JEE Main 2004 — Chemical Bonding And Molecular Structure Question with Solution
From: AIEEE 2004
Question
The correct order of bond angles (smallest first) in H2S, NH3, BF3 and SiH4 is
Choose an option
Show full solutionCorrect option: C
Correct answer
CH2S < NH3 < SiH4 < BF3
Step-by-step explanation
1. In H2S molecule, central atom S is a 3rd period element and according to Dragos rule, when a 3rd period or higher period element overlap with a small element whose electronegetivity is low then that over lapping cannot be a effective overlapping, because of higher size of 3rd or higher periods element and smaller size of low electronegative element.
Here in H2S, H atom has very low electronegativity and smaller in size so it create more negative charge around sulphur(S) atom and size of S2 ion increases, because of this higher size difference efficiency overlapping is not possible. So, any hybridization do not happen in between S and H atom. Lone pair electrons of S atom is present in the pure orbital like s, px, py, pz and it look like this :
As we know the angle between and py is 90o, so bond angle is 90o.
2. In NH3, 3 Bond pair(BP) + 1 lone pair (LP) present so angle between bond 107o.
3. BF3 has sp2 hybridization. So bond angle is 120o.
4.
Here Si is sp3 hybridised and shape is regular tetrahedral and bond angle 109o 28'
Here in H2S, H atom has very low electronegativity and smaller in size so it create more negative charge around sulphur(S) atom and size of S2 ion increases, because of this higher size difference efficiency overlapping is not possible. So, any hybridization do not happen in between S and H atom. Lone pair electrons of S atom is present in the pure orbital like s, px, py, pz and it look like this :
As we know the angle between and py is 90o, so bond angle is 90o.
2. In NH3, 3 Bond pair(BP) + 1 lone pair (LP) present so angle between bond 107o.
3. BF3 has sp2 hybridization. So bond angle is 120o.
4.
Here Si is sp3 hybridised and shape is regular tetrahedral and bond angle 109o 28'
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This is a previous-year question from JEE Main 2004, covering the Chemical Bonding And Molecular Structure chapter of Chemistry. PrepSharp catalogues every PYQ from JEE Main with a verified answer key and step-by-step solution prepared by IIT alumni — so you can search by chapter, topic or year and revise efficiently.