Answer the following questions below: 1. Ammonia (NH3) is polar molecule while boron trifluoride (BF3) is a nonpolar molecule. Explain the difference in the polarity of these compounds. 2. Suppose that AB3E, a hypothetical molecule, is discovered. Predict whether the molecule is polar or nonpolar by determining its molecular shape. Note: A corresponds to central atom, B-terminal atom Elone pair (nonbonding electrons)
The Correct Answer and Explanation is :
1. Polarity of Ammonia (NH₃) and Boron Trifluoride (BF₃)
The difference in the polarity of ammonia (NH₃) and boron trifluoride (BF₃) arises from their molecular geometry and the distribution of electron density.
- Ammonia (NH₃): NH₃ is a polar molecule because it has a trigonal pyramidal shape due to the presence of a lone pair of electrons on the nitrogen atom. The nitrogen atom is more electronegative than hydrogen, creating a dipole moment where the electrons are pulled toward the nitrogen. Additionally, the asymmetry of the lone pair causes the dipole moments of the N-H bonds to not cancel each other out, resulting in a net dipole moment.
- Boron Trifluoride (BF₃): BF₃, on the other hand, is a nonpolar molecule. It has a planar trigonal structure with 120° bond angles, and the dipole moments of the B-F bonds cancel out because of their symmetrical arrangement around the central boron atom. Despite boron being less electronegative than fluorine, the symmetry eliminates any net dipole moment.
2. Predicting the Polarity of AB₃E
The molecular shape of AB₃E is trigonal pyramidal. This geometry results from three bonded atoms and one lone pair on the central atom (A). The lone pair creates an asymmetric electron distribution, leading to a non-uniform spatial arrangement.
- Polarity Prediction: Since AB₃E has a trigonal pyramidal shape, it is likely to be polar. The lone pair on the central atom contributes to an uneven distribution of electron density, causing dipole moments in the bonds to not cancel each other out. The central atom’s lone pair typically distorts the molecule, reinforcing the asymmetry and ensuring a net dipole moment.
In summary, NH₃ is polar due to its asymmetrical trigonal pyramidal shape, while BF₃ is nonpolar due to its symmetrical planar structure. Similarly, the AB₃E molecule is predicted to be polar because of its trigonal pyramidal geometry and the influence of the lone pair of electrons on the central atom.