab tsi yog qhov txheeb ze molecular hnyav ntawm dej - ib yam khoom nyuaj. Cov mis empirical ntawm cov tshuaj no yog H 2 O, i.e. Nws muaj 2 hydrogen atoms thiab 1 oxygen atom. Yog li ntawd, qhov kev daws teeb meem zoo li no:
Mr (H2O)=2Ar(H)+ Ar(O)=21+16=18
Yuav ua kom luv, tshem tawm cov lus qhia. Daim duab no qhia tau tias Mr yog 18 npaug ntau dua 1/12 ntawm qhov loj ntawm cov pa roj carbon monoxide. Ib yam li ntawd, qhov txheeb ze molecular hnyav ntawm ib qho tshuaj lom neeg yog txiav txim siab, yog tias nws paub txog cov mis empirical. Tab sis kuj, siv tus nqi no, nws muaj peev xwm rov qab tau qhov zoo thiab qhov muaj pes tsawg leeg ntawm cov khoom tsis paub, los tsim cov ntsiab lus ntawm tus kheej nuclides. Nyob rau hauv kev xyaum, lub cev thiab tshuaj txoj kev yog siv los txiav txim Mr ntawm ib yam khoom, xws li distillation, huab hwm coj spectrometry, roj chromatography, thiab lwm yam. Txhawm rau txiav txim siab qhov ntsuas no rau cov khoom siv polymers, txoj hauv kev yog siv los ntawm kev sib koom ua ke ntawm kev daws teeb meem (lawv txiav txim siab tus lej ntawm ob daim ntawv cog lus, pab pawg ua haujlwm, viscosity, muaj peev xwm tawg lub teeb).
Yog li, qhov sib txheeb molecular hnyav yog tus yam ntxwv ntawm txhua yam khoom thiab yuav yog tus kheej rau nws. Tus nqi no yog txiav txim siab rau ob qho tib si yooj yim thiab complex compounds, inorganic thiab organic. Nws qhov kev ua tau zoo yog qhov tseem ceeb tshwj xeeb hauv kev kawm thiab kev sib txuas ntawm cov polymers, cov khoom uas yuav nyob ntawm qhov ntsuas qhov hnyav molecular.
