Amandla phakathi kwamamolekyuli: indawo yokubila, ingcindezi yomhwamuko nokuncibilika

Ukuheha phakathi kwamamolekyuli, hhayi izibopho ezingaphakathi kwawo

Izibopho ze-covalent zibamba ama-athomu emolekyulini ndawonye. Amandla phakathi kwamamolekyuli (ama-IMF) ayinto ebuthaka kakhulu yokuheha phakathi kwamamolekyuli ahlukene, futhi yilokho okufanele kunqotshwe lapho uketshezi lubila noma into eqinile incibilika. Lapho amanzi ebila, igesi eyakhekayo isenziwe ngamamolekyuli e-H₂O; azikho izibopho ze-O–H ezephukayo. Ukuheha kuphela phakathi kwamamolekyuli aseduze kuphazanyiswa.

Ngoba la mandla alawula ukuthi amamolekyuli anamathelana kangakanani, alawula isethi yezakhiwo zenyama ndawonye. Ama-IMF aqinile ngokuvamile asho indawo yokubila ephakeme, i-enthalpy ephakeme yomhwamuko, ingcindezi yomhwamuko ephansi ezingeni lokushisa elithile, futhi kaningi ukunamathela okukhulu nokungcindezeleka kwendawo. Uma ungawalungisa ama-IMF, ngokuvamile ungawalungisa wonke lokhu ngesikhathi esisodwa.

Amandla e-London dispersion kuzo zonke izinto

Amandla e-dispersion avela ngoba ukusatshalaliswa kwama-electron kuyashintshashintsha. Nganoma yisiphi isikhathi ama-electron emolekyulini angaba ngalinganiyo kancane, adale i-dipole yesikhashana ebangela i-dipole efanayo kumakhelwane. Ayabhekana isikhashana, futhi iphethini iphinda kuso sonke uketshezi. Yonke i-athomu nemolekyuli ihlangabezana namandla e-dispersion, ihlukanisiwe noma cha.

Amandla e-dispersion ancike ku-polarizability, okusho ukuthi ifu lama-electron lingaguqulwa kalula kangakanani. Amamolekyuli amakhulu anama-electron amaningi aguquleka kalula, ngakho amandla e-dispersion ngokuvamile akhula ngesisindo se-molar emndenini wezinhlanganisela ezifanayo. Isimo nacho sibalulekile: amamolekyuli amade, anwetshiwe ane-surface eningi ethintana nomakhelwane kuneyahlangene, enamagatsha efomula efanayo, ngakho ahehana kakhulu.

Ungawenyeleli amandla e-dispersion. Kumamolekyuli amakhulu kaningi kuyisabelo esikhulu kakhulu sokuheha okuphelele, ngisho nalapho imolekyuli ihlukanisiwe.

Ukuheha kwe-dipole–dipole nokubopha kwe-hydrogen

Amamolekyuli ahlukanisiwe anama-dipole aqhubekayo, ngakho koketshezi athambekele ukuzibeka nesiphetho esihle ngokwengxenye semolekyuli eyodwa eduze nesiphetho esingelihle ngokwengxenye seyinye. Lokhu kuheha kwe-dipole–dipole kwengeza emandleni e-dispersion ahlala ekhona. Ukunquma ukuthi imolekyuli ihlukanisiwe yini kudinga zombili ubuhlobo bezibopho nesimo sayo.

Ukubopha kwe-hydrogen kuyindlela eqinile ikakhulu yokuheha kwe-dipole–dipole. Kudinga i-athomu ye-hydrogen ebophelelwe nge-covalent ku-nitrogen, oxygen noma fluorine (umnikeli) nebhangqa elilodwa ku-athomu eseduze ye-N, O noma F (umamukeli). Isibopho esihlukanisiwe kakhulu se-N–H, O–H noma F–H sishiya i-athomu encane ye-hydrogen nokushaji okukhulu okuhle ngokwengxenye okungasondela eduze nebhangqa elilodwa lomamukeli.

Imolekyuli ingaba ngumamukeli ngaphandle kokuba ngumnikeli. I-acetone, (CH₃)₂CO, inebhangqa elilodwa ku-oxygen kodwa wonke ama-hydrogen ayo abophelelwe ku-carbon, ngakho amamolekyuli e-acetone awakwazi ukubophana nge-hydrogen. Nokho, angamukela izibopho ze-hydrogen ezivela emanzini, okuyisizathu esisodwa sokuthi i-acetone ixube namanzi ngazo zonke izilinganiso.

Amandla e-ion–dipole nokuncibilika kwezinto eziqinile ze-ayoni

Lapho into eqinile ye-ayoni incibilika emanzini, i-ayoni ngayinye izungezwa amamolekyuli amanzi abheke kuyo: iziphetho ze-oxygen ezingezinhle ngokwengxenye zibheke ama-cation, futhi iziphetho ze-hydrogen ezinhle ngokwengxenye zibheke ama-anion. Lokhu kuheha kwe-ion–dipole kukhulula amandla anele ukulinganisa okuningi kwamandla adingekayo ukuhlukanisa ama-ayoni ekristalu. Ukuheha kuqine kuma-ayoni anamashaji aphezulu nosayizi omncane.

Amandla e-ion–dipole achaza ukuthi kungani i-potassium bromide incibilika kalula emanzini kodwa cishe ayincibiliki ku-hexane, engenayo i-dipole yokuheha ama-ayoni. Umthetho ojwayelekile othi "okufanayo kuncibilikisa okufanayo" ufingqa lokhu: izinto zincibilika kangcono ezincibilikisini ezinamandla phakathi kwamamolekyuli afana nawazo. I-iodine, imolekyuli engahlukaniswanga, incibilika kahle ku-hexane, lapho amandla e-dispersion phakathi kwe-solute nesincibilikisi enganyelisa lawo angaphakathi kwento ngayinye ecwebile.

Isibonelo esisebenzile: oketshezi oluthathu olunesisindo se-molar esicishe sifane

Hlela i-butane (CH₃CH₂CH₂CH₃), i-acetone ((CH₃)₂CO) ne-1-propanol (CH₃CH₂CH₂OH) ngendawo yokubila. Qala ngokuqhathanisa izisindo ze-molar, usebenzisa izisindo ze-athomu ezijwayelekile ze-IUPAC eziyiswe emadesimalini amabili (H 1.01, C 12.01, O 16.00 g/mol). I-butane, C₄H₁₀: 4(12.01) + 10(1.01) = 58.14 g/mol. I-acetone, C₃H₆O: 3(12.01) + 6(1.01) + 16.00 = 58.09 g/mol. I-1-propanol, C₃H₈O: 3(12.01) + 8(1.01) + 16.00 = 60.11 g/mol. Izisindo ziyahluka ngaphansi kuka-4%, ngakho amandla e-dispersion kufanele afane kakhulu futhi umehluko uzovela ekuhlukaniseni.

Okulandelayo hlukanisa amandla. I-butane iqukethe izibopho ze-C–C ne-C–H kuphela futhi cishe ayihlukanisiwe, ngakho inamandla e-dispersion kuphela. I-acetone inesibopho esihlukanisiwe se-C=O ekuhlelweni kwe-trigonal planar okungakhanseli, ngakho yengeza amandla e-dipole–dipole, kodwa ayinaso isibopho se-O–H futhi ayikwazi ukunikela ngezibopho ze-hydrogen. I-1-propanol inamaqembu e-O–H, ngakho yengeza ukubopha kwe-hydrogen. Isibikezelo ngu-butane < acetone < 1-propanol.

I-NIST Chemistry WebBook ibhala izindawo zokubila ezijwayelekile cishe ezingu-273 K (0 °C) ye-butane, 329.3 K (56.2 °C) ye-acetone no-370.3 K (97.2 °C) ye-1-propanol, ngokuguqula nge-T(°C) = T(K) − 273.15. Ukulandelana kuyavumelana nesibikezelo. Ukucabanga okufanayo kuhlela ingcindezi yomhwamuko ezingeni lokushisa lasekamelweni ngokulandelana okuphambene: i-butane iyigesi ku-25 °C, i-acetone ihwamuka ngokushesha, futhi i-1-propanol ihwamuka kancane.

Isibonelo esisebenzile: lapho usayizi wemolekyuli unqoba i-dipole

Manje qhathanisa i-diethyl ether ((C₂H₅)₂O), i-1-butanol (CH₃CH₂CH₂CH₂OH) ne-hexane (C₆H₁₄). I-diethyl ether ne-1-butanol ziyi-isomer, zombili C₄H₁₀O: 4(12.01) + 10(1.01) + 16.00 = 74.14 g/mol. I-hexane isindayo: 6(12.01) + 14(1.01) = 86.20 g/mol. I-diethyl ether ihlukanisiwe kodwa ayinaso isibopho se-O–H, i-1-butanol ingabopha nge-hydrogen, futhi i-hexane ayihlukanisiwe.

Phakathi kwama-isomer amabili, ukubopha kwe-hydrogen kunquma: i-1-butanol kufanele ibile ngaphezulu kakhulu kune-diethyl ether. I-hexane iyicala elifundisayo. Impikiswano yobuhlobo kuphela ibingayibeka yokugcina, kodwa i-hexane inkulu, inama-electron amaningi futhi iyiketango elinwetshiwe, ngakho amandla ayo e-dispersion makhulu kune-dispersion ye-ether kanye nokuheha kwayo okubuthaka kwe-dipole–dipole.

Amanani e-NIST aqinisekisa lokhu: i-diethyl ether 307.7 K (34.6 °C), i-hexane 341.9 K (68.8 °C) ne-1-butanol 390.6 K (cishe 117 °C). Isifundo ukuthi ukuqhathanisa ubuhlobo kuphephe kakhulu phakathi kwamamolekyuli osayizi ofanayo. Lapho osayizi behluka kakhulu, cabanga nge-dispersion kuqala bese ubuza ukuthi i-dipole noma ukubopha kwe-hydrogen kuqine ngokwanele ukuyiphendula yini. Ukuncibilika kulandela amandla nako: i-hexane cishe ayincibiliki emanzini, kanti i-1-butanol, engabopha nge-hydrogen namanzi, iyancibilika ngokwengxenye.

Amaphutha okugwema lapho kuqhathaniswa amandla phakathi kwamamolekyuli

Ngaphambi kokuhlela, bhala wonke amandla into ngayinye ekhona esikhundleni sokuqinile kuphela, futhi uqaphele izisindo ze-molar. Lokhu kuvimbela iphutha elivame kakhulu, lokuqhathanisa amalebula kuphela afana nokuthi "ihlukanisiwe" ne-"ayihlukanisiwe" ngenkathi unganaki usayizi.

Amaphutha angezansi avela kaningi ezincazelweni zendawo yokubila nokuncibilika.

• Ukusho ukuthi ukubila kwephula izibopho ze-covalent. Ukubila kuhlukanisa amamolekyuli; amamolekyuli ahlala ephelele.
• Ukusho ukubopha kwe-hydrogen kunoma yimuphi umolekyuli oqukethe i-hydrogen. I-hydrogen kufanele ibophelelwe ku-N, O noma F.
• Ukuthatha izinto ezingahlukanisiwe njengezingenawo amandla phakathi kwamamolekyuli. Zonke izinto zinamandla e-dispersion.
• Ukuhlela amamolekyuli osayizi ohluke kakhulu ngobuhlobo kuphela, njengoba isibonelo se-hexane sikhombisa.
• Ukuphendula inkambiso yengcindezi yomhwamuko. Ama-IMF aqinile asho ingcindezi yomhwamuko ephansi nendawo yokubila ephakeme.
• Ukuthatha "okufanayo kuncibilikisa okufanayo" njengomthetho kunokuba kube umthetho wesithupha. Ukuncibilika kuncike nakwi-entropy nasezingeni lokushisa.