Chemical Bonding — Chemistry STD 11 Science — Question
Maharashtra BoardEnglish MediumSTD 11 ScienceChemistryChemical Bonding4 Marks
Question
$BF _3$ molecule is planar but $NH _3$ pyramidal. Explain.
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Answer
i. In the $BF _3$ molecule, the central boron atom undergoes $sp ^2$ hybridization giving rise to three $sp ^2$ hybridized orbitals directed towards three comers of an equilateral triangle. Thus, the geometry is trigonal planar.ii. In the $NH _3$ molecule, the central nitrogen atom undergoes $sp ^3$ hybridization giving rise to four $sp ^3$ hybridized orbitals directed towards four comers of a tetrahedron. The expected geometry of $NH _3$ molecule is regular tetrahedral with bond angle $109^{\circ} 28^{\prime}$. There is one lone pair of electrons in one of the $sp ^3$ hybrid orbitals of nitrogen. The lone pair-bond pair repulsion distorts the bond angle. Hence, the structure of $NH _3$ is distorted and it has pyramidal geometry.
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