Explain the difference in polarity between NH4+ and NH3 based on differences in their electron geometries, molecular geometries and symmetries.
The Correct Answer and Explanation is:
The difference in polarity between NH4+ (ammonium ion) and NH3 (ammonia) can be explained by looking at their electron geometries, molecular geometries, and symmetries.
- Electron Geometry:
- NH4+: The ammonium ion has four bonding pairs of electrons and no lone pairs on the nitrogen atom. The electron geometry is tetrahedral because it has four bonding regions arranged around the central nitrogen.
- NH3: Ammonia has three bonding pairs of electrons and one lone pair on the nitrogen atom. The electron geometry is tetrahedral as well, but due to the lone pair, it is adjusted to a trigonal pyramidal molecular geometry.
- Molecular Geometry:
- NH4+: With no lone pairs on the nitrogen, the molecular geometry of NH4+ is tetrahedral. The symmetrical arrangement of the four bonds around the nitrogen atom results in a nonpolar molecule, as the dipoles cancel each other out.
- NH3: In ammonia, the lone pair on nitrogen distorts the geometry, making it trigonal pyramidal. This geometry leads to an uneven distribution of charge, with a partial negative charge on the nitrogen and partial positive charges on the hydrogen atoms, making NH3 polar.
- Symmetry:
- NH4+: Because the four hydrogen atoms are symmetrically arranged around the nitrogen atom in a tetrahedral shape, the dipoles from each N-H bond cancel each other out. As a result, NH4+ has high symmetry and is nonpolar.
- NH3: The trigonal pyramidal shape of ammonia is asymmetrical due to the lone pair of electrons on nitrogen. This lack of symmetry prevents the cancellation of dipole moments, making NH3 polar with a net dipole moment pointing towards the nitrogen atom.
In summary, NH4+ is nonpolar due to its symmetric tetrahedral geometry, while NH3 is polar due to its asymmetric trigonal pyramidal shape and the presence of a lone pair.
