Gaya antarmolekul dan bukti pelarut
Diperkenalkan| English | Makna |
|---|---|
| London forces | Gaya London |
| dipole/ˈdaɪpəʊl/ | dipol |
| hydrogen bonding/ˈhaɪdrədʒn ˈbɒndɪŋ/ | ikatan hidrogen |
| solubility/ˌsɒljuːˈbɪlɪti/ | kelarutan |
Why can a smaller molecule boil later?
- Ethanol can boil at a higher temperature than a similar-size alkane. A molecular formula alone does not show all the attractions.
- Predict which attractions are present before comparing the energy needed to separate molecules.
Build the attraction model
- All molecules have London forces 伦敦力 from instantaneous and induced dipoles 偶极. Polar molecules also have permanent dipole attractions.
- Hydrogen bonding 氢键 needs H bonded to N, O or F and a suitable lone pair on a neighbouring molecule.
Zat murni manakah yang dapat membentuk ikatan hidrogen dengan molekulnya sendiri?
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Metanol memiliki donor O–H dan pasangan elektron bebas oksigen. Eter tidak memiliki donor H yang sesuai; metana tidak memiliki keduanya.
Sebutkan atraksi yang melibatkan H terikat pada N, O, atau F dan pasangan elektron bebas tetangga yang sesuai.
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Ikatan hidrogen adalah atraksi antarmolekul, berbeda dari ikatan kovalen ke H tersebut.
Explain the boiling evidence
- Longer alkane chains usually have stronger London forces. Branching can reduce contact between isomers with the same electron count.
- Ethanol also hydrogen-bonds. Boiling overcomes attractions between molecules; it does not break all their internal covalent bonds.
Compare pentane with its compact branched isomer. Both have the same formula; the branched isomer usually boils at a lower temperature because intermolecular contact is reduced.
Semua zat molekuler memiliki gaya London.
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Awan elektron mereka dapat mengembangkan dipol sesaat yang menginduksi dipol pada tetangga.
Test a solvent prediction
- Water hydrates ions and hydrogen-bonds with small alcohols. A longer non-polar carbon chain usually lowers an alcohol’s water solubility 溶解度.
- An ether can accept hydrogen bonds from water but lacks an O–H donor for a pure-ether hydrogen-bond network.
Mengapa halogenoalkana dapat bersifat polar namun sukar larut dalam air?
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Kelarutan bergantung pada keseimbangan antara ikatan yang diputus dan terbentuk, bukan hanya pada satu ikutan polar.
Check the model limits
- Ice has an open hydrogen-bonded arrangement and lower density than liquid water near the melting point. Its molecules are not larger.
- A polar C–X bond does not alone ensure water solubility. New attractions must compensate for those broken in the solvent and solute.
“Boiling ethanol breaks its O–H covalent bonds” is false. The change mainly separates intact molecules by overcoming intermolecular attractions.
Identify particles, attractions and the physical change before explaining a temperature or solubility trend.
Manakah dua pernyataan yang menjelaskan es mengapung dekat titik lelehnya?
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Susunan terbuka menyebarkan molekul lebih jauh, menurunkan densitas. Molekul air individu mempertahankan identitasnya.