Which one of the following molecules has maximum dipole moment ?

CONCEPT:

Dipole Moment

• Dipole moment is a measure of the separation of positive and negative charges in a molecule. It depends on both the magnitude of the charge difference and the distance between the charges.
• For molecules with a symmetric geometry, the individual bond dipoles may cancel out, resulting in a net dipole moment of zero.
• For molecules with an asymmetric distribution of charges, the dipoles do not cancel out, resulting in a net dipole moment.

Explanation:-

CH4 & PF5 , µnet = 0 (non polar)

1. NF₃ (Nitrogen trifluoride)
   • NF₃ has a trigonal pyramidal shape similar to NH₃.
   • However, the electronegativity of fluorine is higher than nitrogen, leading to a net dipole moment that is directed towards fluorine.
2. CH₄ (Methane)
   • CH₄ has a tetrahedral shape with all four hydrogen atoms symmetrically distributed around the carbon atom.
   • The C-H bonds have very similar electronegativity, so they cancel out each other’s dipoles, resulting in a net dipole moment of zero.
3. NH₃ (Ammonia)
   • NH₃ has a trigonal pyramidal shape with a lone pair of electrons at the nitrogen atom.
   • This asymmetry, combined with the N-H bond dipoles, results in a significant net dipole moment directed towards the lone pair on the nitrogen atom.
4. PF₅ (Phosphorus pentafluoride)
   • PF₅ has a trigonal bipyramidal structure with all bond dipoles symmetrically arranged around the phosphorus atom.
   • This arrangement causes the dipoles to cancel each other out, resulting in a net dipole moment of zero.

• Comparing the molecules:
  • NF₃ has a dipole moment, but fluorine's high electronegativity reduces it compared to NH₃.
  • CH₄ and PF₅ have net dipole moments of zero due to their symmetrical shapes.
  • NH₃ has a significant dipole moment due to the lone pair on nitrogen and the asymmetric arrangement of hydrogen atoms.

The molecule with the maximum dipole moment is NH₃