Question

Which pair has permanent dipole moment for both the members?

• A. $N{O}_2$ and $C{O}_2$
• B. $N{O}_2$ and $O_3$
• C. $Si{F}_4$ and $C{O}_2$
• D. $Si{F}_4$ and $N{O}_2$

Answer 1

The correct option is B

$N{O}_2$ and $O_3$

$C{O}_2$ is a linear symmetrical molecule which looks like

$O\stackrel{\text{⇷}}{=}C\stackrel{\text{⇸}}{=}O$

Each one of the dipole moments cancel each other resulting in zero net dipole moment.

For $Si{F}_4$ from VSEPR, ep = $\frac{4+4}{2}=4$ i.e. tetrahedral geometry with 4 ligands and no lone pair.

$\therefore$ $Si{F}_4$ is a symmetric molecule and will not have any dipole moment.

Thus, the answer is B.

$N{O}_2$ looks like:


As you can see, there will clearly be a dipole moment because it looks like water and is also made up of different elements.

$O_3$ looks like:



Ozone has a bent shape like water and thus, the individual dipole moments cannot cancel each other. The individual dipole moment is caused by resonance in the Ozone molecule which you have studied.