3.4.6
Intuition Ek hi saans mein badi baatEk complex mein metal atom aisa behave karta hai jaise wo chahta ho ki uske aas-paas itne electrons ho jaayein ki wo nearest noble gas ki copy ban jaaye . Ligands electron pairs donate karte hain, aur jab metal ke around total electron count agle noble gas ke electron count ke barabar ho jaata hai, tab complex khaas taur pe stable hota hai. Yahi total count hota hai Effective Atomic Number (EAN) .
Definition Effective Atomic NumberKisi complex mein central metal ka EAN wo total electrons hote hain jo us metal ke paas dikhte hain — inhe count karte hain:
wo electrons jo metal ion par bache hote hain (apna charge banane ke liye electrons kho dene ke baad), aur
wo electrons jo saare ligands ne donate kiye hain (har donor atom / coordinate bond se 2 electrons).
EAN = Z − ( oxidation state ) + 2 × ( coordination number )
jahan Z neutral metal ka atomic number hai.
Worked example Step-by-step:[ Co(NH 3 ) 6 ] 3 + Step 1 — Metal ka Z Cobalt, Z = 27 Yeh step kyun? EAN neutral atom ke total electrons se start hota hai.
Step 2 — Oxidation state nikalo. NH 3 + 3 ⇒ + 3 Kyun? Ion banane mein jo electrons khoy, wo ab count nahi hote.
Step 3 — Metal ion par bache electrons = 27 − 3 = 24
Step 4 — Donated electrons = 2 × CN = 2 × 6 = 12 Kyun? 6 NH3 −
Step 5 — EAN = 24 + 12 = 36 = Kr . ✔ Rule maanta hai → stable hai.
[ Fe(CN) 6 ] 4 −
Fe: Z = 26 − − 1 − 6 − 4 = − 4 − ( − 6 ) = + 2 Kyun? Charges ka sum overall charge ke barabar hona chahiye: x + 6 ( − 1 ) = − 4
Metal par electrons = 26 − 2 = 24
Donated = 2 × 6 = 12
EAN = 24 + 12 = 36 =
[ Ni(CO) 4 ]
Ni: Z = 28 ⇒ 0
Metal par electrons = 28 − 0 = 28
Donated = 2 × 4 = 8
EAN = 36 = 4
Worked example Ek complex jo NAHI maanta:[ Ni(NH 3 ) 6 ] 2 +
Ni Z = 28 + 2 = 6
EAN = ( 28 − 2 ) + 12 = 38 Nahi 36. ✘
Seekh: Bahut saare real, bilkul stable complexes EAN nahi maante. Yeh rule ek guide hai, sabse zyada metal carbonyls aur low-oxidation-state species ke liye kaam karta hai — koi law nahi hai .
Recall Compute karne se pehle predict karo: kya[ Cr(CO) 6 ] Forecast: Cr ka Z = 24 Verify: EAN = 24 + 12 = 36 = d
Common mistake "Har ligand 1 electron donate karta hai."Yeh sahi kyun lagta hai: Hum "har ligand ka ek bond" kehte hain, aur ek bond matlab ek electron lagta hai.
Sahi baat: Ek coordinate (dative) bond ek lone pair = 2 electrons se banta hai, dono ligand ki taraf se. Isliye CN ko 2 se multiply karo, 1 se nahi.
Common mistake "Complex ka charge hi metal ka oxidation state hai."Yeh sahi kyun lagta hai: Bracket par dikhne wala number tempting hota hai.
Sahi baat: Oxidation state = complex charge minus ligand charges ka sum. Jaise [ Fe(CN) 6 ] 4 − − 4 + 2
Common mistake "Agar EAN ≠ noble gas, toh complex exist hi nahi kar sakta."Yeh sahi kyun lagta hai: Ek "rule" sunne mein law lagta hai.
Sahi baat: EAN ek stability heuristic hai. [ Ni(NH 3 ) 6 ] 2 + [ PtCl 4 ] 2 −
Common mistake "EAN aur 18-electron rule alag cheezein hain."Yeh sahi kyun lagta hai: Alag naam, alag chapters hain.
Sahi baat: Dono ek hi idea ko do tarike se count karte hain . EAN metal ke saare electrons count karta hai (noble-gas Z valence electrons count karta hai (18 aim karta hai = filled n s n p ( n − 1 ) d −
Intuition Ek hi sikke ke do pehluNoble gas Kr ka Z = 36 18 valence electrons hain (4 s 2 3 d 10 4 p 6 = 36 ⇔ 18 valence electrons ." Yahi wajah hai ki Ni(CO) 4 Cr(CO) 6 Fe(CO) 5 −
EAN ka full form kya hai? Effective Atomic Number — ek complex mein central metal ke around total (apparent) electrons.
EAN ka formula likho. EAN = Z − (oxidation state) + 2 × (coordination number).
Coordination number ko 2 se kyun multiply karte hain? Har ligand ek lone pair = 2 electrons coordinate bond ke zariye donate karta hai.
EAN rule batao. Ek complex tab khaas taur pe stable hota hai jab uska EAN nearest noble gas ke atomic number ke barabar ho (2,10,18,36,54,86).
EAN of [Ni(CO)₄]? 28 − 0 + 2×4 = 36 (Kr). Rule maanta hai.
EAN of [Fe(CN)₆]⁴⁻? Fe ka oxidation state +2 hai: (26−2) + 2×6 = 36 (Kr).
EAN of [Co(NH₃)₆]³⁺? (27−3) + 12 = 36 (Kr).
Kya [Ni(NH₃)₆]²⁺ EAN maanta hai? Nahi, EAN = (28−2)+12 = 38 ≠ 36. EAN ek guide hai, law nahi.
EAN aur 18-electron rule mein kya relation hai? EAN minus noble-gas-core electrons = valence count; EAN = noble gas Z ⇔ 18 valence electrons.
Complex mein metal ka oxidation state kaise nikalte hain? Overall complex charge minus ligand charges ka sum.
EAN rule kisne propose kiya? Nevil Sidgwick ne.
Recall Feynman: 12-saal ke bacche ko samjhaoSocho metal ek aisa bacha hai jise tab sabse zyada khushi milti hai jab uski plate poori cookies se bhari ho — bilkul utni jitni "cool kid" (noble gas) ke paas hain jo uske paas baitha hai. Metal pehle kuch cookies de deta hai kyunki wo charged hai (yahi oxidation state hai), phir har dost (ligand) use 2 cookies (ek lone pair) deta hai. Agar saari gifting ke baad metal ki plate mein bilkul utni hi cookies hain jitni cool kid ke paas hain, toh wo super khush aur stable hai. Woh khushi wala number hi EAN hai. Kabhi kabhi ek bacha thoda alag number se bhi khush rehta hai — isliye yeh ek achha guess hai, strict law nahi.
Mnemonic Formula yaad karo"Z minus charge, plus two per friend."
(Z 2 × He-Ne-Ar-Kr-Xe-Rn = 2,10,18,36,54,86 → "2 10 18, 36 54 86 ."
Coordination number — "×2" term provide karta hai.Oxidation state of central metal — "− charge" term hai.18-electron rule — EAN ka valence-only version hai.Metal carbonyls — woh complexes jin ke liye EAN sabse achha predict karta hai.Coordinate (dative) bond — isliye har ligand 2 electrons deta hai.Noble gas configuration — stability ka target hai.Werner's theory — broader bonding context hai.
donate lone pairs 2 per bond
Neutral metal Z electrons
