VSEPR Theory: Molecules ke Shapes ko Predict karne ka Tarika ke liye use kiya jata hai, jo electron pairs se bana hota hai jo molecule ke central atoms ke aas paas hote hain. Ye theory pehli baar Sidgwick aur Powell ne 1940 mein present ki thi. VSEPR theory ka assumption ye hai ki molecule aisa shape lega jisme us atom ke valence shell mein electronic repulsion minimize ho.
By Dr.Santosh Kumar Dakhle
VSEPR Theory: Molecules ke Shapes ko Predict karne ka Tarika
Table of Content
VSEPR Theory kya hai?
Postulates
Limitations
Shapes of Molecules
What is VSEP Number?
VSEPR Theory and Shapes of Molecules
Frequently Asked Questions
VSEPR Theory kya hai?
Valence Shell Electron Pair Repulsion Theory jo ki VSEPR theory ke naam se jana jata hai, ye premise par based hai ki sabhi atoms mein valence electrons ke pairs mein repulsion hota hai, aur atoms hamesha aise arrange honge jisme ye electron pair repulsion minimize ho. Ye arrangement atom ka geometry determine karta hai jo resulting molecule banata hai.
VSEPR theory ke hisab se molecules jo alag alag geometries assume kar sakte hain, unhe neeche diye gaye illustration mein dekha ja sakta hai.
diagram
VSEPR theory ke do primary founders Ronald Nyholm aur Ronald Gillespie hain. Ye theory ko Gillespie-Nyholm theory bhi kaha jata hai in chemists ki honour mein.
VSEPR theory ke hisab se, do electrons ke beech ka repulsion Pauli exclusion principle se hota hai jo ki electrostatic repulsion se zyada important hai molecular geometry ke determination mein.
VSEPR Theory ke postulates: VSEPR theory ke postulates neeche diye gaye hain
Polyatomic molecules mein (i.e. molecules jo teen ya usse zyada atoms se bane hote hain), ek constituent atom ko central atom identify kiya jata hai jisse molecule ke sabhi dusre atoms jude hote hain.
Valence shell electron pairs ka total number molecule ka shape decide karta hai.
Electron pairs aise orient hote hain ki unke beech ka electron-electron repulsion minimize ho aur unke beech ki distance maximize ho.
Valence shell ko ek sphere ki tarah socha ja sakta hai jisme electron pairs surface par aise localize hote hain ki unke beech ki distance maximize ho.
Agar central atom ke aas paas bond pairs of electrons ho to, asymmetrically shaped molecule expect kiya ja sakta hai.
Agar central atom ke aas paas lone pairs aur bond pairs of electrons dono ho to, molecule ka shape distorted ho sakta hai.
VSEPR theory ko molecule ke har resonance structure par apply kiya ja sakta hai.
Repulsion ka strength do lone pairs mein sabse zyada hota hai aur do bond pairs mein sabse kam hota hai.
Agar central atom ke aas paas ke electron pairs ek dusre se zyada close ho to, wo ek dusre ko repel karenge. Isse molecule ki energy mein increase hota hai.
Agar electron pairs ek dusre se door ho to, unke beech ka repulsion kam hoga aur eventually, molecule ki energy low hogi.
VSEPR Theory ke limitations: VSEPR theory ke kuch significant limitations neeche diye gaye hain:
Ye theory isoelectronic species (i.e. elements jo same number of electrons rakhte hain) ko explain nahi kar pata. Ye species shapes mein vary kar sakte hain bawajood same number of electrons rakhne ke.
VSEPR theory transition metals ke compounds par koi light nahi dalta. Kuch aise compounds ke structure ko ye theory correctly describe nahi kar pata. Ye isliye hai kyunki VSEPR theory substituent groups aur lone pairs ke associated sizes ko nahi lekar chalta hai th.
What is VSEP Number?
VSEP Number yeh batata hai ki molecule ka shape kaisa hai, jaisa ki neeche diye gaye table mein bataya gaya hai.
| VSEP Number | The shape of the Molecule |
| 2 | Linear |
| 3 | Trigonal Planar |
| 4 | Tetrahedral |
| 5 | Trigonal Bipyramidal |
| 6 | Octahedral |
| 7 | Pentagonal Bipyramidal |
In sabhi shapes ko aap pehle diye gaye chitra mein bhi dekh sakte hain. Lekin, VSEPR theory se hum molecule mein atoms ke beech ke exact bond angles nahi nikal sakte hain.
Ab hum har shape ke baare mein detail se baat karenge:
Linear Shape of Molecule:
Is tarah ke molecule mein hum central atom ke valence shell mein do jagah dekhte hain. Unhe aise arrange kiya jata hai ki electrons ke beech ka repulsion kam ho sake (ulta disha mein pointing karte hue). Udaharan: BeF2
Trigonal Planar Shape of Molecule:
Is tarah ke molecule mein hum central atom se teen molecules jude hue dekhte hain. Unhe aise arrange kiya jata hai ki electrons ke beech ka repulsion kam ho sake (ek samantar trikon ke corners ki taraf pointing karte hue). Udaharan: BF3
Tetrahedral Shape of Molecule:
Do-aayami molecules mein atoms ek hi plane mein hote hain aur agar hum in conditions ko methane par lagayein, toh hume ek square samtal geometry milega jismein H-C-H ke beech ka bond angle 900 hoga.
Ab, agar hum in sabhi conditions ko teen-aayami molecule ke liye sochein, toh hume ek chaturbhujakar molecule milega jismein H-C-H ke beech ka bond angle 109028’ hoga (ek samantar trikon ke corners ki taraf pointing karte hue) CH4.
Trigonal Bipyramidal Shape of Molecule:
Ek udaharan lete hain PF5 ka. Yahaan, repulsion ko kam kiya ja sakta hai electrons ko Trigonal shikhar ke corner ki taraf barabar bant kar. Trigonal Bipyramidal mein teen positions molecule ke equator ke along hote hain. Do positions ek axis ke along hote hain jo equatorial plane se perpendicular hote hain.
VSEPR Theory ka istemaal Molecules ke Shapes ko Predict karne ke liye kaise kiya ja sakta hai?
Ek lone pair aur ek bond pair ke beech mein electrons ka repulsion do lone pairs aur do bond pairs ke beech mein repulsion ke beech mein hota hai. Electron pairs ke beech mein repulsion ka order yeh hai:
Lone Pair- lone pair > Lone Pair- bond- pair > Bond Pair- bond pair.
1.Central atom ke aas paas total number of electron pairs = ½ (central atom ke valence electrons ka number + single bonds se central atom se jude hue atoms ka number)
-Negative ions ke liye, central atom ke valence electrons mein ions par negative charge ke units ke barabar electrons ko jod dein.
– Positive ions ke liye, central atom ke valence electrons se ions par positive charge ke units ke barabar electrons ko ghatayein.
2.Bond pair ka number = Single bonds se central atom se jude hue atoms ka total number.
3.Lone pairs ka number = Total number of electron – No of shared pair
Central atom ke aas paas ke electron pairs ek dusre ko repel karte hain aur itna door chale jaate hain ek dusre se ki unke beech mein koi bhi zyada repulsion na ho. Isse molecule mein minimum energy aur maximum stability hoti hai.
-Sirf do atoms waale molecule ka shape hamesha Linear hota hai.
-Teen ya usse zyada atoms waale molecules mein, ek atom ko central atom kaha jaata hai aur baaki atoms central atom se jude hote hain.
-Agar central atom similar atoms se juda hua hai aur sirf bond pairs of electrons se ghira hua hai, toh unke beech ka repulsion similar hota hai. Isse molecule ka shape samtal hota hai aur molecule ko regular geometry waala kaha jaata hai.
-Agar central atom different atoms se juda hua hai ya phir bond pair ke saath saath lone pair of electrons se bhi ghira hua hai, toh unke beech ka repulsion similar nahi hota hai. Isse molecule ka shape irregular ya distorted hota hai.
-Molecule ka exact shape central atom ke aas paas present electron pairs ki total number par depend karta hai.
VSEPR Theory par Aksar Pooche Jaane Waale Sawaal VSEPR Theory ka premise kya hai?
Valence shell mein electron pairs ke beech mein jo repulsion hota hai, usse atoms aise arrange hote hain ki yeh repulsion kam ho sake. Yeh seedha seedha atom dwara banaye gaye molecule ke geometry ko prabhavit karta hai.
Agar VSEP number 5 ho toh molecule ka shape kaisa hoga?
Molecule ka ek Trigonal Bipyramidal structure hoga.
VSEPR theory ke kya fayde hain? Is theory ka istemaal bahut saare compounds ke molecules ke shapes ko accurately predict karne ke liye kiya ja sakta hai. Jab molecule ka geometry samajh mein aa jaata hai, toh uske reactions ko samajhna aasaan ho jaata hai.