Question

question 4 (2 points)
pyramidal molecules like nh₃ with 1 reds are 2 symmetrical/asymmetrical and 3 nonpolar/polar
pyramidal molecules like ncl₃ with 4 reds are 5 symmetrical/asymmetrical and 6 nonpolar/polar note that ncl₃ has only nonpolar bonds
a. symmetrical b. asymmetrical c. nonpolar d. polar
e. 0 f. 1 g. 2 h. 3 i. 4

Explanation:

• For \(NH_3\):
• The number of regions of electron density (REDS) around the central \(N\) atom is calculated by considering bonding and non - bonding electron pairs. In \(NH_3\), there are 3 \(N - H\) bonds and 1 lone pair. So the total number of REDS is \(3 + 1=4\).
• Pyramidal molecules like \(NH_3\) are asymmetrical. The presence of a lone pair distorts the shape from a perfectly symmetrical tetrahedral (if all 4 REDS were bonding) to a pyramidal shape.
• Since the molecule is asymmetrical and there is a difference in electronegativity between \(N\) and \(H\) (\(N\) is more electronegative), the dipoles do not cancel out, making \(NH_3\) polar.
• For \(NCl_3\):
• The central \(N\) atom in \(NCl_3\) has 3 \(N - Cl\) bonds and 1 lone pair. So the number of REDS is \(3+1 = 4\).
• Similar to \(NH_3\), the presence of a lone pair makes the pyramidal \(NCl_3\) molecule asymmetrical.
• Although the \(N - Cl\) bonds are non - polar (as per the note), the asymmetrical shape (due to the lone pair) means that the overall molecule is polar. The lone pair affects the electron distribution in the molecule.

Answer:

1. I
2. B
3. D
4. I
5. B
6. D