Even though the following molecules contain polar bonds, the only polar molecule is:
A. CCl4
B. CO2
C. NH3
D. CH4
The Correct Answer and Explanation is:
The correct answer is C. NH3 (ammonia).
To understand why NH3 is the only polar molecule among the given options, it is important to consider both the polarity of individual bonds and the overall molecular geometry.
- Polar Bonds: A polar bond occurs when there is a significant difference in electronegativity between the atoms involved, causing a distribution of charge. For instance, in NH3, the nitrogen atom is more electronegative than the hydrogen atoms, resulting in polar N-H bonds.
- Molecular Geometry: The shape of a molecule significantly affects its polarity. NH3 has a trigonal pyramidal shape due to the presence of a lone pair of electrons on the nitrogen atom. This geometry prevents the bond dipoles from cancelling each other out, leading to a net dipole moment that makes the entire molecule polar.
- Other Options:
- A. CCl4 (carbon tetrachloride): Although C-Cl bonds are polar, CCl4 has a tetrahedral geometry. The symmetry of the molecule allows the dipole moments of the polar bonds to cancel each other out, resulting in a nonpolar molecule.
- B. CO2 (carbon dioxide): CO2 has polar C=O bonds, but its linear geometry allows the bond dipoles to cancel out, making the molecule nonpolar.
- D. CH4 (methane): In CH4, the C-H bonds are slightly polar; however, the symmetrical tetrahedral shape results in the cancellation of bond dipoles, rendering the molecule nonpolar as well.
In summary, while CCl4, CO2, and CH4 contain polar bonds, their symmetrical geometries lead to an overall nonpolar character. In contrast, NH3, with its trigonal pyramidal structure and unbalanced dipole moments, is a polar molecule. This polarity affects its properties, such as higher boiling points and solubility in water, which are characteristic of polar substances.