Xidhiidhka kiimikaad iyo elektaroonaysiga: laga bilaabo lammaanayaal la wadaago ilaa shabagyo ayoon

Sababta xidhiidh u samaysmo: tamarta iyo masaafada

Laba atam hydrogen ah oo kala fog isma saameeyaan. Marka ay isu soo dhowaadaan, elektaroon kastaa wuxuu u soo jiitamaa labada nukliyeer, tamartuna way dhacdaa. Marka ay sii dhowaadaan, labada nukliyeer si xoog leh ayay isu riixaan, tamartuna way kacdaa. Dhererka xidhiidhku waa masaafada ku taal salka godkan tamarta, 74 pm ee H₂, qoto-dheerida godkuna waa tamarta xidhiidhka, 436 kJ/mol ee H–H ee OpenStax Chemistry 2e Shaxda 7.2.

Xidhiidh kastaa waa dheellitir u dhexeeya isjiidasho iyo is-riixid, sidaa darteed jebinta xidhiidh had iyo jeer tamar ayay ku kacdaa, samayntiisuna had iyo jeer tamar ayay sii deysaa. Falgal waa exothermic marka xidhiidhada la sameeyey ay guud ahaan ka xoog badan yihiin xidhiidhada la jebiyey.

Elektaroonaysiga iyo cabbirka covalent ilaa ayoon

Elektaroonaysigu wuxuu cabbiraa sida xoogga leh ee atam u soo jiito elektaroonnada la wadaago ee xidhiidh ku jira. Cabbirka Pauling ayaa ugu caansan. Waa tiro aan cutub lahayn oo la xisaabiyey, ma aha astaan la cabbiray. OpenStax Sawirka 7.6, fluorine ayaa ugu sarreeya 4.0, waxaana ku xiga oksijiin 3.5 iyo nitrogen iyo chlorine 3.0, biraha kooxda 1-na waa kuwa ugu hooseeya, sida sodium 0.9. Qiimayaashu way kordhaan marka xilliga la dhex maro wayna yaraadaan marka kooxda hoos loo raaco.

Farqiga ΔEN ee u dhexeeya laba atam oo xidhan wuxuu bixiyaa nooca xidhiidhka si qiyaas ah. OpenStax waxay isticmaashaa xadadkan hagitaanka ah: ka hooseeya 0.4, covalent aan laba-cirif ahayn; 0.4 ilaa 1.8, covalent laba-cirif ah; ka sarreeya 1.8, ayoon. Atamka elektaroonaysigiisu sarreeyo wuxuu sidaa dallacaadda taban ee qaybta ah, δ−.

Xadadku waa hagitaanno leh ka reebisyo dhab ah. HF wuxuu leeyahay ΔEN = 1.9 laakiin waa molekiyuul covalent ah, SiF₄-na, oo leh ΔEN = 2.2 xidhiidh kasta oo Si–F ah, waa gaas molekiyuul ah. ΔEN u isticmaal barbar dhigga xidhiidhada, ha u isticmaalin kala-saarista isku-dhis si hubaal ah.

Tusaale la xaliyey: kala horraysiinta lix xidhiidh sida ay laba-cirif u yihiin

Kala horraysii B–H, C–Br, N–O, P–Cl, Al–Cl iyo K–Br laga bilaabo kan ugu yar ilaa kan ugu badan laba-cirifnimada, adigoo isticmaalaya qiimayaasha Pauling ee hore ee OpenStax Sawirka 7.6: 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 iyo K 0.8.

Farqiyadu waa B–H 0.1, C–Br 0.3, N–O 0.5, P–Cl 0.9, Al–Cl 1.5 iyo K–Br 2.0, taasoo ah kala horraysiinta. Laba natiijo ayaa la yaaba arday badan. B–H, hydrogen waa cirifka taban, sababtoo ah boron elektaroonaysigiisu wuu ka yar yahay kan hydrogen. K–Br-na wuxuu ku dhacaa xadka ayoonka, taasoo waafaqsan in potassium bromide uu yahay walax adag oo ayoon ah, halka Al–Cl uu ku dhow yahay xagga sare ee xadka covalent-ka laba-cirifka ah; aluminum chloride waxaa lagu sharxaa ayoon xaaladaha qaarkood iyo molekiyuul kuwa kale.

Moment-yada laba-cirifka iyo boqolkiiba dabeecadda ayoonka

Xidhiidh laba-cirif ah wuxuu leeyahay moment laba-cirif μ = Qr, oo ah cabbirka dallacaadda kala go'day oo lagu dhuftay masaafada u dhexeysa dallacaadaha. Moment-yada laba-cirifka badanaa waxaa lagu bixiyaa debye: 1 D = 3.336 × 10⁻³⁰ C·m. Haddii dallacaadda buuxda ee elektaroon, 1.602 × 10⁻¹⁹ C, laga dhaqaajiyo 1 Å, moment-ka laba-cirifku wuxuu noqon lahaa 4.803 D. Barbar dhigga μ-da la cabbiray iyo qiimahan ayoonka buuxa ah wuxuu bixiyaa boqolkiiba qiyaas ah oo dabeecadda ayoonka ah, (μ la cabbiray / μ ayoon buuxa) × 100.

Tusaale la xaliyey 1. NIST Chemistry WebBook waxay u taxdaa H³⁵Cl ee heerka gaaska μ = 1.1085 D iyo dherer xidhiidh isu-dheellitir oo ah 1.27455 Å. H⁺Cl⁻ ayoon buuxa ah oo masaafadaas jira wuxuu yeelan lahaa μ = 4.803 D/Å × 1.27455 Å = 6.122 D. Boqolkiiba dabeecadda ayoonku waa 1.1085/6.122 × 100 = 18.1%. HF, oo leh qiimayaasha WebBook μ = 1.82618 D iyo r = 0.91680 Å, qiimaha ayoonka buuxa ahi waa 4.404 D, dabeecadda ayoonkuna waa 41.5%.

Kala horraysiintu waxay waafaqsan tahay ΔEN (0.9 ee HCl, 1.9 ee HF), laakiin tirooyinku waxay muujinayaan inta xataa ΔEN weyn uu u jiro wareejin buuxda oo dallacaad ah. HF wuxuu uga dhow yahay cirifka covalent-ka sida ΔEN-kiisa keligiis tilmaamo.

Tamarta shabagga iyo sharciga Coulomb

Walax adag oo ayoon ah waxaa isku haya isjiidashada u dhexeysa cation kasta iyo anion kasta oo kristaalka ku jira. Tamarta shabaggiisu waa tamarta loo baahan yahay in hal mool oo walaxda adag loo kala saaro ayoonno gaas ah. OpenStax waxay u qeexdaa mid togan, laakiin buugaagta qaarkood waxay isticmaalaan habraaca ka soo horjeeda oo bixiyaan qiimayaal taban, sidaa darteed marka hore hubi heshiiska calaamadda.

Marka loo eego sharciga Coulomb, isjiidashadu waxay la korodhaa wax-soo-saarka dallacaadaha ayoonnada wayna yaraataa marka masaafada u dhexeysa ayoonnadu korodho. Dallacaaddu badanaa ayaa ka adag. OpenStax Qaybta 7.5 waxay taxdaa LiF 1023 kJ/mol iyo MgO, oo ayoonnadiisu sidaan dallacaadaha 2+ iyo 2−, 3900 kJ/mol, ku dhawaad afar jibaar ka weyn. Cabbirku wuxuu muhiim yahay marka xigta: MgF₂ waa 2957 kJ/mol MgI₂-na waa 2327 kJ/mol, sababtoo ah ayoonka iodide ee ka weyn wuxuu dallacaadaha sii kala fogeeyaa.

Tusaale la xaliyey: wareegga Born–Haber ee sodium chloride

Tamarta shabagga si toos ah looma cabbiri karo, sidaa darteed waxaa lagu helaa wareeg sharciga Hess ah. Ka dhis NaCl(s) curiyayaashiisa waddo dadban oo tallaabooyinkeedu dhammaantood la cabbiri karo, kadibna shardi ka dhig in waddadaasi bixiso isla wadarta falgalka samaysanka tooska ah.

Tusaale la xaliyey 2. Isticmaal tallaabooyinkan. Sodium adag si toos ah gaas ugu beddel (sublimation), Na(s) → Na(g): +107.5 kJ/mol, ΔH°f ee Na(g) ee OpenStax Lifaaqa G. Samee atamyo chlorine ah, ½ Cl₂(g) → Cl(g): +121.3 kJ/mol, ΔH°f ee Cl(g). Ionaysii sodium, Na(g) → Na⁺(g) + e⁻: +495.8 kJ/mol, oo laga helay qiimaha NIST ee 5.1391 eV. Elektaroon ku dar chlorine, Cl(g) + e⁻ → Cl⁻(g): −348.6 kJ/mol, oo laga helay jiidashada elektaroonka ee 3.6131 eV ee NIST Chemistry WebBook. Ugu dambayn, Na⁺(g) + Cl⁻(g) → NaCl(s) wuxuu sii daayaa tamarta shabagga, U.

Falgalka guud waa Na(s) + ½ Cl₂(g) → NaCl(s), iyadoo ΔH°f = −411.2 kJ/mol. Sidaa darteed 107.5 + 121.3 + 495.8 − 348.6 − U = −411.2, taasoo bixisa U = 787.2 kJ/mol. U fiirso in ionaysigu ku kaco tamar ka badan inta jiidashada elektaroonku soo celiso. La'aanteed tamarta shabagga weyn, samaynta NaCl curiyayaashiisa ma noqon lahayn exothermic. Tamarta shabagga ee NaCl ee la daabacay waxay ku kala duwan yihiin dhawr boqolkiiba iyadoo ku xiran xogta iyo habka la isticmaalay (OpenStax waxay soo xigatay 769 kJ), sidaa darteed barbar dhig isbeddellada, ha barbar dhigin tirooyinka ugu dambeeya.

Ka qiyaasidda enthalpy-ga falgalka tamarta xidhiidhada

Falgallada heerka gaaska, waxaad ku qiyaasi kartaa ΔH adigoo tirinaya xidhiidhada: ΔH ≈ Σ(tamarta xidhiidhada la jebiyey) − Σ(tamarta xidhiidhada la sameeyey). Tamarta xidhiidhada ee shaxaha ku jirta waa celcelis molekiyuullo badan, sidaa darteed natiijadu waa qiyaas oo keliya waxayna ka lumi kartaa qiimaha laga helo enthalpy-yada samaysanka tobanaan kilojoule.

Tusaale la xaliyey 3. Qiyaas ΔH ee C₂H₄(g) + H₂(g) → C₂H₆(g). Afarta xidhiidh C–H ee ethylene way badbaadaan, sidaa darteed iska dhaaf. La jebiyey: hal C=C (611 kJ/mol) iyo hal H–H (436 kJ/mol), wadar ahaan 1047 kJ. La sameeyey: hal C–C (345 kJ/mol) iyo laba C–H oo cusub (2 × 415 kJ/mol), wadar ahaan 1175 kJ. ΔH ≈ 1047 − 1175 = −128 kJ. Qiimaha enthalpy-ga samaysanka, ee Lifaaqa G, waa −84.0 − 52.4 = −136.4 kJ. Qiyaastu waxay leedahay calaamadda saxda ah waxayna ku jirtaa qiyaastii 6%.

Fahamyada khaldan ee xidhiidhka ee laga fogaado

Khaladaadka badankoodu waxay ka yimaadaan u qaadashada hagitaanno qiyaas ah xeerar sax ah ama isku qasidda heshiisyada calaamadda. Kuwani waa kuwa ugu caamsan.

• U qaadashada ΔEN = 1.8 xariiq fiiqan oo u dhexeysa covalent iyo ayoon. Cabbirku waa joogto, isku-dhisyada sida HF iyo SiF₄-na way jebiyaan xeerka.
• Isku qaldidda elektaroonaysiga iyo jiidashada elektaroonka. Jiidashada elektaroonku waa tamar la cabbiray oo atam gaas ah; elektaroonaysiguna wuxuu sharxaa atam xidhiidh ku jira.
• Malaynta in atamka elektaroonaysigiisu sarreeyo had iyo jeer yahay kan aan birta ahayn ee aad filan lahayd. Hubi shaxda: xidhiidhada B–H iyo Si–H, hydrogen waa cirifka taban.
• Rogidda qaacidada tamarta xidhiidhka. Waa xidhiidhada la jebiyey laga jaray xidhiidhada la sameeyey, oo ah nidaamka ka soo horjeeda qaacidada enthalpy-ga samaysanka.
• Isku qasidda heshiisyada calaamadda tamarta shabagga hal wareeg Born–Haber gudihiisa.
• U tirinta xidhiidh laba-laab ah laba xidhiidh keli ah. Xidhiidhka C=C (611 kJ/mol) wuu ka daciifsan yahay laba xidhiidh C–C (690 kJ/mol).