Ukubopha kwamakhemikhali ne-electronegativity: kusuka emabhangqeni ahlanganyelwe kuya kuma-lattice e-ionic

Kungani isibopho sakheka: amandla uma eqhathaniswa nebanga

Ama-athomu amabili e-hydrogen akude komunye nomunye awasebenzisani. Njengoba esondelana, i-electron ngayinye iheheka kuzo zombili ama-nucleus, futhi amandla ayehla. Uma esondela nakakhulu, ama-nucleus amabili ayaxoshana kakhulu futhi amandla ayakhuphuka. Ubude besibopho yibanga elisezansi kwalo mgodi wamandla, 74 pm ku-H₂, futhi ukujula komgodi kungamandla esibopho, 436 kJ/mol ku-H–H kuTafula 7.2 le-OpenStax Chemistry 2e.

Isibopho ngasinye siwukulinganisela phakathi kokuheha nokuxoshana, ngakho ukwephula isibopho kuhlale kudinga amandla futhi ukusakha kuhlale kuwakhulula. Ukusabela kuyi-exothermic lapho izibopho ezakhiwe ziqine kakhulu sezizonke kunezibopho eziphukile.

I-electronegativity nesikali esisuka ku-covalent siye ku-ionic

I-electronegativity ilinganisa ukuthi i-athomu iwaheha kangakanani ama-electron ahlanganyelwe esibophweni. Isikali sika-Pauling yisona esivame kakhulu. Siyinombolo ebaliwe engenayunithi, hhayi isakhiwo esilinganisiwe. KuMfanekiso 7.6 we-OpenStax, i-fluorine iphezulu kakhulu ku-4.0, ilandelwa yi-oxygen ku-3.5 ne-nitrogen ne-chlorine ku-3.0, futhi izinsimbi zeqembu 1 ziphansi kakhulu, njenge-sodium ku-0.9. Amanani ayakhuphuka ngaphesheya kwesikhathi futhi ehle phansi eqenjini.

Umehluko u-ΔEN phakathi kwama-athomu amabili aboshiwe unikeza uhlobo lwesibopho olucishe lube njalo. I-OpenStax isebenzisa le mingcele yokuqondisa: ngaphansi kuka-0.4, i-nonpolar covalent; 0.4 kuya ku-1.8, i-polar covalent; ngaphezu kuka-1.8, i-ionic. I-athomu ene-electronegativity ephakeme iphethe ishaji engxenye engelihle, δ−.

Le mingcele iyiziqondiso ezinokuhlukile kwangempela. I-HF ino-ΔEN = 1.9 kodwa iyimolekyuli ye-covalent, kanti i-SiF₄, eno-ΔEN = 2.2 esibophweni ngasinye se-Si–F, iyigesi yamamolekyuli. Sebenzisa u-ΔEN ukuqhathanisa izibopho, hhayi ukuhlukanisa inhlanganisela ngokuqiniseka.

Isibonelo esisebenzile: ukuhlela izibopho eziyisithupha ngokuhlukaniswa kwazo

Hlela u-B–H, C–Br, N–O, P–Cl, Al–Cl no-K–Br kusuka kokuhlukaniswe kancane kuya kokuhlukaniswe kakhulu, usebenzisa amanani amadala ka-Pauling kuMfanekiso 7.6 we-OpenStax: H 2.1, B 2.0, C 2.5, N 3.0, O 3.5, Al 1.5, P 2.1, Cl 3.0, Br 2.8 no-K 0.8.

Imihlukano ingu-B–H 0.1, C–Br 0.3, N–O 0.5, P–Cl 0.9, Al–Cl 1.5 no-K–Br 2.0, okuwukuhlelwa. Imiphumela emibili iyabamangaza abafundi abaningi. Ku-B–H, i-hydrogen iwumkhawulo ongelihle, ngoba i-boron ine-electronegativity ephansi kune-hydrogen. Futhi u-K–Br uwela ebangeni le-ionic, okuhambisana nokuthi i-potassium bromide iyinto eqinile ye-ionic, kanti u-Al–Cl uhlala eduze nesiqongo sebanga le-polar covalent; i-aluminum chloride ichazwa njenge-ionic kwezinye izigaba futhi njengeyamamolekyuli kwezinye.

Ama-dipole moment nephesenti lohlamvu lwe-ionic

Isibopho esihlukanisiwe sine-dipole moment μ = Qr, usayizi weshaji ehlukanisiwe uphindaphindwe ngebanga phakathi kwamashaji. Ama-dipole moment ngokuvamile anikezwa ngama-debye: 1 D = 3.336 × 10⁻³⁰ C·m. Uma ishaji ephelele ye-electron, 1.602 × 10⁻¹⁹ C, ibisuswa ibanga elingu-1 Å, i-dipole moment ibizoba ngu-4.803 D. Ukuqhathanisa u-μ olinganisiwe naleli nani le-ionic ngokuphelele kunikeza iphesenti elilinganiselwe lohlamvu lwe-ionic, (μ olinganisiwe / μ we-ionic ngokuphelele) × 100.

Isibonelo esisebenzile 1. I-NIST Chemistry WebBook ibhala, ku-H³⁵Cl esigabeni segesi, u-μ = 1.1085 D nobude besibopho bokulingana obungu-1.27455 Å. I-H⁺Cl⁻ eyi-ionic ngokuphelele kulelo banga ibizoba no-μ = 4.803 D/Å × 1.27455 Å = 6.122 D. Iphesenti lohlamvu lwe-ionic lingu-1.1085/6.122 × 100 = 18.1%. Ku-HF, ngamanani e-WebBook μ = 1.82618 D no-r = 0.91680 Å, inani le-ionic ngokuphelele lingu-4.404 D futhi uhlamvu lwe-ionic lungu-41.5%.

Ukuhlelwa kuvumelana no-ΔEN (0.9 ku-HCl, 1.9 ku-HF), kodwa izinombolo zikhombisa ukuthi ngisho no-ΔEN omkhulu ukude kangakanani nokudluliswa okuphelele kweshaji. I-HF iseduze nohlangothi lwe-covalent kunalokho u-ΔEN wayo yedwa akusikiselayo.

Amandla e-lattice nomthetho ka-Coulomb

Into eqinile ye-ionic ihlanganiswa ukuheha phakathi kwayo yonke i-cation nayo yonke i-anion ku-crystal. Amandla ayo e-lattice angamandla adingekayo ukuhlukanisa i-mole eyodwa yento eqinile ibe ama-ayoni egesi. I-OpenStax iwachaza njengamahle, kodwa ezinye izincwadi zisebenzisa inqubo ephambene futhi zinikeze amanani angemahle, ngakho hlola umthetho wophawu kuqala.

Ngokomthetho ka-Coulomb, ukuheha kuyakhula ngomkhiqizo wamashaji ama-ayoni futhi kwehle njengoba ibanga phakathi kwama-ayoni likhula. Ishaji ngokuvamile iyona ebusayo. Isigaba 7.5 se-OpenStax sibhala i-LiF ku-1023 kJ/mol ne-MgO, ama-ayoni ayo aphethe amashaji angu-2+ no-2−, ku-3900 kJ/mol, cishe kukhulu ngokuphindwe kane. Usayizi ubaluleka ngokulandelayo: i-MgF₂ ingu-2957 kJ/mol kanti i-MgI₂ ingu-2327 kJ/mol, ngoba i-ayoni ye-iodide enkulu igcina amashaji ekude kakhulu.

Isibonelo esisebenzile: umjikelezo we-Born–Haber we-sodium chloride

Amandla e-lattice awakwazi ukulinganiswa ngqo, ngakho atholakala ngomjikelezo womthetho ka-Hess. Yakha i-NaCl(s) ezakhini zayo ngomzila ongaqondile onamasinyathelo onke angalinganiswa, bese ufuna ukuthi lowo mzila unikeze isamba esifanayo nokusabela kokwakheka okuqondile.

Isibonelo esisebenzile 2. Sebenzisa la masinyathelo. Yenza i-sodium ibe umhwamuko, Na(s) → Na(g): +107.5 kJ/mol, u-ΔH°f we-Na(g) ovela kuSithasiselo G se-OpenStax. Yenza ama-athomu e-chlorine, ½ Cl₂(g) → Cl(g): +121.3 kJ/mol, u-ΔH°f we-Cl(g). Yenza i-sodium ibe yi-ayoni, Na(g) → Na⁺(g) + e⁻: +495.8 kJ/mol, kusuka enanini le-NIST elingu-5.1391 eV. Engeza i-electron ku-chlorine, Cl(g) + e⁻ → Cl⁻(g): −348.6 kJ/mol, kusuka ku-electron affinity engu-3.6131 eV ku-NIST Chemistry WebBook. Ekugcineni, u-Na⁺(g) + Cl⁻(g) → NaCl(s) ukhulula amandla e-lattice, U.

Ukusabela kukonke ngu-Na(s) + ½ Cl₂(g) → NaCl(s), no-ΔH°f = −411.2 kJ/mol. Ngakho 107.5 + 121.3 + 495.8 − 348.6 − U = −411.2, okunikeza U = 787.2 kJ/mol. Qaphela ukuthi i-ionization idinga amandla amaningi kunalawo i-electron affinity ewabuyisayo. Ngaphandle kwamandla amakhulu e-lattice, ukwakha i-NaCl ezakhini zayo bekungeke kube yi-exothermic. Amandla e-lattice ashicilelwe e-NaCl ahluka ngamaphesenti ambalwa ngokwedatha nendlela esetshenzisiwe (i-OpenStax icaphuna u-769 kJ), ngakho qhathanisa izinkambiso kunezinombolo zokugcina.

Ukulinganisela i-enthalpy yokusabela ngamandla ezibopho

Ekusabeleni kwesigaba segesi, ungalinganisela u-ΔH ngokubala izibopho: ΔH ≈ Σ(amandla ezibopho eziphukile) − Σ(amandla ezibopho ezakhiwe). Amandla ezibopho abhalwe etafuleni ayizilinganiso zamamolekyuli amaningi, ngakho umphumela uwukulinganisela nje futhi ungaphambuka enanini elivela kuma-enthalpy okwakheka ngamashumi ama-kilojoule.

Isibonelo esisebenzile 3. Linganisela u-ΔH ka-C₂H₄(g) + H₂(g) → C₂H₆(g). Izibopho ezine ze-C–H ze-ethylene ziyasinda, ngakho zinganake. Eziphukile: i-C=C eyodwa (611 kJ/mol) ne-H–H eyodwa (436 kJ/mol), 1047 kJ sezizonke. Ezakhiwe: i-C–C eyodwa (345 kJ/mol) nezintsha ezimbili ze-C–H (2 × 415 kJ/mol), 1175 kJ sezizonke. ΔH ≈ 1047 − 1175 = −128 kJ. Inani le-enthalpy yokwakheka, elivela kuSithasiselo G, lingu-−84.0 − 52.4 = −136.4 kJ. Ukulinganisela kunophawu olulungile futhi kungaphakathi kuka-6% cishe.

Imibono eyiphutha ngokubopha okufanele uyigweme

Amaphutha amaningi avela ekuthatheni iziqondiso ezilinganiselwe njengemithetho eqondile noma ekuxubeni imithetho yezimpawu. Lawa ngamavame kakhulu.

• Ukuthatha u-ΔEN = 1.8 njengomugqa obukhali phakathi kwe-covalent ne-ionic. Isikali siyaqhubeka, futhi izinhlanganisela ezifana ne-HF ne-SiF₄ ziphula umthetho.
• Ukudida i-electronegativity ne-electron affinity. I-electron affinity ingamandla alinganisiwe e-athomu yegesi; i-electronegativity ichaza i-athomu esesibophweni.
• Ukucabanga ukuthi i-athomu ene-electronegativity ephakeme ihlala iyi-nonmetal obungayilindela. Hlola itafula: ezibophweni ze-B–H ne-Si–H, i-hydrogen iwumkhawulo ongelihle.
• Ukuphendula ifomula yamandla ezibopho. Iyizibopho eziphukile ukususa izibopho ezakhiwe, ukulandelana okuphambene nefomula ye-enthalpy yokwakheka.
• Ukuxuba imithetho yezimpawu zamandla e-lattice ngaphakathi komjikelezo owodwa we-Born–Haber.
• Ukubala isibopho esiphindwe kabili njengezibopho ezimbili ezingazodwa. Isibopho se-C=C (611 kJ/mol) sibuthaka kunezibopho ezimbili ze-C–C (690 kJ/mol).