3.4.1
Intuition Badi picture (YE theory KYU exist karti hai)1890s mein chemists ke paas ek puzzle tha: C o C l 3 N H 3 C o C l 3 ⋅ 6 N H 3 Do saturated molecules aapas mein kaise chipak sakti hain? Alfred Werner ki genius (1893, Nobel 1913) ye thi ki unhone kaha: ek metal mein do alag tarah ki valency hoti hai, aur doosri wali space mein fixed directions mein point karti hai. Ye ek hi idea formulas, conductivity, colours, aur isomers — sab kuch explain karta hai — bina kabhi ek atom "dekhe".
Definition Werner ke postulates
Har metal do types ki valency exhibit karta hai:
Primary valency (ab = oxidation state ): negative ions se satisfy hoti hai, ionizable hai, aur non-directional hai.Secondary valency (ab = coordination number, CN ): ligands (neutral molecules ya negative ions) se satisfy hoti hai, non-ionizable hai, aur directional / space mein fixed hai.
Har metal ki ek fixed secondary valency (CN) hoti hai, jaise Co(III) → 6, Pt(IV) → 6, Pt(II)/Cu(II) → 4.
Secondary valencies space mein fixed positions ki taraf directed hoti hain → isse geometry fix hoti hai (CN 6 ke liye octahedral, CN 4 ke liye square planar/tetrahedral).
Intuition DO TARAH KI VALENCY KYU?Metal ko aisa socho jisme ek inner ring hai jisme fixed "hand-holds" (secondary, CN) hain jo ligands ko tight pakdte hain, aur ek outer cloud of charge (primary, oxidation state) hai jo counter-ions se balance hoti hai jo paani mein door chale jaate hain. Inner ring kabhi nahi chodti jab dissolve hota hai; outer ions chhod dete hain (ionize ho jaate hain). Ye separation hi poori theory hai.
Square brackets ke andar [ ] coordination sphere → atoms jo secondary valency se pakde hain (the complex ion). Ye ionize NAHI hote.Brackets ke bahar = counter ions jo primary valency se pakde hain → ye paani mein ionize HOTE HAIN .
coordination sphere [ C o metal ( N H 3 ) 6 ] ionizable C l 3
Werner ne measure kiya ki kitne C l − A g N O 3 free / ionized C l −
Old formula
Werner formula
CN (fixed)
Ions in solution
C l − A g N O 3
C o C l 3 ⋅ 6 N H 3 [ C o ( N H 3 ) 6 ] C l 3 6
4
3
C o C l 3 ⋅ 5 N H 3 [ C o ( N H 3 ) 5 C l ] C l 2 6
3
2
C o C l 3 ⋅ 4 N H 3 [ C o ( N H 3 ) 4 C l 2 ] C l 6
2
1
C o C l 3 ⋅ 3 N H 3 [ C o ( N H 3 ) 3 C l 3 ] 6
0
0
[ C o ( N H 3 ) 5 C l ] C l 2 Given: C o C l 3 ⋅ 5 N H 3 2 C l − A g N O 3
CN abhi bhi 6 KYU hai? Co(III) ki fixed secondary valency 6 hai. Hamare paas 5 N H 3 ek aur ligand chahiye → ek C l − andar jaana chahiye.Ek Cl andar KYU? Kyunki sirf 2 (3 nahi) Cl⁻ ionize hote hain → teesra Cl⁻ secondary valency se locked hai, isliye wo ek ligand hai, counter ion nahi.Andar charge: C o 3 + + 5 ( N H 3 , 0 ) + 1 ( C l − , − 1 ) = + 3 − 1 = + 2 Counter ions: + 2 2 C l − Formula: [ C o ( N H 3 ) 5 C l ] C l 2 3 ions mein tootta hai: [ C o ( N H 3 ) 5 C l ] 2 + + 2 C l −
Worked example Forecast-then-Verify:P tC l 4 ⋅ 2 K C l Pehle forecast karo (answer cover karo): Pt(IV) CN = 6. Hamare paas 4 Cl hain aur KCl se provided hain. Formula aur ion count predict karne ki koshish karo.
Pt(IV) ko 6 ligands chahiye; 4 C l − C l − [ P tC l 6 ] 2 −
Charge: + 4 + 6 ( − 1 ) = − 2 2 K +
Verify: K 2 [ P tC l 6 ] 2 K + + [ P tC l 6 ] 2 − A g N O 3 0 Cl precipitate hota hai (sab ligands hain). ✓
Intuition Werner ne geometryKAISE PROVE ki bina microscopes ke
Agar secondary valencies fixed directions mein point karti hain, toh [ M a 4 b 2 ] b ek doosre ke paas (cis) baith sakte hain ya opposite (trans) . Werner ne actually isolate kiye gaye isomers ki sankhya count ki:
Octahedral → [ M a 4 b 2 ] 2 isomers (cis + trans). ✓ (experiment se match kiya)Hexagonal-planar ya trigonal-prism 3 predict karte. ✗
Prakriti jitne isomers deti hai woh shape batata hai. Brilliant: bottles count karna = 3D geometry deduce karna.
[ C o ( N H 3 ) 5 C l ] C l 2 A g N O 3 Ye sahi kyun lagta hai: 3 chlorines hain aur A g N O 3 + C l − → A g C l Galti: sirf ionized (outside-bracket) C l − andar wala Cl secondary valency se locked hai aur available nahi hai. Fix: sirf wo Cl count karo jo bracket ke bahar likha ho → yahan, 2 .
Common mistake "Primary valency = metal ke bonds ki sankhya."Ye sahi kyun lagta hai: valency ka matlab usually bonds hota hai. Galti: yahan primary valency = oxidation state (non-directional charge balance), jabki actual metal–ligand bonds count karne wala secondary valency = coordination number hai. Fix: bonds → CN; balance karne ke liye charge → primary valency.
Common mistake "CN ligandmolecules ki sankhya ke barabar hai."
Ye sahi kyun lagta hai: ek molecule, ek bond — usually. Galti: polydentate ligands (jaise en, oxalate) metal ko do ya zyada points pe pakdte hain; en ka ek molecule CN mein 2 contribute karta hai. Fix: CN = donor atoms / coordinate bonds ki sankhya, molecules ki sankhya nahi.
Intuition Honest limits (taaki tum ise over-trust na karo)Werner ne shape, formulas, conductivity, isomers explain kiye — apne time ke liye superb. Usne explain NAHI kiya ki ek metal ki particular CN KYU hoti hai, na colour ya magnetism . Unke liye baad ki electronic theories (VBT, Crystal Field Theory) chahiye thi. Werner ne skeleton diya; CFT ne electrons diye.
Recall Feynman: ek 12-saal ke bachche ko explain karoSocho ek metal atom ek aisa insaan hai jiske paas do haath hain aur ek coin ki jeb hai.
Haath (secondary valency) ek fixed number of toys (ligands) pakdte hain aur unhe fixed positions mein rakhte hain — ye KABHI nahi chhodte, chahe swimming pool (paani) mein bhi ho.Coins (primary valency, +charge) bahar khade doston (counter ions) ko pay kiye jaate hain. Swimming pool mein, wo dost tair ke door chale jaate hain (ionize ho jaate hain).
Toh jab tum "tester" (A g N O 3
Mnemonic Do valencies yaad rakhne ka tarika"PIN vs SiD" —
P rimary = I onizable, N on-directional (oxidation state).
S econdary = non-ionizable; aasaan: S econdary = S patial (directional) = C N = brackets ke andar ligands.
Quick line: "Bracket ke andar tight pakad (secondary); bahar waala tair ke jaata hai (primary)."
Werner's primary valency corresponds to which modern concept? Metal ka Oxidation state (ionizable, non-directional).
Werner's secondary valency corresponds to which modern concept? Coordination number (non-ionizable, directional/fixed in space).
Ek coordination compound ke kaunse ions paani mein ionize hote hain? Counter ions jo square brackets ke BAHAR likhe hain (primary valency se pakde).
[ C o ( N H 3 ) 3 C l 3 ] A g N O 3 Teeno Cl⁻ bracket ke andar ligands hain (secondary valency); zero free/ionizable Cl⁻ hain, aur complex neutral hai.
[ C o ( N H 3 ) 4 C l 2 ] C l A g N O 3 Sirf 1 (bracket ke bahar wala akela Cl).
Co(III) aur Pt(IV) ki fixed secondary valency (CN) kya hai? 6 (octahedral).
C o C l 3 ⋅ 5 N H 3 [ C o ( N H 3 ) 5 C l ] C l 2
Complex ion ka charge kaise aata hai? Metal ka oxidation state + ligand charges ka sum.
Werner ne CN 6 ke liye octahedral geometry kaise deduce ki? [ M a 4 b 2 ]
Ek cheez jo Werner's theory explain NAHI kar saki? Colour aur magnetism ki origin / ek specific CN KYU hoti hai (VBT/CFT chahiye).
'en' jaisa ek bidentate ligand CN mein kitna contribute karta hai? 2, kyunki ye 2 donor atoms se bind karta hai.
Puzzle: saturated molecules combine
Primary valency = oxidation state
Secondary valency = coordination number
Geometry: octahedral or square planar
Q = OS metal + sum ligand charges
AgNO3 precipitates free Cl-
