Among H2S, H2O, NF3, NH3 and CHCl3, identify the molecule (X) with lowest dipole moment value. The number of lone pairs of electrons present on the central atom of the molecule (X) is :
- 3
- 2
- 0
- 1
Answer
(4) 1
Solution
Dipole moments (in D): H2O (1.85) > NH3 (1.47) > CHCl3 (1.04) > H2S (0.95) > NF3 (0.23)
As per NCERT, in NH3 the orbital dipole of the lone pair on N is in the same direction as the resultant of the N–H bond dipoles, whereas in NF3 it is opposite to the resultant of the N–F bond dipoles (F is more electronegative than N), so the moments largely cancel.
X = NF3 (lowest dipole moment).
In NF3, N has 5 valence electrons; 3 are used in the three N–F bonds 1 lone pair on N (pyramidal shape).
Answer: (4)